2019 Book AquaponicsFoodProductionSystem
2019 Book AquaponicsFoodProductionSystem
2019 Book AquaponicsFoodProductionSystem
Alyssa Joyce
Benz Kotzen
Gavin M. Burnell Editors
Aquaponics
Food Production
Systems
Combined Aquaculture and Hydroponic
Production Technologies for the Future
Aquaponics Food Production Systems
Simon Goddek • Alyssa Joyce • Benz Kotzen •
Gavin M. Burnell
Editors
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Preface
It has been more than 45 years since the science fiction film Soylent Green (1973)
first appeared in cinemas. The movie was prescient for its time and predicted many
of our current environmental problems, including dying oceans, the greenhouse
effect, overpopulation, and loss of biodiversity. Even though we hope that humans
will not serve as a future nutrient source, the scenarios laid out in the movie are not
that far from being realised. As researchers and citizens, we realise our duty of care
to the environment and the rest of our world’s ever-growing population. We are
concerned that if we stand back and ignore the current trends in exploitation of
resources and methods of production that our paradise of a planet will be doomed or
at least far diminished, such that living on the sterile surfaces of the Moon or Mars
will seem like a pleasant alternative. Generations to come will and should hold us
individually and collectively responsible for the mess that we leave. The numerous
authors of this book are in a lucky as well as in an unfortunate position, in that we can
either help to solve problems or be held responsible by future generations for being
part of the problem. When we started the COST Action FA1305 ‘The EU
Aquaponics Hub – Realising Sustainable Integrated Fish and Vegetable Production
for the EU’, aquaponics was a niche technology that, at an industrial scale, could not
compete with stand-alone hydroponics and aquaculture technologies. However,
aquaponics technology in the past decade has taken great leaps forward in efficiency
and hence economic viability through a wide range of technological advances. As
our ability to understand the environmental costs of industrial farming increases, we
are more capable of developing technologies to ensure that farming is more produc-
tive and less damaging to the environment. This positive outcome should be
bolstered by the very encouraging signs that although young people are statistically
not interested in being the farmers of the future, they do want to be future farmers if
technology is involved and they can adapt these technologies to live closer to urban
environments and have a better quality of life than in the rural past. Kids of all ages
are fascinated by technology, and it is no wonder as technology solves many
problems. At the same time though, kids (perhaps less so with teenagers) are also
environmentally conscious and understand that the future of our planet lies in the
v
vi Preface
The editors, authors, and publishers would like to acknowledge the COST (European
Cooperation in Science and Technology) organisation (https://www.cost.eu) initially
for funding and supporting the 4-year COST Action 1305, ‘The EU Aquaponics Hub
– Realising Sustainable Integrated Fish and Vegetable Production for the EU’, which
was conceived and chaired by Benz Kotzen, University of Greenwich, and then finally
for contributing funds to this publication, making it open-source and available to all to
read. Without COST, who brought almost all of the authors together, in an amazing
project, this book would not have been written, and without their final dissemination
contribution, this book would not be available to everyone. We also acknowledge and
greatly appreciate the support of Desertfoods International GmbH (www.desertfoods-
international.com) and Developonics asbl (www.developonics.com) for the additional
financial support required to enable the publication to be open-source. Additionally we
applaud the efforts and great skill of Aquaponik Manufaktur GmbH (www.aquaponik-
manufaktur.de) for producing a cohesive and attractive set of illustrations for the book,
the Netherlands Organisation for Scientific Research (NWO; project number 438-17-
402) for supporting Simon Goddek in his editorial work and writing, and the Swedish
Research Council FORMAS grant 2017-00242 for similarly supporting Alyssa Joyce
whilst she undertook editorial work and writing on this book. Finally, the editors are
indebted to the enthusiasm and diligence of its authors, especially of the 22 lead
authors of the 24 chapters in their sterling efforts to get this remarkable book delivered
on time. A heartfelt well-done one and all!
ix
Contents
xi
xii Contents
xv
xvi About the Editors
Abstract As the world’s population grows, the demands for increased food pro-
duction expand, and as the stresses on resources such as land, water and nutrients
become ever greater, there is an urgent need to find alternative, sustainable and
reliable methods to provide this food. The current strategies for supplying more
produce are neither ecologically sound nor address the issues of the circular econ-
omy of reducing waste whilst meeting the WHO’s Millennium Development Goals
of eradicating hunger and poverty by 2015. Aquaponics, a technology that integrates
aquaculture and hydroponics, provides part of the solution. Although aquaponics has
developed considerably over recent decades, there are a number of key issues that
still need to be fully addressed, including the development of energy-efficient
systems with optimized nutrient recycling and suitable pathogen controls. There is
also a key issue of achieving profitability, which includes effective value chains and
efficient supply chain management. Legislation, licensing and policy are also keys to
the success of future aquaponics, as are the issues of education and research, which
are discussed across this book.
S. Goddek (*)
Mathematical and Statistical Methods (Biometris), Wageningen University, Wageningen,
The Netherlands
e-mail: simon.goddek@wur.nl; simon@goddek.nl
A. Joyce
Department of Marine Science, University of Gothenburg, Gothenburg, Sweden
e-mail: alyssa.joyce@gu.se
B. Kotzen
School of Design, University of Greenwich, London, UK
e-mail: b.kotzen@greenwich.ac.uk
M. Dos-Santos
ESCS-IPL, DINÂMIA’CET, ISCTE-Institute University of Lisbon, Lisbon, Portugal
e-mail: mjpls@iscte-iul.pt
1.1 Introduction
Biosphere Integrity
Genetic Diversity Functional Diversity
Land-System Atmospheric
Change Aerosol Loading
Phosphorus Nitrogen
Fig. 1.1 Current status of the control variables for seven of the planetary boundaries as described
by Steffen et al. (2015). The green zone is the safe operating space, the yellow represents the zone of
uncertainty (increasing risk), the red is a high-risk zone, and the grey zone boundaries are those that
have not yet been quantified. The variables outlined in blue (i.e. land-system change, freshwater use
and biochemical flows) indicate the planetary boundaries that aquaponics can have a positive
impact on
1 Aquaponics and Global Food Challenges 5
The 2030 Agenda for Sustainable Development emphasizes the need to tackle global
challenges, ranging from climate change to poverty, with sustainable food produc-
tion a high priority (Brandi 2017; UN 2017). As reflected in the UN’s Sustainable
Development Goal 2 (UN 2017), one of the greatest challenges facing the world is
how to ensure that a growing global population, projected to rise to around 10 billion
by 2050, will be able to meet its nutritional needs. To feed an additional two billion
people by 2050, food production will need to increase by 50% globally (FAO 2017).
Whilst more food will need to be produced, there is a shrinking rural labour force
because of increasing urbanization (dos Santos 2016). The global rural population
has diminished from 66.4% to 46.1% in the period from 1960 to 2015 (FAO 2017).
Whilst, in 2017, urban populations represented more than 54% of the total world
population, nearly all future growth of the world’s population will occur in urban
6 S. Goddek et al.
areas, such that by 2050, 66% of the global population will live in cities (UN 2014).
This increasing urbanization of cities is accompanied by a simultaneously growing
network of infrastructure systems, including transportation networks.
To ensure global food security, total food production will need to increase by
more than 70% in the coming decades to meet the Millennium Development Goals
(FAO 2009), which include the ‘eradication of extreme poverty and hunger’ and also
‘ensuring environmental sustainability’. At the same time, food production will
inevitably face other challenges, such as climate change, pollution, loss of biodiver-
sity, loss of pollinators and degradation of arable lands. These conditions require the
adoption of rapid technological advances, more efficient and sustainable production
methods and also more efficient and sustainable food supply chains, given that
approximately a billion people are already chronically malnourished, whilst agricul-
tural systems continue to degrade land, water and biodiversity at a global scale
(Foley et al. 2011; Godfray et al. 2010).
Recent studies show that current trends in agricultural yield improvements will
not be sufficient to meet projected global food demand by 2050, and these further
suggest that an expansion of agricultural areas will be necessary (Bajželj et al. 2014).
However, the widespread degradation of land in conjunction with other environ-
mental problems appears to make this impossible. Agricultural land currently covers
more than one-third of the world’s land area, yet less than a third of it is arable
(approximately 10%) (World Bank 2018). Over the last three decades, the availabil-
ity of agricultural land has been slowly decreasing, as evidenced by more than 50%
decrease from 1970 to 2013. The effects of the loss of arable land cannot be
remedied by converting natural areas into farmland as this very often results in
erosion as well as habitat loss. Ploughing results in the loss of topsoil through wind
and water erosion, resulting in reduced soil fertility, increased fertilizer use and then
eventually to land degradation. Soil losses from land can then end up in ponds, dams,
lakes and rivers, causing damage to these habitats.
In short, the global population is rapidly growing, urbanizing and becoming
wealthier. Consequently, dietary patterns are also changing, thus creating greater
demands for greenhouse gas (GHG) intensive foods, such as meat and dairy prod-
ucts, with correspondingly greater land and resource requirements (Garnett 2011).
But whilst global consumption is growing, the world’s available resources, i.e. land,
water and minerals, remain finite (Garnett 2011). When looking at the full life-cycle
analysis of different food products, however, both Weber and Matthews (2008) and
Engelhaupt (2008) suggest that dietary shifts can be a more effective means of
lowering an average household’s food-related climate footprint than ‘buying
local’. Therefore, instead of looking at the reduction of supply chains, it has been
argued that a dietary shift away from meat and dairy products towards nutrition-
oriented agriculture can be more effective in reducing energy and footprints
(Engelhaupt 2008; Garnett 2011).
The complexity of demand-supply imbalances is compounded by deteriorating
environmental conditions, which makes food production increasingly difficult
and/or unpredictable in many regions of the world. Agricultural practices cannot
only undermine planetary boundaries (Fig. 1.1) but also aggravate the persistence
1 Aquaponics and Global Food Challenges 7
and propagation of zoonotic diseases and other health risks (Garnett 2011). All these
factors result in the global food system losing its resilience and becoming increas-
ingly unstable (Suweis et al. 2015).
The ambitious 2015 deadline of the WHO’s Millennium Development Goals
(MDGs) to eradicate hunger and poverty, to improve health and to ensure environ-
mental sustainability has now passed, and it has become clear that providing
nutritious food for the undernourished as well as for affluent populations is not a
simple task. In summary, changes in climate, loss of land and diminution in land
quality, increasingly complex food chains, urban growth, pollution and other
adverse environmental conditions dictate that there is an urgent need to not only
find new ways of growing nutritious food economically but also locate food pro-
duction facilities closer to consumers. Delivering on the MDGs will require changes
in practice, such as reducing waste, carbon and ecological footprints, and aquaponics
is one of the solutions that has the potential to deliver on these goals.
Whilst aquaponics is seen to be one of the key food production technologies which
‘could change our lives’ (van Woensel et al. 2015), in terms of sustainable and
efficient food production, aquaponics can be streamlined and become even more
efficient. One of the key problems in conventional aquaponics systems is that the
nutrients in the effluent produced by fish are different than the optimal nutrient
solution for plants. Decoupled aquaponics systems (DAPS), which use water from
the fish but do not return the water to the fish after the plants, can improve on
traditional designs by introducing mineralization components and sludge bioreactors
containing microbes that convert organic matter into bioavailable forms of key
minerals, especially phosphorus, magnesium, iron, manganese and sulphur that are
deficient in typical fish effluent. Contrary to mineralization components in one-loop
systems, the bioreactor effluent in DAPS is only fed to the plant component instead
of being diluted in the whole system. Thus, decoupled systems that utilize sludge
digesters make it possible to optimize the recycling of organic wastes from fish as
nutrients for plant growth (Goddek 2017; Goddek et al. 2018). The wastes in such
systems mainly comprise fish sludge (i.e. faeces and uneaten feed that is not in
solution) and thus cannot be delivered directly in a hydroponics system. Bioreactors
(see Chap. 10) are therefore an important component that can turn otherwise
unusable sludge into hydroponic fertilizers or reuse organic wastes such as stems
and roots from the plant production component into biogas for heat and electricity
generation or DAPS designs that also provide independently controlled water
cycling for each unit, thus allowing separation of the systems (RAS, hydroponic
and digesters) as required for the control of nutrient flows. Water moves between
components in an energy and nutrient conserving loop, so that nutrient loads and
flows in each subsystem can be monitored and regulated to better match downstream
requirements. For instance, phosphorous (P) is an essential but exhaustible fossil
8 S. Goddek et al.
resource that is mined for fertilizer, but world supplies are currently being depleted at
an alarming rate. Using digesters in decoupled aquaponics systems allows microbes
to convert the phosphorus in fish waste into orthophosphates that can be utilized by
plants, with high recovery rates (Goddek et al. 2016, 2018).
Although decoupled systems are very effective at reclaiming nutrients, with near-
zero nutrient loss, the scale of production in each of the units is important given that
nutrient flows from one part of the system need to be matched with the downstream
production potential of other components. Modelling software and Supervisory
Control and Data Acquisition (SCADAS) data acquisition systems therefore become
important to analyse and report the flow, dimensions, mass balances and tolerances
of each unit, making it possible to predict physical and economic parameters
(e.g. nutrient loads, optimal fish-plant pairings, flow rates and costs to maintain
specific environmental parameters). In Chap. 11, we will look in more detail at
systems theory as applied to aquaponics systems and demonstrate how modelling
can resolve some of the issues of scale, whilst innovative technological solutions can
increase efficiency and hence profitability of such systems. Scaling is important not
only to predict the economic viability but also to predict production outputs based on
available nutrient ratios.
Another important issue, which requires further development, is the use and reuse
of energy. Aquaponics systems are energy and infrastructure intensive. Depending
on received solar radiation, the use of solar PV, solar thermal heat sources and (solar)
desalination may still not be economically feasible but could all be potentially
integrated into aquaponics systems. In Chap. 12, we present information about
innovative technical and operational possibilities that have the capacity to overcome
the inherent limitations of such systems, including exciting new opportunities for
implementing aquaponics systems in arid areas.
In Chap. 2, we also discuss in more detail the range of environmental challenges
that aquaponics can help address. Pathogen control, for instance, is very important,
and contained RAS systems have a number of environmental advantages for fish
production, and one of the advantages of decoupled aquaponics systems is the ability
to circulate water between the components and to utilize independent controls
wherein it is easier to detect, isolate and decontaminate individual units when
there are pathogen threats. Probiotics that are beneficial in fish culture also appear
beneficial for plant production and can increase production efficiency when circu-
lated within a closed system (Sirakov et al. 2016). Such challenges are further
explored in Chap. 5, where we discuss in more detail how innovation in aquaponics
can result in (a) increased space utilization efficiency (less cost and materials,
maximizing land use); (b) reduced input resources, e.g. fishmeal, and reduced
negative outputs, e.g. waste discharge; and (c) reduced use of antibiotics and
pesticides in self-contained systems.
There are still several aquaponic topic areas that require more research in order to
exploit the full potential of these systems. From a scientific perspective, topics such
as nitrogen cycling (Chap. 9), aerobic and anaerobic remineralization (Chap. 10),
water and nutrient efficiency (Chap. 8), optimized aquaponic fish diets (Chap. 13)
and plant pathogens and control strategies (Chap. 14) are all high priorities.
1 Aquaponics and Global Food Challenges 9
Waste
Independent, RAS systems and hydroponics units also have a wide range of
operational challenges that are discussed in detail in Chaps. 3 and 4. Increasingly,
technological advances have allowed for higher productivity ratios (Fig. 1.2), which
can be defined as a fraction of the system’s outputs (i.e. fish and plants) over the
system’s input (i.e. fish feed and/or additional fertilization, energy input for lighting,
heating and pumping CO2 dosing and biocontrols).
When considering the many challenges that aquaponics encounters, production
problems can be broadly broken down into three specific themes: (1) system pro-
ductivity, (2) effective value chains and (3) efficient supply chain management.
System Productivity Agricultural productivity is measured as the ratio of agricul-
tural outputs to agricultural inputs. Traditional small-scale aquaponics systems were
designed primarily to address environmental considerations such as water discharge,
water inputs and nutrient recycling, but the focus in recent years has increasingly
shifted towards economic feasibility in order to increase productivity for large-scale
farming applications. However, this will require the productivity of aquaponics
systems to be able to compete economically with independent, state-of-the-art
hydroponics and aquaculture systems. If the concept of aquaponics is to be success-
fully applied at a large scale, the reuse of nutrients and energy must be optimized, but
end markets must also be considered.
Effective Value Chains The value chains (added value) of agricultural products
mainly arise from the processing of the produce such as the harvested vegetables,
fruits and fish. For example, the selling price for pesto (i.e. red and green) can be
more than ten times higher than that of the tomatoes, basil, olive oil and pine nuts. In
addition, most processed food products have a longer shelf life, thus reducing
spoilage. Evidently, fresh produce is important because nutritional values are mostly
higher than those in the processed foods. However, producing fresh and high-quality
produce is a real challenge and therefore a luxury in many regions of the world.
Losses of nutrients during storage of fruit and vegetables are substantial if they are
not canned or frozen quickly (Barrett 2007; Rickman et al. 2007). Therefore, for
large-scale systems, food processing should at least be considered to balance out any
fluctuations between supply and demand and reduce food waste. With respect to
food waste reduction, vegetables that do not meet fresh produce standards, but are
still of marketable quality, should be processed in order to reduce postharvest losses.
1 Aquaponics and Global Food Challenges 11
Although such criteria apply to all agricultural and fisheries products, value adding
can substantially increase the profitability of the aquaponics farm, especially if
products can reach niche markets.
Efficient Supply Chain Management In countries with well-developed transpor-
tation and refrigeration networks, fruit and vegetables can be imported from all
around the world to meet consumer demands for fresh produce. But as mentioned
previously, high-quality and fresh produce is a scarce commodity in many parts of
the world, and the long-distance movement of goods – i.e. supply chain management
– to meet high-end consumer demand is often criticized and justifiably so. Most
urban dwellers around the world rely on the transport of foods over long distances to
meet daily needs (Grewal and Grewal 2012). One of the major criticisms is thus the
reliance on fossil fuels required to transport products over large distances (Barrett
2007). The issue of food miles directs focus on the distance that food is transported
from the time of production to purchase by the end consumer (Mundler and Criner
2016). However, in terms of CO2 emissions per tonne/km (tkm), one food mile for
rail transportation (13.9 g CO2/tkm) is not equal to one food mile of truck/road
transportation, as truck transportation has more than 15 times greater environmental
impact (McKinnon 2007). Therefore, transportation distance is not necessarily the
only consideration, as the ecological footprint of vegetables grown on farms in rural
areas is potentially less than the inputs required to grow food in greenhouses closer
to urban centres.
Food miles are thus only a part of the picture. Food is transported long distances,
but the greenhouse gas emissions associated with food production are dominated by
the production phase (i.e. the impact of energy for heating, cooling and lighting)
(Engelhaupt 2008; Weber and Matthews 2008). For example, Carlsson (1997)
showed that tomatoes imported from Spain to Sweden in winter have a much
lower carbon footprint than those locally grown in Sweden, since energy inputs to
greenhouses in Sweden far outweigh the carbon footprint of transportation from
Spain. When sourcing food, the transport of goods is not the only factor to take into
consideration, as the freshness of products determines their nutritive value, taste and
general appeal to consumers. By growing fresh food locally, many scholars agree
that urban farming could help secure the supply of high-quality produce for urban
populations of the future whilst also reducing food miles (Bon et al. 2010; dos Santos
2016; Hui 2011). Both areas will be discussed in more detail in Sect. 1.5.
From a consumer’s perspective, urban aquaponics thus has advantages because of
its environmental benefits due to short supply chains and since it meets consumer
preferences for high-quality locally produced fresh food (Miličić et al. 2017).
However, despite these advantages, there are a number of socio-economic concerns:
The major issue involves urban property prices, as land is expensive and often
considered too valuable for food production. Thus, purchasing urban land most
likely makes it impossible to achieve a feasible expected return of investment.
However, in shrinking cities, where populations are decreasing, unused space
could be used for agricultural purpose (Bontje and Latten 2005; Schilling and
Logan 2008) as is the case in Detroit in the United States (Mogk et al. 2010).
12 S. Goddek et al.
Additionally, there is a major issue of urban planning controls, where in many cities
urban land is not designated for agricultural food production and aquaponics is seen
to be a part of agriculture. Thus, in some cities aquaponic farming is not allowed.
The time is ripe to engage with urban planners who need to be convinced of the
benefits of urban farms, which are highly productive and produce fresh, healthy,
local food in the midst of urban and suburban development.
9000 900
8000 800
Numbers of Publications
Numbers of Publications
6000 600
(RAS)
5000 500
4000 400
3000 300
2000 200
1000 100
Fig. 1.3 The number of papers published on ‘hydroponics’, ‘RAS’ and ‘aquaponics’ from 1980 to
2018 (data were collected from the Scopus database on 30 January 2019). Please note that the scale
for ‘RAS’ is one order of magnitude higher than that for ‘hydroponics’ and ‘aquaponics’
papers are considerably lower (Fig. 1.3), but the numbers are rising and will continue
to rise as aquaponics education, especially at university level, and general interest
increases. A ‘hype ratio’ can be described as an indicator of the popularity of a
subject in the public media relative to what is published in the academic press. This
can, for example, be calculated by taking the search results in Google divided by the
search results in Google Scholar. In the case of aquaponics, the hype ratio on
16 August 2016 was 1349, which is considerable when compared to the hype ratios
of hydroponics (131) and recirculating aquaculture (17) (Junge et al. 2017). The
sense one gets from this is that, indeed, aquaponics is an emerging technology but
that there is enormous interest in the field which is likely to continue and increase
over the next decades. The hype ratio, however, is likely to decline as more research
is undertaken and scientific papers are published.
This book is aimed at the aquaponics researcher and practitioner, and it has been
designed to discuss, explore and reveal the issues that aquaponics is addressing now
and that will no doubt arise in the future. With such a broad spectrum of topics, it
aims to provide a comprehensive but easily accessible overview of the rather novel
scientific and commercial field of aquaponics. Apart from the production and
technical side, this book has been designed to address trends in food supply and
demand, as well as the various economic, environmental and social implications of
this emerging technology. The book has been co-authored by numerous experts from
around the world, but mostly from within the EU. Its 24 chapters cover the whole
gamut of aquaponics areas and will provide a necessary textbook for all those
interested in aquaponics and moving aquaponics forwards into the next decade.
1 Aquaponics and Global Food Challenges 15
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Open Access This chapter is licensed under the terms of the Creative Commons Attribution 4.0
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Chapter 2
Aquaponics: Closing the Cycle on Limited
Water, Land and Nutrient Resources
A. Joyce (*)
Department of Marine Science, University of Gothenburg, Gothenburg, Sweden
e-mail: alyssa.joyce@gu.se
S. Goddek
Mathematical and Statistical Methods (Biometris), Wageningen University, Wageningen,
The Netherlands
e-mail: simon.goddek@wur.nl; simon@goddek.nl
B. Kotzen
School of Design, University of Greenwich, London, UK
e-mail: b.kotzen@greenwich.ac.uk
S. Wuertz
Department Ecophysiology and Aquaculture, Leibniz-Institute of Freshwater Biology and
Inland Fisheries, Berlin, Germany
e-mail: wuertz@igb-berlin.de
2.1 Introduction
The term ‘tipping point’ is currently being used to describe natural systems that are
on the brink of significant and potentially catastrophic change (Barnosky et al.
2012). Agricultural food production systems are considered one of the key ecolog-
ical services that are approaching a tipping point, as climate change increasingly
generates new pest and disease risks, extreme weather phenomena and higher global
temperatures. Poor land management and soil conservation practices, depletion of
soil nutrients and risk of pandemics also threaten world food supplies.
Available arable land for agricultural expansion is limited, and increased agricul-
tural productivity in the past few decades has primarily resulted from increased
cropping intensity and better crop yields as opposed to expansion of the agricultural
landmass (e.g. 90% of gains in crop production have been a result of increased
productivity, but only 10% due to land expansion) (Alexandratos and Bruinsma
2012; Schmidhuber 2010). Global population is estimated to reach 8.3–10.9 billion
people by 2050 (Bringezu et al. 2014), and this growing world population, with a
corresponding increase in total as well as per capita consumption, poses a wide range
of new societal challenges. The United Nations Convention to Combat Desertifica-
tion (UNCCD) Global Land Outlook Working Paper 2017 report notes worrying
trends affecting food production (Thomas et al. 2017) including land degradation,
loss of biodiversity and ecosystems, and decreased resilience in response to envi-
ronmental stresses, as well as a widening gulf between food production and demand.
The uneven distribution of food supplies results in inadequate quantities of food, or
lack of food of sufficient nutritional quality for part of the global population, while in
other parts of the world overconsumption and diseases related to obesity have
become increasingly common. This unbalanced juxtaposition of hunger and malnu-
trition in some parts of the world, with food waste and overconsumption in others,
reflects complex interrelated factors that include political will, resource scarcity, land
affordability, costs of energy and fertilizer, transportation infrastructure and a host of
other socioeconomic factors affecting food production and distribution.
Recent re-examinations of approaches to food security have determined that a
‘water-energy-food nexus’ approach is required to effectively understand, analyse
and manage interactions among global resource systems (Scott et al. 2015). The
nexus approach acknowledges the interrelatedness of the resource base – land, water,
energy, capital and labour – with its drivers, and encourages inter-sectoral consul-
tations and collaborations in order to balance different resource user goals and
interests. It aims to maximize overall benefits while maintaining ecosystem integrity
in order to achieve food security. Sustainable food production thus requires reduced
utilization of resources, in particular, water, land and fossil fuels that are limited,
costly and often poorly distributed in relation to population growth, as well as
recycling of existing resources such as water and nutrients within production
systems to minimize waste.
2 Aquaponics: Closing the Cycle on Limited Water, Land and Nutrient Resources 21
Over the last 50 years, total food supply has increased almost threefold, whereas the
world’s population has only increased twofold, a shift that has been accompanied by
significant changes in diet related to economic prosperity (Keating et al. 2014). Over
the last 25 years, the world’s population increased by 90% and is expected to reach
the 7.6 billion mark in the first half of 2018 (Worldometers). Estimates of increased
world food demand in 2050 relative to 2010 vary between 45% and 71% depending
on assumptions around biofuels and waste, but clearly there is a production gap that
needs to be filled. In order to avoid a reversal in recent downward trends under-
nourishment, there must be reductions in food demand and/or fewer losses in food
production capacity (Keating et al. 2014). An increasingly important reason for
rising food demand is per capita consumption, as a result of rising per capita income,
which is marked by shifts towards high protein foods, particularly meat (Ehrlich and
Harte 2015b). This trend creates further pressures on the food supply chain, since
animal-based production systems generally require disproportionately more
resources, both in water consumption and feed inputs (Rask and Rask 2011; Ridoutt
et al. 2012; Xue and Landis 2010). Even though the rate of increasing food demand
has declined in recent decades, if current trajectories in population growth and
dietary shifts are realistic, global demand for agricultural products will grow at
1.1–1.5% per year until 2050 (Alexandratos and Bruinsma 2012).
Population growth in urban areas has put pressure on land that has been tradi-
tionally used for soil-based crops: demands for housing and amenities continue to
encroach on prime agricultural land and raise its value well beyond what farmers
could make from cultivation. Close to 54% of the world’s population now lives in
urban areas (Esch et al. 2017), and the trend towards urbanization shows no signs of
abating. Production systems that can reliably supply fresh foods close to urban
centres are in demand and will increase as urbanization increases. For instance, the
rise of vertical farming in urban centres such as Singapore, where land is at a
premium, provides a strong hint that concentrated, highly productive farming sys-
tems will be an integral part of urban development in the future. Technological
advances are increasingly making indoor farming systems economical, for instance
the development of LED horticultural lights that are extremely long lasting and
22 A. Joyce et al.
2.3.1 Predictions
Even as more food needs to be produced, usable land for agricultural practices is
inherently limited to roughly 20–30% of the world’s land surface. The availability of
agricultural land is decreasing, and there is a shortage of suitable land where it is
most needed, i.e. particularly near population centres. Soil degradation is a major
contributor to this decline and can generally be categorized in two ways: displace-
ment (wind and water erosion) and internal soil chemical and physical deterioration
(loss of nutrients and/or organic matter, salinization, acidification, pollution, com-
paction and waterlogging). Estimating total natural and human-induced soil degra-
dation worldwide is fraught with difficulty given the variability in definitions,
severity, timing, soil categorization, etc. However, it is generally agreed that its
consequences have resulted in the loss of net primary production over large areas
(Esch et al. 2017), thus restricting increases in arable and permanently cropped land
to 13% in the four decades from the early 1960s to late 1990s (Bruinsma 2003).
More importantly in relation to population growth during that time period, arable
land per capita declined by about 40% (Conforti 2011). The term ‘arable land’
implies availability of adequate nutrients to support crop production. To counteract
nutrient depletion, worldwide fertilizer consumption has risen from 90 kg/ha in 2002
to 135 kg in 2013 (Pocketbook 2015). Yet the increased use of fertilizers often
results in excesses of nitrate and phosphates ending up in aquatic ecosystems
(Bennett et al. 2001), causing algal blooms and eutrophication when decaying
algal biomass consumes oxygen and limits the biodiversity of aquatic life. Large-
scale nitrate and phosphate-induced environmental changes are particularly evident
in watersheds and coastal zones.
Nitrogen, potassium and phosphorus are the three major nutrients essential for
plant growth. Even though demand for phosphorus fertilizers continues to grow
2 Aquaponics: Closing the Cycle on Limited Water, Land and Nutrient Resources 23
exponentially, rock phosphate reserves are limited and estimates suggest they will be
depleted within 50–100 years (Cordell et al. 2011; Steen 1998; Van Vuuren et al.
2010). Additionally, anthropogenic nitrogen input is expected to drive terrestrial
ecosystems towards greater phosphorous limitations, although a better understand-
ing of the processes is critical (Deng et al. 2017; Goll et al. 2012; Zhu et al. 2016).
Currently, there are no substitutes for phosphorus in agriculture, thus putting con-
straints on future agricultural productivity that relies on key fertilizer input of mined
phosphate (Sverdrup and Ragnarsdottir 2011). The ‘P-paradox’, in other words, an
excess of P impairing water quality, alongside its shortage as a depleting
non-renewable resource, means that there must be substantial increases in recycling
and efficiency of its use (Leinweber et al. 2018).
Modern intensive agricultural practices, such as the frequency and timing of
tillage or no-till, application of herbicides and pesticides, and infrequent addition
of organic matter containing micronutrients can alter soil structure and its microbial
biodiversity such that the addition of fertilizers no longer increases productivity per
hectare. Given that changes in land usage have resulted in losses of soil organic
carbon estimated to be around 8%, and projected losses between 2010 and 2050 are
3.5 times that figure, it is assumed that soil water-holding capacity and nutrient
losses will continue, especially in view of global warming (Esch et al. 2017).
Obviously there are trade-offs between satisfying human needs and not compromis-
ing the ability of the biosphere to support life (Foley et al. 2005). However, it is
clear when modelling planetary boundaries in relation to current land use prac-
tices that it is necessary to improve N and P cycling, principally by reducing both
nitrogen and phosphorus emissions and runoff from agricultural land, but also by
better capture and reuse (Conijn et al. 2018).
One of the principal benefits of aquaponics is that it allows for the recycling of
nutrient resources. Nutrient input into the fish component derives from feed, the
composition of which depends on the target species, but feed in aquaculture typically
constitutes a significant portion of input costs and can be more than half the total
annual cost of production. In certain aquaponics designs, bacterial biomass can also
be harnessed as feed, for instance, where biofloc production makes aquaponic
systems increasingly self-contained (Pinho et al. 2017).
Wastewater from open-cage pens or raceways is often discharged into
waterbodies, where it results in nutrient pollution and subsequent eutrophication.
By contrast, aquaponic systems take the dissolved nutrients from uneaten fish feed
and faeces, and utilizing microbes that can break down organic matter, convert the
nitrogen and phosphorous into bioavailable forms for use by plants in the hydro-
ponics unit. In order to achieve economically acceptable plant production levels, the
24 A. Joyce et al.
presence of appropriate microbial assemblages reduces the need to add much of the
supplemental nutrients that are routinely used in stand-alone hydroponic units. Thus
aquaponics is a near-zero discharge system that offers not only economic benefit
from both fish and plant production streams, but also significant reductions in both
environmentally noxious discharges from aquaculture sites. It also eliminates the
problem of N- and P-rich runoff from fertilizers used in soil-based agriculture. In
decoupled aquaponic systems, aerobic or anaerobic bioreactors can also used to treat
sludge and recover significant macro- and micronutrients in bioavailable forms for
subsequent use in hydroponic production (Goddek et al. 2018) (see Chap. 8).
Exciting new developments such as these, many of which are now being realized for
commercial prodution, continue to refine the circular economy concept by increas-
ingly allowing for nutrient recovery.
2.4.1 Predictions
As a closed system with biosecurity measures, aquaponic systems require far fewer
chemical pesticide applications in the plant component. If seed and transplant stocks
are carefully handled and monitored, weed, fungal and bacterial/algal contaminants
can be controlled in hydroponic units with targeted measures rather than the wide-
spread preventive application of herbicides and fungicides prevalent in soil-based
agriculture. As technology continues to advance, developments such as positive
pressure greenhouses can further reduce pest problems (Mears and Both 2001).
Design features to reduce pest risks can cut costs in terms of chemicals, labour,
2 Aquaponics: Closing the Cycle on Limited Water, Land and Nutrient Resources 25
application time and equipment, especially since the land footprint of industrial-scale
aquaponics systems is small, and systems are compact and tightly contained, as
compared to the equivalent open production area of vegetable and fruit crops of
conventional soil-based farms.
The use of RAS in aquaponic systems also prevents disease transmissions
between farmed stocks and wild populations, which is a pressing concern in flow-
through and open-net pen aquaculture (Read et al. 2001; Samuel-Fitwi et al. 2012).
Routine antibiotic use is generally not required in the RAS component, since it is a
closed system with few available vectors for disease introduction. Furthermore, the
use of antimicrobials and antiparasitics is generally discouraged, as it can be
detrimental to the microbiota that are crucial for converting organic and inorganic
wastes into usable compounds for plant growth in the hydroponic unit (Junge et al.
2017). If disease does emerge, containment of both fish and plants from the
surrounding environment makes decontamination and eradication more manageable.
Although closed systems clearly do not completely alleviate all disease and pest
problems (Goddek et al. 2015), proper biocontrol measures that are already practised
in stand-alone RAS and hydroponics result in significant reductions of risk. These
issues are discussed in further detail in subsequent chapters (for fish, see Chap. 6; for
plants, further details in Chap. 14).
2.5.1 Predictions
Fig. 2.1 Water footprint Water Foodprint (litres of water per 1 kg)
(L per kg). Fish in RAS
systems use the least water
of any food production
system
modelling forecasting declining water availability in the near future for nearly all
countries (Distefano and Kelly 2017). The UN predicts that the pursuit of business-
as-usual practices will result in a global water deficit of 40% by 2030 (Water 2015).
In this respect, as groundwater supplies for irrigation are depleted or contaminated,
and arid regions experience more drought and water shortages due to climate change,
water for agricultural production will become increasingly valuable (Ehrlich and
Harte 2015a). Increasing scarcity of water resources compromises not only water
security for human consumption but also global food production (McNeill et al.
2017). Given that water scarcity is expected even in areas that currently have
relatively sufficient water resources, it is important to develop agricultural tech-
niques with low water input requirements, and to improve ecological management of
wastewater through better reuse (FAO 2015a).
The UN World Water Development Report for 2017 (Connor et al. 2017) focuses
on wastewater as an untapped source of energy, nutrients and other useful
by-products, with implications not only for human and environmental health but
also for food and energy security as well as climate change mitigation. This report
calls for appropriate and affordable technologies, along with legal and regulatory
frameworks, financing mechanisms and increased social acceptability of wastewater
treatment, with the goal of achieving water reuse within a circular economy. The
report also points to a 2016 World Economic Forum report that lists the water crisis
as the global risk of highest concern in the next 10 years.
2 Aquaponics: Closing the Cycle on Limited Water, Land and Nutrient Resources 27
Efficiencies of Production
of Conventional Meat, Fish and Crickets
Percentage of
animal edible
80 55 55 55 40
10
kg
15
20
25
Fig. 2.2 Feed conversion ratios (FCRs) based as kg of feed per live weight and kg of feed for edible
portion. Only insects, which are eaten whole in some parts of the world, have a better FCR than fish
2.6.1 Predictions
Globally, land-based crops and pasture occupy approximately 33% of total available
land, and expansion for agricultural uses between 2000 and 2050 is estimated to
increase by 7–31% (350–1500 Mha, depending on source and underlying assump-
tions), most often at the expense of forests and wetlands (Bringezu et al. 2014).
While there is currently still land classed as ‘good’ or ‘marginal’ that is available for
rain-fed agriculture, significant portions of it are far from markets, lack infrastructure
or have endemic diseases, unsuitable terrain or other conditions that limit develop-
ment potential. In other cases, remaining lands are already protected, forested or
developed for other uses (Alexandratos and Bruinsma 2012). By contrast, dryland
ecosystems, defined in the UN’s Commission on Sustainable Development as arid,
semiarid and dry subhumid areas that typically have low productivity, are threatened
by desertification and are therefore unsuitable for agricultural expansion but never-
theless have many millions of people living in close proximity (Economic 2007).
These facts point to the need for more sustainable intensification of food production
2 Aquaponics: Closing the Cycle on Limited Water, Land and Nutrient Resources 29
closer to markets, preferably on largely unproductive lands that may never become
suitable for soil-based farming.
The two most important factors contributing to agricultural input efficiencies are
considered by some experts to be (i) the location of food production in areas where
climatic (and soil) conditions naturally increase efficiencies and (ii) reductions in
environmental impacts of agricultural production (Michael and David 2017). There
must be increases in the supply of cultivated biomass achieved through the intensi-
fication of production per hectare, accompanied by a diminished environmental
burden (e.g. degradation of soil structure, nutrient losses, toxic pollution). In other
words, the footprint of efficient food production must shrink while minimizing
negative environmental impacts.
Aquaponic production systems are soilless and attempt to recycle essential nutrients
for cultivation of both fish and plants, thereby using nutrients in organic matter from
fish feed and wastes to minimize or eliminate the need for plant fertilizers. For
instance, in such systems, using land to mine, process, stockpile and transport
phosphate or potash-rich fertilizers becomes unnecessary, thus aso eliminating the
inherent cost, and cost of application, for these fertilizers.
Aquaponics production contributes not only to water usage efficiency (Sect.
2.5.2) but also to agricultural input efficiency by reducing the land footprint needed
for production. Facilities for instance, can be situated on nonarable land and in
suburban or urban areas closer to markets, thus reducing the carbon footprint
associated with rural farms and transportation of products to city markets. With a
smaller footprint, production capacity can be located in otherwise unproductive
areas such as on rooftops or old factory sites, which can also reduce land acquisition
costs if those areas are deemed unsuitable for housing or retail businesses. A smaller
footprint for production of high-quality protein and vegetables in aquaponics can
also take pressure away from clearing ecologically valuable natural and semi-natural
areas for conventional agriculture.
2.7.1 Predictions
also estimated that 30% of global energy consumption is devoted to food production
and its supply chain (FAO 2011). Greenhouse gas (GHG) emissions associated with
fossil fuels (approximately 14% in lifecycle analysis) added to those from fertilizer
manufacturing (16%) and nitrous oxide from average soils (44%) (Camargo et al.
2013), all contribute substantially to the environmental impacts of farming. A trend
in the twenty-first century to produce crop-based biofuels (e.g. corn for ethanol) to
replace fossil fuels has increased pressure on the clearing of rainforests, peatlands,
savannas and grasslands for agricultural production. However, studies point to
creation of a ‘carbon debt’ from such practices, since the overall release of CO2
exceeds the reductions in GHGs they provide by displacing fossil fuels (Fargione
et al. 2008). Arguably a similar carbon debt exists when clearing land to raise food
crops via conventional agriculture that relies on fossil fuels.
In a comparative analysis of agricultural production systems, trawling fisheries
and recirculating aquaculture systems (RAS) were found to emit GHGs 2–2.5 times
that of non-trawling fisheries and non-RAS (pen, raceway) aquaculture. In RAS,
these energy requirements relate primarily to the functioning of pumps and filters
(Michael and David 2017). Similarly, greenhouse production systems can emit up to
three times more GHGs than open-field crop production if energy is required to
maintain heat and light within optimal ranges (ibid.). However, these GHG figures
do not take into account other environmental impacts of non-RAS systems, such as
eutrophication or potential pathogen transfers to wild stocks. Nor do they consider
GHG from the production, transportation and application of herbicides and pesti-
cides used in open-field cultivation, nor methane and nitrous oxide from associated
livestock production, both of which have a 100-year greenhouse warming potential
(GWP) 25 and 298 times that of CO2, respectively (Camargo et al. 2013; Eggleston
et al. 2006).
These sobering estimates of present and future energy consumption and GHG
emissions associated with food production have prompted new modelling and
approaches, for example, the UN’s water-food-energy nexus approach mentioned
in Sect. 2.1. The UN’s Sustainable Development Goals have pinpointed the vulner-
ability of food production to fluctuations in energy prices as a key driver of food
insecurity. This has prompted efforts to make agrifood systems ‘energy smart’ with
an emphasis on improving energy efficiencies, increasing use of renewable energy
sources and encouraging integration of food and energy production (FAO 2011).
2.8 Summary
As the human population continues to increase, there is increasing demand for high-
quality protein worldwide. Compared to meat sources, fish are widely recognized as
being a particularly healthy source of protein. In relation to the world food supply,
aquaculture now provides more fish protein than capture fisheries (FAO 2016).
Globally, human per capita fish consumption continues to rise at an annual average
rate of 3.2% (1961–2013), which is double the rate of population growth. In the
period from 1974 to 2013, biologically unsustainable ‘overfishing’ has increased by
22%. During the same period, the catch from what are deemed to be ‘fully exploited’
fisheries has decreased by 26%. Aquaculture therefore provides the only possible
solution for meeting increased market demand. It is now the fastest growing food
sector and therefore an important component of food security (ibid.)
With the global population estimated to reach 8.3–10.9 billion people by 2050
(Bringezu et al. 2014), sustainable development of the aquaculture and agricultural
sectors requires optimization in terms of production efficiency, but also reductions in
utilization of limited resources, in particular, water, land and fertilizers. The benefits
of aquaponics relate not just to the efficient uses of land, water and nutrient resources
but also allow for increased integration of smart energy opportunities such as biogas
and solar power. In this regard, aquaponics is a promising technology for producing
both high-quality fish protein and vegetables in ways that can use substantially less
land, less energy and less water while also minimizing chemical and fertilizer inputs
that are used in conventional food production.
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Chapter 3
Recirculating Aquaculture Technologies
3.1 Introduction
C. A. Espinal (*)
Landing Aquaculture, Oirschot, The Netherlands
e-mail: carlos@landingaquaculture.com
D. Matulić
Department of Fisheries, Beekeeping, Game management and Special Zoology,
Faculty of Agriculture, University of Zagreb, Zagreb, Croatia
e-mail: dmatulic@agr.hr
RAS may also use UV irradiation for water disinfection (Sharrer et al. 2005;
Summerfelt et al. 2009), ozonation and protein skimming for fine solids and
microbial control (Attramadal et al. 2012a; Gonçalves and Gagnon 2011;
Summerfelt and Hochheimer 1997) and denitrification systems to remove nitrate
(van Rijn et al. 2006).
Modern recirculating aquaculture technology has been developing for more than
40 years, but novel technologies increasingly offer ways to change the paradigms of
traditional RAS including improvements on classic processes such as solids capture,
biofiltration and gas exchange. RAS has also experienced important developments in
terms of scale, production capacities and market acceptance, with systems becoming
progressively larger and more robust.
This chapter discusses how RAS technology has developed over the past two
decades from a period of technological consolidation to a new era of industrial
implementation.
The earliest scientific research on RAS conducted in Japan in the 1950s focused on
biofilter design for carp production driven by the need to use locally limited water
resources more productively (Murray et al. 2014). In Europe and the United States,
scientists similarly attempted to adapt technologies developed for domestic waste-
water treatment in order to better reuse water within recirculating systems
(e.g. activated sludge processes for sewage treatment, trickling, submerged and
down-flow biofilters and several mechanical filtration systems). These early efforts
included primarily work on marine systems for fish and crustacean production, but
were soon adopted in arid regions where the agriculture sector is restricted by water
supply. In aquaculture, different solutions have been designed to maximize water use
including highly intensive recirculating systems that incorporate water filtration
systems such as drum filters, biological filters, protein skimmers and oxygen injec-
tion systems (Hulata and Simon 2011). Despite a strong conviction by pioneers in
the industry about the commercial viability of their work, most of the early studies
focused exclusively on the oxidation of toxic inorganic nitrogen wastes derived from
protein metabolism. The trust in technology was reinforced by the successful
operation of public as well as domestic aquaria, which generally feature over-sized
treatment units to ensure crystal-clear water. Additionally, extremely low stocking
densities and associated feed inputs meant that such over-engineering still made a
relatively small contribution to capital and operational costs of the system compared
to intensive RAS. Consequently, the changes in process dynamics associated with
scale-change were unaccounted for, resulting in the under-sizing of RAS treatment
units in order to minimize capital costs. As a consequence, safety margins were far
too narrow or non-existent (Murray et al. 2014). Because many of the pioneering
scientists had biological rather than engineering backgrounds, technical improve-
ments were also constrained by miscommunications between scientists, designers,
3 Recirculating Aquaculture Technologies 37
Aquaponics is a term that has been ‘coined’ in the 1970s, but in practice has ancient
roots – although there are still discussions about its first occurrence. The Aztec
cultivated agricultural islands known as chinampas (the earliest 1150–1350CE), in a
system considered by some to be the first form of aquaponics for agricultural use
(Fig. 3.1). In such systems, plants were raised on stable, or sometime movable and
floating islands placed in lake shallows wherein nutrient rich mud could be dredged
38 C. A. Espinal and D. Matulić
Fig. 3.1 Chinampas (floating gardens) in Central America – artificial island construction as
antecedent of aquaponic technology. (From Marzolino/Shutterstock.com)
from the chinampa canals and placed on the islands to support plant growth
(Crossley 2004).
An even earlier example of aquaponics started on the other side of the world in
south China and is believed to have spread within South East Asia where Chinese
settlers from Yunnan settled around 5 CE. Farmers cultivated and farmed rice in
paddy fields in combination with fish (FAO 2001). These polycultural farming
systems existed in many Far Eastern countries to raise fish such as oriental loach
(Misgurnus anguillicaudatus) (Tomita-Yokotani et al. 2009), swamp eel (fam.
Synbranchidae), common carp (Cyprinus carpio) and crucian carp (Carassius
carassius) (FAO 2004). In essence, however, these were not aquaponic systems
but can be best described as early examples of integrated aquaculture systems
(Gomez 2011). In the twentieth century, the first attempts to create practical, efficient
and integrated fish production systems alongside vegetables were made in the 1970s
with the work of Lewis and Naegel (Lewis and Wehr 1976; Naegel 1977; Lewis
et al. 1978). Further early systems were designed by Waten and Busch in 1984 and
Rakocy in 1989 (Palm et al. 2018).
3 Recirculating Aquaculture Technologies 39
RAS are complex aquatic production systems that involve a range of physical,
chemical and biological interactions (Timmons and Ebeling 2010). Understanding
these interactions and the relationships between the fish in the system and the
equipment used is crucial to predict any changes in water quality and system
performance. There are more than 40 water quality parameters than can be used to
determine water quality in aquaculture (Timmons and Ebeling 2010). Of these, only
a few (as described in Sects. 3.2.1, 3.2.2, 3.2.3, 3.2.4, 3.2.5, 3.2.6 and 3.2.7) are
traditionally controlled in the main recirculation processes, given that these pro-
cesses can rapidly affect fish survival and are prone to change with the addition of
feed to the system. Many other water quality parameters are not normally monitored
or controlled because (1) water quality analytics may be expensive, (2) the pollutant
to be analysed can be diluted with daily water exchange, (3) potential water sources
containing them are ruled out for use or (4) because their potential negative effects
have not been observed in practice. Therefore, the following water quality param-
eters are normally monitored in RAS.
Dissolved oxygen (DO) is generally the most important water quality parameter in
intensive aquatic systems, as low DO levels may quickly result in high stress in fish,
nitrifying biofilter malfunction and indeed significant fish losses. Commonly, stock-
ing densities, feed addition, temperature and the tolerance of the fish species to
hypoxia will determine the oxygen requirements of a system. As oxygen can be
transferred to water in concentrations higher than its saturation concentration under
atmospheric conditions (this is called supersaturation), a range of devices and
designs exist to ensure that the fish are provided with sufficient oxygen.
In RAS, DO can be controlled via aeration, addition of pure oxygen, or a
combination of these. Since aeration is only capable of raising the DO concentrations
to the atmospheric saturation point, the technique is generally reserved for lightly
loaded systems or systems with tolerant species such as tilapia or catfish. However,
aerators are also an important component of commercial RAS where the use of
expensive technical oxygen is reduced by aerating water with a low dissolved
oxygen content back to the saturation point before supersaturating the water with
technical oxygen.
There are several types of aerators and oxygenators that can be used in RAS and
these fall within two broad categories: gas-to-liquid and liquid-to-gas systems
(Lekang 2013). Gas-to-liquid aerators mostly comprise diffused aeration systems
where gas (air or oxygen) is transferred to the water, creating bubbles which
exchange gases with the liquid medium (Fig. 3.2). Other gas-to-liquid systems
include passing gases through diffusers, perforated pipes or perforated plates to
40 C. A. Espinal and D. Matulić
Compressor or Blower
Feed Gas
Fig. 3.2 Diagrams of two gas-to-liquid transfer examples: diffused aeration and Venturi injectors/
aspirators
Feed Gas
Pump Aspirator
Fig. 3.3 Diagrams of two liquid-to-gas transfer examples: the packed column aerator and surface
splashers in an enclosed tank. The packed column aerator allows water to trickle down an enclosed
vessel, usually packed with structured media, where air is forced through using a fan or blower.
Surface splashers found in pond aquaculture can also be used in enclosed atmospheres enriched
with gases – normally oxygen – for gas transfer
create bubbles using Venturi injectors which create masses of small bubbles or
devices which trap gas bubbles in the water stream such as the Speece Cone and
the U-tube oxygenator.
Liquid-to-gas aerators are based on diffusing the water into small droplets to
increase the surface area available for contact with the air, or creating an atmosphere
enriched with a mixture of gases (Fig. 3.3). The packed column aerator (Colt and
Bouck 1984) and the low-head oxygenators (LHOs) (Wagner et al. 1995) are
examples of liquid-to-gas systems used in recirculating aquaculture. However,
other liquid-to-gas systems popular in ponds and outdoor farms such as paddlewheel
aerators (Fast et al. 1999) are also used in RAS.
Considerable literature is available on gas exchange theory and the fundamentals
of gas transfer in water, and the reader is encouraged not only to consult aquaculture
and aquaculture engineering texts, but also to refer to process engineering and
wastewater treatment materials for a better understanding of these processes.
3 Recirculating Aquaculture Technologies 41
3.2.2 Ammonia
In an aqueous medium, ammonia exists in two forms: a non-ionized form (NH3) that
is toxic to fish and an ionized form (NH4+) that has low toxicity to fish. These two
form the total ammonia nitrogen (TAN), wherein the ratio between the two forms is
controlled by pH, temperature and salinity. Ammonia accumulates in the rearing
water as a product of the protein metabolism of the fish (Altinok and Grizzle 2004)
and can achieve toxic concentrations if left untreated. Of the 35 different types of
freshwater fish that have been studied, the average acute toxicity value for ammonia
is 2.79 mg NH3/l (Randall and Tsui 2002).
Ammonia has been traditionally treated in recirculation systems with nitrifying
biofilters, devices that are designed to promote microbial communities that can
oxidize ammonia into nitrate (NO3). Although the use of nitrifying biofilters is not
new, contemporary RAS has seen a streamlining of biofilter designs, with just a few,
well-studied designs having widespread acceptance. Other highly innovative tech-
niques to treat ammonia have been developed over the past few years, but are not
widely applied commercially (examples noted below).
Ammonia is oxidized in biofilters by communities of nitrifying bacteria. Nitrify-
ing bacteria are chemolithotrophic organisms that include species of the genera
Nitrosomonas, Nitrosococcus, Nitrospira, Nitrobacter and Nitrococcus (Prosser
1989). These bacteria obtain their energy from the oxidation of inorganic nitrogen
compounds (Mancinelli 1996) and grow slowly (replication occurs 40 times slower
than for heterotrophic bacteria) so are easily outcompeted by heterotrophic bacteria
if organic carbon, mostly present in biosolids suspended in the culture water, are
allowed to accumulate (Grady and Lim 1980). During RAS operation, good system
management greatly relies on minimizing suspended solids through adequate solids
removal techniques (Fig. 3.4).
Nitrifying biofilters or biofilter reactors have been roughly classified into two
main categories: suspended growth and attached growth systems (Malone and
Pfeiffer 2006). In suspended growth systems, the nitrifying bacterial communities
grow freely in the water, forming bacterial flocs which also harbour rich ecosystems
where protozoa, ciliates, nematodes and algae are present (Manan et al. 2017). With
appropriate mixing and aeration, algae, bacteria, zooplankton, feed particles and
faecal matter remain suspended in the water column and naturally flocculate
together, forming the particles that give biofloc culture systems their name (Browdy
et al. 2012). The main disadvantage of suspended growth systems is their tendency
to lose their bacterial biomass as process water flows out of the reactor, thus
requiring a means to capture and return it to the system. In attached growth systems,
solid forms (sand grains, stones, plastic elements) are used as substrates to retain the
bacteria inside the reactor and thus, do not need a post-treatment solids capture step.
Generally, attached growth systems provide more surface area for bacterial attach-
ment than suspended growth systems, and do not produce significant solids in their
outflow, which is one of the main reasons why attached growth biofilters have been
so commonly used in RAS.
42 C. A. Espinal and D. Matulić
Fig. 3.4 Nitrifying bacteria Nitrosomonas (left), and Nitrobacter (right). (Left photo: Bock et al.
1983. Right photo: Murray and Watson 1965)
Efforts have been made to classify biofilters and to document their performance in
order to help farmers and designers specify systems with a better degree of reliability
(Drennan et al. 2006; Gutierrez-Wing and Malone 2006). In recent years, the
aquaculture industry has opted for biofilter designs which have been widely studied
and thus can offer predictable performance. The moving bed bioreactor (Rusten et al.
2006), the fluidized sand filter bioreactor (Summerfelt 2006) and the fixed-bed
bioreactor (Emparanza 2009; Zhu and Chen 2002) are examples of attached growth
biofilter designs which have become standard in modern commercial RAS. Trickling
filters (Díaz et al. 2012), another popular design, have seen their popularity reduced
due to their relatively high pumping requirements and relatively large sizes.
3.2.3 Biosolids
Biosolids in RAS originate from fish feed, faeces and biofilms (Timmons and
Ebeling 2010) and are one of the most critical and difficult water quality parameters
to control. As biosolids serve as a substrate for heterotrophic bacterial growth, an
increase in their concentration may eventually result in increased oxygen consump-
tion, poor biofilter performance (Michaud et al. 2006), increased water turbidity and
3 Recirculating Aquaculture Technologies 43
even mechanical blockage of parts of the system (Becke et al. 2016; Chen et al.
1994; Couturier et al. 2009).
In RAS, biosolids are generally classified both by their size and their removal
capacity by certain techniques. Of the total fraction of solids produced in a RAS,
settleable solids are those generally bigger than 100 μm and that can be removed by
gravity separation. Suspended solids, with sizes ranging from 100 μm to 30 μm, are
those which do not settle out of suspension, but that can be removed by mechanical
(i.e. sieving) means. Fine solids, with sizes of less than 30 μm, are generally those
that cannot be removed by sieving, and must be controlled by other means such as
physico-chemical processes, membrane filtration processes, dilution or
bioclarification (Chen et al. 1994; Lee 2014; Summerfelt and Hochheimer 1997;
Timmons and Ebeling 2010; Wold et al. 2014). The techniques for controlling
settleable and suspended solids are well known and developed, and an extensive
literature exists on the subject. For example, the use of dual-drain tanks, swirl
separators, radial flow separators and settling basins is a popular means to control
settleable solids (Couturier et al. 2009; Davidson and Summerfelt 2004; De
Carvalho et al. 2013; Ebeling et al. 2006; Veerapen et al. 2005). Microscreen filters
are the most popular method for suspended solids control (Dolan et al. 2013;
Fernandes et al. 2015) and are often used in the industry to control both settleable
and suspended solids with a single technique. Other popular solids capture devices
are depth filters such as the bead filters (Cripps and Bergheim 2000) and rapid sand
filters, which are also popular in swimming pool applications. Moreover, design
guidelines to prevent the accumulation of solids in tanks, pipework, sumps and other
system components are also available in the literature (Davidson and Summerfelt
2004; Lekang 2013; Wong and Piedrahita 2000). Lastly, fine solids in RAS are
commonly treated by ozonation, bioclarification, foam fractionation or a combina-
tion of these techniques. The last few years in RAS development have focused on a
greater understanding of how to control the fine solids fraction and to understand its
effect on fish welfare and system performance.
In RAS, the control of dissolved gases does not stop with supplying oxygen to the
fish. Other gases dissolved in the rearing water may affect fish welfare if not
controlled. High dissolved carbon dioxide (CO2) concentrations in the water inhibit
the diffusion of CO2 from the blood of fish. In fish, increased CO2 in blood reduces
the blood’s pH and in turn, the affinity of haemoglobin for oxygen (Noga 2010).
High CO2 concentrations have also been associated with nephrocalcinosis, systemic
granulomas and chalky deposits in organs in salmonids (Noga 2010). CO2 in RAS
originates as a product of heterotrophic respiration by fish and bacteria. As a highly
soluble gas, carbon dioxide does not reach atmospheric equilibrium as easily as
oxygen or nitrogen and thus, it must be put in contact with high volumes of air with a
low concentration of CO2 to ensure transfer out of water (Summerfelt 2003). As a
44 C. A. Espinal and D. Matulić
general rule, RAS which are supplied with pure oxygen will require some form of
carbon dioxide stripping, while RAS which are supplied with aeration for oxygen
supplementation will not require active CO2 stripping (Eshchar et al. 2003; Loyless
and Malone 1998).
In theory, any gas transfer/aeration device open to the atmosphere will offer some
form of CO2 stripping. However, specialized carbon dioxide stripping devices
require that large volumes of air are put in contact with the process water. CO2
stripper designs have mostly focused on cascade-type devices such as cascade
aerators, trickling biofilters and, more importantly, the packed column aerator
(Colt and Bouck 1984; Moran 2010; Summerfelt 2003), which has become a
standard piece of equipment in commercial RAS operating with pure oxygen.
Although the development of packed column aeration technology has advanced
over past years, most of the research done on this device has been focused on
understanding its performance under different conditions (i.e. freshwater vs seawa-
ter) and design variations such as heights, packing types and ventilation rates. The
effect of the hydraulic loading rate (unit flow per unit area of degasser) is known to
have an effect on the efficiency of a degasser, but further research is needed to have a
better understanding of this design parameter.
Total gas pressure (TGP) is defined as the sum of the partial pressures of all the gases
dissolved in an aqueous solution. The less soluble a gas is, the more ‘room’ it
occupies in the aqueous solution and thus, the more pressure it exerts in it. Of the
main atmospheric gases (nitrogen, oxygen and carbon dioxide) nitrogen is the least
soluble (e.g. 2.3 times less soluble than oxygen and more than 90 times less soluble
than carbon dioxide). Thus, nitrogen contributes to total gas pressure more than any
other gas, but is not consumed by fish or heterotrophic bacteria, so it will accumulate
in the water unless stripped. It is also important to note that oxygen will also
contribute to high TGP if the gas transfer process does not allow excess gases to
be displaced out of the solution. A classic example of this are ponds with photoau-
totrophic activity in them. Photoautotrophs (usually plant organisms that carry out
photosynthesis) release oxygen into the water while a quiet water surface may not
provide enough gas exchange for excess gas to escape to the atmosphere and thus,
supersaturation may occur.
Fish require total gas pressures equal to atmospheric pressure. If fish breathe
water with a high total gas pressure, excess gas (generally nitrogen) exits the
bloodstream and forms bubbles, with often serious health effects for the fish
(Noga 2010). In aquaculture this is known as gas bubble disease.
Avoiding high TGP requires careful examination of all areas in the RAS where
gas transfer may occur. High-pressure oxygen injection without off-gassing
(allowing excess nitrogen to be displaced out of the water) may also contribute to
high TGP. In systems with fish which are very sensitive to TGP, the use of vacuum
3 Recirculating Aquaculture Technologies 45
degassers is an option (Colt and Bouck 1984). However, maintaining a RAS free
from areas of uncontrolled gas pressurization, using carbon dioxide strippers (which
will also strip nitrogen) and dosing technical oxygen with care, is enough to keep
TGP at safe levels in commercial RAS.
3.2.6 Nitrate
Nitrate (NO3) is the end product of nitrification and commonly the last parameter to
be controlled in RAS, due to its relatively low toxicity (Davidson et al. 2014;
Schroeder et al. 2011; van Rijn 2013). This is mostly attributed to its low perme-
ability at the fish gill membrane (Camargo and Alonso 2006). The toxic action of
nitrate is similar to that of nitrite, affecting the capacity of oxygen-carrying mole-
cules. The control of nitrate concentrations in RAS has traditionally been achieved
by dilution, by effectively controlling the hydraulic retention time or daily exchange
rate. However, the biological control of nitrate using denitrification reactors is a
growing area of research and development in RAS.
Tolerance to nitrate may vary by aquatic species and life stage, with salinity
having an ameliorating effect over its toxicity. It is important for RAS operators to
understand the chronic effects of nitrate exposure rather than the acute effects, as
acute concentrations will probably not be reached during normal RAS operation.
3.2.7 Alkalinity
The last few years have seen an increase in the number and sizes of recirculating
aquaculture farms, especially in Europe. With the increase in acceptance of the
technology, improvements over traditional engineering approaches, innovations
and new technical challenges keep emerging. The following section describes the
46 C. A. Espinal and D. Matulić
key design and engineering trends and new challenges that recirculating aquaculture
technology is facing.
The control of dissolved oxygen in modern RAS aims to increase the efficiency of
oxygen transfer and decrease the energy requirements of this process. Increasing the
oxygen transfer efficiency can be achieved by devising systems which retain oxygen
gas in contact with water for longer, while a decrease in energy requirements may be
achieved by the use of low-head oxygen transfer systems or using systems which do
not use electricity at all, such as liquid oxygen systems connected to oxygen
diffusers operating only by pressure. A defining factor of low-head oxygenators is
the relatively low dissolved concentration that can be achieved compared to high-
pressure systems. To overcome this limitation, low-head oxygenation devices are
strategically placed to treat the full recirculating flow instead of using a smaller
bypass of highly supersaturated water, thus ensuring sufficient mass transport of
oxygen. Using oxygenation devices installed in the main recirculating flow generates
savings in electricity consumption because the use of energy-intensive high-pressure
systems that are necessary to achieve high DO concentrations in small flows is
avoided. Low-head oxygenation systems may also reduce the amount of pumping
systems needed, as high-pressure oxygenation systems are commonly placed on a
bypass in the pipelines going to the fish tanks. In contrast, low-head oxygenation
devices tend to be comparatively larger because of their need to handle larger flows
and thus, their initial cost may be higher. Examples of devices that can treat the
totality of the flow include the low-head oxygenator (LHO) (Wagner et al. 1995),
operated by gravity as water is firstly pumped into a biofilter and a packed column
(Summerfelt et al. 2004), low-head oxygen cones, variants of the Speece Cone
(Ashley et al. 2008; Timmons and Losordo 1994) operated at low pressure, the
deep shaft cones (Kruger Kaldnes, Norway), also a variant of the Speece cone
designed to reach higher operating pressures by means of increased hydrostatic
pressure resulting from placing the devices lower than the fish tanks and pump
sumps, the U-tube oxygenator and its design variants such as the Farrell tube or the
patented oxygen dissolver system (AquaMAOF, Israel) and the use of diffused
oxygenation in deep fish tanks (Fig. 3.5).
Pressure
Reducing
Valve
Main flow controlling CO2, Main flow controlling CO2, Main flow controlling oxygen,
ammonia and tank turnovers ammonia and tank turnovers CO2, ammonia and tank turnovers
Fig. 3.5 Gas transfer alternatives for recirculating water returning into fish tanks. If the gas
contacting vessel allows for pressurization, oxygen can be transferred in high concentrations in
relatively small, high-pressure streams (a, b). However, oxygen at lower concentrations can be
transferred into the main recirculation loop, but for this, the oxygen transfer device must be much
larger to handle full flow of the system (c)
Fine solids are the dominant solids fraction in RAS with particles <30 μm forming
more than 90% of the total suspended solids in the culture water. Recent investiga-
tions have found that more than 94% of the solids present in the culture water of a
RAS are <20 μm in size or ‘fine’ (Fernandes et al. 2015). The accumulation of fine
solids mainly occur as larger solids bypass the mechanical filters (which are not
100% efficient) and are eventually broken down by pumps, friction with surfaces
3 Recirculating Aquaculture Technologies 49
and bacterial activity. Once solids sizes are reduced, traditional mechanical filtration
techniques are rendered useless.
In recent years, the production, control, fish welfare effects and system perfor-
mance effects of fine solids continue to be explored. The effects of fine solids on fish
welfare were initially investigated through fisheries research (Chen et al. 1994).
However, the direct effects of fine solids in RAS on fish welfare have not been
thoroughly investigated until recently. Surprisingly, separate work on rainbow trout
by Becke et al. (2016) and Fernandes et al. (2015) showed no negative welfare
effects in systems with suspended solids concentrations of up to 30 mg/l in exposure
trials lasting 4 and 6 weeks, respectively. Despite these findings, the indirect effects
of fine solids accumulation in RAS are known (Pedersen et al. 2017) and are reported
to be mostly linked to the proliferation of opportunistic microorganisms (Vadstein
et al. 2004;Attramadal et al. 2014; Pedersen et al. 2017) since fine solids provide a
high-surface area substrate for bacteria to colonize. Another important negative
effect of fine solids accumulation is the increase in turbidity, which makes visual
inspection of fish difficult and may hamper photoperiod control strategies which
require light penetration in the water column to occur. Fine solids control strategies
used in modern RAS include ozonation, protein skimming, floatation, cartridge
filtration and membrane filtration (Couturier et al. 2009; Cripps and Bergheim
2000; Summerfelt and Hochheimer 1997; Wold et al. 2014). Protein skimmers,
also known as foam fractionators, are also relatively popular fine solids control
devices, especially in marine systems (Badiola et al. 2012).
3.3.4 Ozonation
Knowledge of ozone (O3) application in RAS has existed since the 1970s and 1980s
(Summerfelt and Hochheimer 1997). However, its application has not been as
widespread as other processes such as nitrifying biofilters or mechanical filters
(Badiola et al. 2012). Aside from fine solids treatment, ozone, as a powerful oxidizer,
can be used in RAS to eliminate microorganisms, nitrite and humic substances
(Gonçalves and Gagnon 2011). Recent years have seen an increase in knowledge
about the potentials and limitations of ozone applied in both freshwater and marine
RAS. Importantly, the ozone doses that can be safely achieved to improve water
quality in both freshwater and seawater systems have been confirmed in several
publications (Li et al. 2015; Park et al. 2013, 2015; Schroeder et al. 2011;
Summerfelt 2003; Timmons and Ebeling 2010), with the conclusion that ozone
doses over recommended limits (1) do not improve water quality further and (2) may
cause negative welfare effects, especially in seawater systems where excessive
ozonation will cause the formation of toxic residual oxidants. In coldwater RAS,
ozonation requirements to achieve complete disinfection of the process flow have
been determined (Summerfelt et al. 2009).
Ozonation improves microscreen filter performance and minimizes the accumu-
lation of dissolved matter affecting the water colour (Summerfelt et al. 2009).
50 C. A. Espinal and D. Matulić
However, excessive ozonation may severely impact farmed fish by causing adverse
effects including histopathologic tissue damage (Richardson et al. 1983; Reiser et al.
2010) and alterations in feeding behaviour (Reiser et al. 2010) as well as oxidative
stress (Ritola et al. 2000, 2002; Livingstone 2003). Additionally, ozonation
by-products may be harmful. Bromate is one of these and is potentially toxic.
Tango and Gagnon (2003) showed that ozonated marine RAS have concentrations
of bromate that are likely to impair fish health. Chronic, sublethal ozone-produced
oxidants (OPO) toxicity was investigated in juvenile turbot by Reiser et al. (2011),
while rainbow trout health and welfare were assessed in ozonated and non-ozonated
RAS by Good et al. (2011). Raising rainbow trout to market size in ozonated RAS
improved fish performance without significantly impacting their health and welfare
while high OPO doses affect welfare of juvenile turbot.
3.3.5 Denitrification
less biomass (solids) and can be supplied with sulphur particles, which are cheaper
than conventional inorganic carbon sources.
VFAs are also the precursor component in the production of biopolymers such as
Polyhydroalkanoates (PHAs), used to produce biodegradable plastics (Pittmann and
Steinmetz 2013). This could hold potential for fish farms employing anaerobic
activated sludge processes to be part of the ‘biorefinery’ concept applied to waste-
water treatment plants.
Table 3.1 Primary activities associated with RAS biofiltration units and participating microorgan-
isms. (From Schreier et al. 2010)
Process Reaction Microorganism
Freshwater Marine
Nitrification
Ammonium NH4+ + 1.5O2 ! ΝO2 + Nitrosomonas Nitrosomonas sp.
oxidation 2H+ + H2O oligotropha
Nitrosomonas cryotolerans
Nitrosomonas europaea
Nitrosomonas cinnybus/
nitrosa
Nitrosococcus mobilis
Nitrite oxidation ΝO2 + H2O ! NO3 + Nitrospira
2H+ + 2e spp.
Nitrospira Nitrospira marinaa
marinaa
Nitrospira Nitrospira moscoviensisa
moscoviensisa
Denitrification
Autotrophic S2 + 1.6NO3 + 1.6H+ Thiomicrosporia denitrificans
!
(sulfide- SO42 + 0.8N2(g) + Thiothrix disciformisa
dependent) 0.8H2O
Rhodobacter litoralisa
Hydrogenophaga sp.
Heterotrophic 5CH3COO + 8NO3 + Pseudomonas fluorescens
3H+!
10HCO3 + 4N2(g) + Pseudomonas Pseudomonas stutzeri
4H2O sp.
Comamonas Pseudomonas sp.
sp.
Paracoccus denitrificans
Dissimilatory NO3 + 2H+ + 4H2 ! Various Proteobacteria and
nitrate NH4+ + 3H2O Firmicutes
Reduction to
ammonia
(DNRA)
Anaerobic NH4+ + NO2 ! N2(g) + Planctomycetes spp.
ammonium 2H2O
oxidation Brocadia sp.a
(Anammox)
Sulfate reduction SO42 + CH3COO + Desulfovibrio sp.,
3H+ !
HS + 2HCO3+ 3H+ Dethiosulfovibrio sp.,
Fusibacter sp., Bacteroides
sp.
Sulfide oxidation HS + 2O2 ! SO42 + H+ Thiomicrospira sp.
(continued)
3 Recirculating Aquaculture Technologies 53
One of the approaches for inhibiting pathogen colonization is the use of probiotic
bacteria that may compete for nutrients, produce growth inhibitors, or, quench cell-
to-cell communication (quorum sensing) that allows for settling within biofilms
(Defoirdt et al. 2007, 2008; Kesarcodi-Watson et al. 2008). Probiotic bacteria
include Bacillus, Pseudomonas (Kesarcodi-Watson et al. 2008) and Roseobacter
spp. (Bruhn et al. 2005), and bacteria related to these have also been identified in
RAS biofilters (Schreier et al. 2010) (Table 3.1). To obtain the information needed
to manage microbial stability in RAS, Rojas-Tirado et al. (2017) have identified the
factors affecting changes in the bacterial dynamics in terms of their abundance and
activity. Their studies show that bacterial activity was not a straightforward predict-
able parameter in the water phase as nitrate-N levels in identical RAS showed
unexpected sudden changes/fluctuations within one of the systems. Suspended
particles in RAS provide surface area that can be colonized by bacteria. More
particles accumulate as the intensity of recirculation increases, thus potentially
increasing the bacterial carrying capacity of the systems. Pedersen et al. (2017)
explored the relationship between total particle surface area (TSA) and bacterial
activity in freshwater RAS. They indicated a strong, positive, linear correlation
between TSA and bacterial activity in all systems with low to moderate recirculation
intensity. However, the relationship apparently ceased to exist in the systems with
the highest recirculation intensity. This is likely due to the accumulation of dissolved
nutrients sustaining free-living bacterial populations, and/or accumulation of
suspended colloids and fine particles less than 5 μm in diameter, which were not
characterized in their study but may provide significant surface area.
In RAS, various chemical compounds (mainly nitrates and organic carbon)
accumulate in the rearing water. These chemical substrata regulate the ecophysiol-
ogy of the bacterial communities on the biofilter and have an impact on its nitrifi-
cation efficiency and reliability. Michaud et al. (2014) investigated the shift of the
bacterial community structure and major taxa relative abundance in two different
biological filters and concluded that the dynamics and flexibility of the bacterial
community to adapt to influent water changes seemed to be linked with the biofilter
performance. One of the key aspects for improving the reliability and sustainability
of RAS is the appropriate management of the biofilter bacterial populations, which is
directly linked to the C (carbon) availability (Avnimelech 1999). It should be noted
that RAS have properties that may actually contribute to microbial stabilization,
including long water retention time and a large surface area of biofilters for bacterial
54 C. A. Espinal and D. Matulić
It is believed that the fundamental research in the area of microbial ecology of the
nitrification/denitrification reactor systems in RAS may provide innovations which
may alter and/or improve the reactor performance in RAS drastically. Up until now,
the microbial community in reactors is still difficult to control (Leonard et al. 2000,
2002; Michaud et al. 2006, 2009; Schreier et al. 2010; Rojas-Tirado et al. 2017) and
many of the inefficiencies of the system originate from this (Martins et al. 2010b).
3.4.1 Introduction
During the last decade, fish welfare has attracted a lot of attention, and this has led to
the aquaculture industry incorporating a number of husbandry practices and tech-
nologies specifically developed to improve this aspect. The neocortex, which in
humans is an important part of the neural mechanism that generates the subjective
experience of suffering, is lacking in fish and non-mammalian animals, and it has
been argued that its absence in fish indicates that fish cannot suffer. A strong
alternative view, however, is that complex animals with sophisticated behaviours,
such as fish, probably have the capacity for suffering, though this may be different in
degree and kind from the human experience of this state (Huntingford et al. 2006).
The UK government’s Farm and Animal Welfare Committee (FAWC) has based
their guidelines on the ‘Five Freedoms’ framework, which defines ideal states rather
than specific levels of acceptable welfare (FAWC 2014). Freedom from hunger and
thirst, discomfort, pain, injury, disease, fear and distress, as well as the freedom to
express normal behaviour, provides us with a defined framework with which to
assess welfare issues. Physical health is the most universally accepted measure of
welfare and is undoubtedly a necessary requirement for good welfare. In a compet-
itive, expanding and emerging industry, aquaculturists who incorporate welfare
considerations into their daily husbandry practices can gain a competitive advantage
and added price premium (Olesen et al. 2010) through improved consumer percep-
tion and confidence in their products. Grimsrud et al. (2013) provided evidence that
there is a high willingness to pay, among all Norwegian households, to improve the
welfare of farmed Atlantic salmon through increased resistance to diseases and
salmon lice, which may imply less use of medicines and chemicals in the production
process.
In intensive RAS, animal welfare is tightly connected to the performance of the
systems. Over the past few years, animal welfare in the RAS has been mostly studied
from the perspective of water quality and fish crowding effects on growth perfor-
mance, stress bioindicators or the development of health disorders. The main goal of
animal welfare research in the RAS has been to build and operate systems that
maximize productivity and minimize stress and mortalities. Topics of interest have
been stocking density limits (Calabrese et al. 2017), concentration limits of nitrog-
enous compounds in the rearing water (Davidson et al. 2014), concentration limits
for dissolved carbon dioxide (Good et al. 2018), the effects of ozonation (Good et al.
2011; Reiser et al. 2011) and to a lesser extent, the accumulation of recalcitrant
compounds in the RAS (van Rijn and Nussinovitch 1997) with limited water
exchanges and noise (Martins et al. 2012; Davidson et al. 2017).
3 Recirculating Aquaculture Technologies 57
Chemical Stressors
eg. pollution, low oxygen
Primary Respone(s)
eg. increase in hormone levels
Secondary Respone(s)
Physical Stressors eg. metabolic changes:
eg. capture, handling increases in glucose and/or lactate;
changes in immune function
Tertiary Respone(s)
eg. changes in whole animal health:
Perceived Stressors growth, reproduction, disease
eg. stimuli evoking a startle resistance;
response, such as sound; behavioral changes: feeding,
presence of a predator aggression
Fig. 3.6 Physical, chemical and other perceived stressors can affect fish and cause primary,
secondary and/or whole-body responses. (After Barton 2002)
3.4.2 Stress
The stress response in fish is an adaptive function in the face of a perceived threat to
homeostasis and stress physiology does not necessarily equate to suffering and
diminished welfare (Ashley 2007) (Fig. 3.6). Stress responses serve a very important
function to preserve the individual. Welfare measures in aquaculture are, therefore,
largely associated with the tertiary effects of stress response that are generally
indicative of prolonged, repeated or unavoidable stress (Conte 2004).
Stocking density is a pivotal factor affecting fish welfare in the aquaculture
industry, especially RAS where high densities in confined environments are aimed
at high productivity. Although rarely defined, stocking density is the term normally
used to refer to the weight of fish per unit volume or per unit volume in unit time of
water flow through the holding environment (Ellis et al. 2001). The concept of
minimum space for a fish is more complex than for terrestrial species as fish utilize a
three-dimensional medium (Conte 2004).
Beyond providing for the physiological needs, the FAWC (2014) recommends
that fish ‘need sufficient space to show most normal behaviour with minimal pain,
stress and fear’. Stocking density is, therefore, an area that illustrates both the
significance of species differences and the existence of a complex web of interacting
factors that affect fish welfare. Calabrese et al. (2017) have researched stocking
density limits for post-smolt Atlantic salmon (Salmosalar L.) with emphasis on
production performance and welfare wherein fin damage and cataracts were
58 C. A. Espinal and D. Matulić
observed in stocking densities of 100 kg m3 and above. However, the effect of
stocking density on measures of welfare varies between species. For instance, sea
bass (Dicentrarchus labrax) showed higher stress levels at high densities, as indi-
cated by cortisol, innate immune response and expression of stress-related genes
(Vazzana et al. 2002; Gornati et al. 2004). High stocking densities in juvenile
gilthead sea bream (S. aurata) also produce a chronic stress situation, reflected by
high cortisol levels, immunosuppression and altered metabolism (Montero et al.
1999). In contrast, Arctic charr (Salvelinus alpinus) feed and grow well when
stocked at high densities while showing a depressed food intake and growth rates
at low densities (Jorgensen et al. 1993).
Diet may also play an important role in stress sensitivity. African catfish (Clarias
gariepinus) receiving a diet with a high supplementation of ascorbic acid (vitamin C)
during early development showed a lower stress sensitivity (Merchie et al. 1997). On
the other hand, common carp (Cyprinus carpio), fed large doses of vitamin C,
showed a more pronounced cortisol (a steroid hormone released with stress) increase
in response to stress when compared to fish fed recommended levels of the vitamin
(Dabrowska et al. 1991). Tort et al. (2004) have shown that a modified diet providing
a supplementary dosage of vitamins and trace minerals to assist the immune system
may help to co-reduce some of the effects of winter disease syndrome. Other
common aquaculture diseases regarding animal welfare and stress are reviewed in
Ashley (2007).
The fundamental characteristics of good welfare are good health and absence of
disease and, with respect to aquaculture, good productivity (Turnbull and Kadri
2007; Volpato et al. 2007). While the physical health of an animal is fundamental for
good welfare (Ashley 2007; Duncan 2005), the fact that an animal is healthy does
not necessarily mean that its welfare status is adequate. Thus, welfare is a broader
and more overarching concept than the concept of health. Physiological and
behavioural measures are intrinsically linked and are dependent on one another for
a correct interpretation with regard to welfare (Dawkins 1998).
The behaviour of animals and in our case fish, represents a reaction to the
environment as fish perceive it and behaviour is therefore a key element of fish
welfare. Changes in foraging behaviour, gill ventilation activity, aggression, indi-
vidual and group swimming behaviour, stereotypic and abnormal behaviours have
been linked with acute and chronic stressors in aquaculture and can therefore be
regarded as likely indicators of poor welfare (Martins et al. 2011). Behavioural
welfare indicators have the advantage of being fast and easy to observe and therefore
are good candidates for use ‘on-farm’. Examples of behaviour that are commonly
used as an indicators of welfare are changes in food-anticipatory behaviour, feed
intake, swimming activity and ventilation rates (Huntingford et al. 2006). However,
Barreto and Volpato (2004) caution the use of ventilation frequency as an indicator
of stress in fish because although ventilation frequency is a very sensitivity response
to disturbance, it is of limited use because it does not reflect the severity of the
stimulus.
60 C. A. Espinal and D. Matulić
3.4.5 Noise
Farmed fish are cultured over long periods of time in the same tanks of the same
colour(s) and the same shape and exposed to the same, potentially harmful, back-
ground noises (Martins et al. 2012). Intensive aquaculture systems and particularly
recirculating systems utilize equipment such as aerators, air and water pumps,
blowers and filtration systems that inadvertently increase noise levels in fish culture
tanks. Sound levels and frequencies measured within intensive aquaculture systems
are within the range of fish hearing, but species-specific effects of aquaculture
production noise are not well defined (Davidson et al. 2009).
Bart et al. (2001) found that mean broadband sound pressure levels (SPL) differed
across various intensive aquaculture systems. In his study, a sound level of 135 dB re
1μPa was measured in an earthen pond near an operating aerator, whereas large
fiberglass tanks (14 m diameter) within a recirculating system had the highest SPLs
of 153 dB re 1μPa.
Field and laboratory studies have shown that fish behaviour and physiology can
be negatively impacted by intense sound. Terhune et al. (1990) have observed
decreased growth and smoltification rates of Atlantic salmon, Salmo salar, in
fiberglass tanks that had underwater sound levels 2–10 dB re 1μPa higher at
100–500 Hz than in concrete tanks. Therefore, chronic exposure to aquaculture
production noise could cause increased stress, reduced growth rates and feed con-
version efficiency and decreased survival. However, Davidson et al. (2009) found
that after 5 months of noise exposure, no significant differences were identified
between treatments for mean weight, length, specific growth rates, condition factor,
feed conversion or survival of rainbow trout, Oncorhynchus mykiss. Similar findings
are described by Wvysocki et al. (2007). However, these findings should not be
generalized across all cultured fish species, because many species, including catfish
and cyprinids, have much greater hearing sensitivity than rainbow trout and could be
affected differently by noise. For instance, Papoutsoglou et al. (2008) provided
initial evidence that music transmission under specific rearing conditions could
have enhancing effects on S. aurata growth performance, at least at specific fish
sizes. Moreover, the observed music effects on several aspects of fish physiology
(e.g. digestive enzymes, fatty acid composition and brain neurotransmitters) imply
that certain music could possibly provide even further enhancement in growth,
quality, welfare and production.
substantial and are mostly comprised of fixed costs such as rent, interest on loans,
depreciation and variable costs such as fish feed, seed (fingerlings or eggs), labour,
electricity, technical oxygen, pH buffers, electricity, sales/marketing, maintenance
costs, etc.
When comparing productivity and economics, RAS will invariably compete with
other forms of fish production and even other sources of protein production for
human consumption. This competition is likely to exert a downwards pressure on the
sale price of fish, which in turn must be high enough to make a RAS business
profitable. As in other forms of aquaculture production, reaching higher economies
of scale is generally a way to reduce the cost of production and thus obtain access to
markets. Some examples of reduction in costs of production that can be achieved
with larger facilities are:
1. Reduced transportation costs on bulk orders of feed, chemicals, oxygen.
2. Discounts on the purchase of larger quantities of equipment.
3. Access to industrial electricity rates.
4. Automation of farm processes such as process monitoring and control, feeding,
harvesting, slaughter and processing.
5. Maximization of the use of labour: The same manpower was needed to take care
of 10 tons of fish as was needed to take care of 100 tons of fish or more.
Following the increase of economies of scale in the net pen aquaculture sector,
larger RAS are being developed on scales not considered a decade ago. The last
decade has seen the construction of facilities with production capacities of thousands
of tons per year, and this sheer size increase of RAS facilities is bringing new
technical challenges, which are explored in the next section.
preventing the accumulation of metabolites and the depletion of oxygen in the tank
even further compared to older tanks which operated at higher feed burdens. Future
work will likely provide more information on the hydrodynamics of tanks with more
than 1000 m3 in volume. Other examples of enormous tanks which are currently
being used are the tanks used in the RAS 2020 systems (Kruger, Denmark) or the
Niri concept (Niri, Norway). Adoption of these new concepts using larger tanks will
play a vital role in their profitability, as long as proper hydrodynamic conditions are
achieved.
In RAS, the intensive rearing conditions can lead to sudden and catastrophic loss of
fish if the system fails. Sources of system failure may include mechanical failure of
pumping systems and RAS equipment, power outages, loss of oxygenation/aeration
systems, hydrogen sulphide build-up and release, operational accidents and more.
These risks and solutions to them need to be identified and incorporated into
operational procedures.
The increasing size of RAS operations may also mean an increased risk of
financial loss if catastrophic loss of fish occurs. On the other hand, risk-mitigation
measures and system redundancy may also increase the cost of a RAS project and
thus, designers and engineers must strike a balance between these elements.
Aside from industry and media reports, little academic research has been done on
the risk of commercial RAS ventures. Badiola et al. (2012) surveyed RAS farms and
analysed the main technical issues, finding that poor system design, water quality
problems and mechanical problems were the main risk elements affecting the
viability of RAS.
3.5.3 Economics
Debate on the economic viability of RAS focuses mostly on the high capital start-up
costs of recirculating aquaculture farms and the long lead time before fish are ready
to be marketed, as well as the perception that RAS farms have high operating costs.
De Ionno et al. (2007) studied the commercial performance of RAS farms, conclud-
ing that economic viability increases with the scale of the operation. According to
this study, farms smaller than 100 tons per year of production capacity are only
marginally profitable in the Australian context where the study took place. Timmons
and Ebeling (2010) also provide a case for achieving large economies of scale (in the
order of magnitude of thousands of tons of production per year) which allow for the
production cost reductions through vertical integration projects such as the inclusion
of processing facilities, hatcheries or feed mills. Liu et al. (2016) studied the
economic performance of a theoretical RAS farm with a capacity of 3300 tons per
3 Recirculating Aquaculture Technologies 63
year, compared to a traditional net pen farm of the same capacity. At this scale the
RAS operation reaches similar production costs compared to the net pen farm, but
the higher capital investment doubles the payback period in comparison, even when
the fish from the RAS farm are sold at a premium price. In the future, costly and strict
licensing requiring good environmental performance may increase the viability of
RAS as competitive option for the production of Atlantic salmon.
On land-based farms, fish handling is often required for various reasons: to separate
fish into weight classes, to reduce stocking densities, to transport fish across growing
departments (i.e. from a nursery to an on-growing department) or to harvest fish
when they are market ready. According to Lekang (2013), fish are handled most
effectively with active methods such as fish pumps and also with passive methods
such as the use of visual or chemical signals that allow the fish to move themselves
from one place on the farm to the next.
Summerfeltet al. (2009) studied several means to crowd and harvest salmonids
from large circular tanks using Cornell-type dual drains. Strategies included
crowding fish with purse seines, clam-shell bar crowders and herding fish between
tanks taking advantage to their innate avoidance response to carbon dioxide.
Harvesting techniques included extracting the fish through the sidewall discharge
port of a Cornell-type dual-drain tank or using an airlift to lift the crowded fish to a
dewatering box. AquaMAOF (Israel) employs swimways and tanks sharing a
common wall to passively transfer the fish through the farm, with harvesting taking
place using a pescalator (Archimedes screw pump) at the end of a swimway. The
RAS2020 concept from Kruger (Denmark) uses bar graders/crowders permanently
installed in a donut-shaped or circular raceway tank to move and crowd the fish
without the need for fish pumps.
Despite continuing developments on this topic, the increasing size of RAS farms
will keep challenging designers and operators on how to handle fish safely, eco-
nomically and without stress. The expanding range of designs, species under
production and operation intensity of RAS farms may result in various and novel
fish transport and harvest technologies.
water ecology, fluid mechanics, gas transfer, water depuration etc. apply in more or
less equal terms to aquaponics with the exception of water quality control, as plants
and fish may have specific and different requirements.
The fundamental economic realities of RAS and aquaponics are also related. Both
technologies, are capital intensive and highly technical and are affected by econo-
mies of scale, appropriate design of the components, reliance on market conditions
and the expertise of operators.
3.6.1 Welfare
In aquaponic systems, the uptake of nutrients should be maximized for the healthy
production of plant biomass but without neglecting the best welfare conditions for
the fish in terms of water quality (Yildiz et al. 2017). Measures to reduce the risks of
the introduction or spread of diseases or infection and to increase biosecurity in
aquaponics are also important. The possible impacts of allelochemicals,
i.e. chemicals released by the plants, should be also taken into account. Moreover,
the effect of diet digestibility, faeces particle size and settling ratio on water quality
should be carefully considered. There is still a lack of knowledge regarding the
relationship between the appropriate levels of minerals needed by plants, and fish
metabolism, health and welfare (Yildiz et al. 2017) which requires further research.
• Biosolids in RAS originate from fish feed, faeces and biofilms and are one of the
most critical and difficult water quality parameters to control. A multi-step
treatment system where solids of different sizes and removed via different
mechanisms, is the most common approach.
• Ozone, as a powerful oxidizer, can be used in RAS to eliminate microorganisms,
nitrite and humic substances. Ozonation improves microscreen filter performance
and minimizes the accumulation of dissolved matter affecting the water colour.
• Denitrification reactors are biological reactors which are typically operated under
anaerobic conditions and generally dosed with some type of carbon source such
as ethanol, methanol, glucose and molasses. One of the most notable applications
of denitrification systems in aquaculture is the ‘zero exchange’ RAS.
• In aquaculture production systems microbial communities play significant roles
in nutrient recycling, degradation of organic matter and treatment and control of
disease. The role of water disinfection in RAS is being challenged by the idea of
using microbially mature water to control opportunistic pathogens.
• In intensive RAS, animal welfare is tightly connected to the performance of the
systems. The main goal of animal welfare research in RAS has been to build and
operate systems that maximize productivity and minimize stress and mortalities.
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Chapter 4
Hydroponic Technologies
Abstract Hydroponics is a method to grow crops without soil, and as such, these
systems are added to aquaculture components to create aquaponics systems. Thus,
together with the recirculating aquaculture system (RAS), hydroponic production
forms a key part of the aqua-agricultural system of aquaponics. Many different
existing hydroponic technologies can be applied when designing aquaponics sys-
tems. This depends on the environmental and financial circumstances, the type of
crop that is cultivated and the available space. This chapter provides an overview of
different hydroponic types, including substrates, nutrients and nutrient solutions, and
disinfection methods of the recirculating nutrient solutions.
4.1 Introduction
Drained
Nutrient Solution
Nutrient Nutrient
Solution Solution
Fig. 4.1 Scheme of open cycle (a) and closed loop systems (b)
4 Hydroponic Technologies 79
In most cases, open loop or run-to-waste systems rather than closed loop or
recirculation systems are adopted, although in more and more European countries
the latter are mandatory. In these open systems, the spent and/or superfluous nutrient
solution is deposited into the ground and surface water bodies, or it is used in open
field cultivation. However, regarding economics and environmental concerns, soil-
less systems should be as closed as possible, i.e. where recirculation of the nutrient
solution occurs, where the substrate is reused and where more sustainable materials
are used.
The advantages of closed systems are:
– A reduction in the amount of waste material.
– Less pollution of ground and surface water.
– A more efficient use of water and fertilizers.
– Increased production because of better management options.
– Lower costs because of the savings in materials and higher production.
There are also a number of disadvantages such as:
– The required high water quality.
– High investments.
– The risk of rapid dispersal of soil-borne pathogens by the recirculating nutrient
solution.
– Accumulation of potential phytotoxic metabolites and organic substances in the
recirculating nutrient solution.
In commercial systems, the problems of pathogen dispersal are tackled by
disinfecting the water through physical, chemical and/or biological filtration tech-
niques. However, one of the main factors that hinder the use of recirculating nutrient
solution culture for greenhouse crops is the accumulation of salts in the irrigation
water. Typically, there is a steady increase in electrical conductivity (EC) due to the
accumulation of ions, which are not fully absorbed by the crops. This may be
especially true in aquaponic (AP) settings where sodium chloride (NaCl), incorpo-
rated in the fish feed, may accumulate in the system. To amend this problem, it has
been suggested that an added desalination step could improve the nutrient balance in
multi-loop AP systems (Goddek and Keesman 2018).
The intense research carried out in the field of hydroponic cultivation has led to the
development of a large variety of cultivation systems (Hussain et al. 2014). In
practical terms all of these can also be implemented in combination with
80 C. Maucieri et al.
aquaculture; however, for this purpose, some are more suitable than others (Maucieri
et al. 2018). The great variety of systems that may be used necessitates a categori-
zation of the different soilless systems (Table 4.1).
At the start of soilless cultivation in the 1970s, many substrates were tested (Wallach
2008; Blok et al. 2008; Verwer 1978). Many failed for reasons such as being too wet,
too dry, not sustainable, too expensive and releasing of toxic substances. Several
solid substrates survived: stone wool, perlite, coir (coconut fibre), peat, polyurethane
foam and bark. Solid substrate systems can be divided as follows:
Fibrous Substrates These may be organic (e.g. peat, straw and coconut fibre) or
inorganic (e.g. stone wool). They are characterized by the presence of fibres of
different sizes, which give the substrate a high water-retention capacity (60–80%)
and a modest air capacity (free porosity) (Wallach 2008). A high percentage of the
retained water is easily available for the plant, which is directly reflected in the
minimum volume of substrate per plant required to guarantee a sufficient water
supply. In these substrates there are no obvious water and salinity gradients along the
profile, and, consequently, the roots tend to grow faster, evenly and abundantly,
using the entire available volume.
4 Hydroponic Technologies 81
Granular Substrates They are generally inorganic (e.g. sand, pumice, perlite,
expanded clay) and are characterized by different particle sizes and thus textures;
they have high porosity and are free draining. Water-holding capacity is rather poor
(10–40%), and much of the water retained is not easily available to the plant (Maher
et al. 2008). Therefore, the required volume of substrate per plant is higher compared
to the fibrous ones. In granular substrates, a marked gradient of moisture is observed
along the profile and this causes the roots to develop mainly on the bottom of
containers. Smaller particle sizes, increase in the capacity for water retention,
moisture homogeneity and greater EC and a lower volume of the substrate are
required for the plant.
Substrates are usually enveloped in plastic coverings (so-called grow bags or
slabs) or inserted in other types of containers of various sizes and of synthetic
materials.
Before planting the substrate should be saturated in order to:
• Provide adequate water and nutrients supply in the entire substrate slab.
• Achieve uniform EC and pH levels.
• Expel the presence of air and make a homogeneous wetting of the material.
It is equally important for a substrate dry phase after planting to stimulate the
plants to evolve homogeneous substrate exploration by roots to obtain an abundant
and well-distributed root system at the various levels and to expose the roots to air.
Using a substrate for the second time by rewetting may be a problem because
saturation is not possible due to drain holes in the plastic envelope. In an organic
substrate (such as coir), adopting short and frequent irrigation turns, it is possible to
recover the water-retention capability to use it for the second time, more easily than
inert substrates (stone wool, perlite) (Perelli et al. 2009).
A substrate is necessary for the anchorage of the roots, a support for the plant and
also as a water-nutritional mechanism due to its microporosity and cation exchange
capacity.
Plants grown in soilless systems are characterized by an unbalanced shoot/root
ratio, demands for water, air and nutrients that are much greater than in open field
conditions. In the latter case, the growth rates are slower, and the quantities of
substrate are theoretically unlimited. To satisfy these requirements, it is necessary
to resort to substrates which, alone or in mixture, ensure optimal and stable
chemical–physical and nutritional conditions. An array of materials with different
characteristics and costs can be used as substrates as illustrated in Fig. 4.2. However,
as yet, there is no one substrate that can be used universally in all cultivation
situations.
82 C. Maucieri et al.
Peat
Organic
Coconut
Fibre
Sand
Pumice
Lapillus
Vermiculite
Substrates Inorganic
Perlite
Expanded
Clay
Stonewool
Zeolites
Expanded
Polystyrene
Synthetic
Polyurethane
Foam
Bulk Density (BD) BD is expressed by the dry weight of the substrate per unit of
volume. It enables the anchorage of the roots and offers plant support. The optimum
BD for crops in a container varies between 150 and 500 kg m3 (Wallach 2008).
Some substrates, because of their low BD and their looseness, as is the case of perlite
(ca. 100 kg m3), polystyrene in granules (ca. 35 kg m3) and non-compressed
sphagnum peat (ca. 60 kg m3), are not suitable for use alone, especially with plants
that grow vertically.
4 Hydroponic Technologies 83
Table 4.2 Main chemical–physical characteristics of peats and coconut fibre. (dm ¼ dry matter)
Raised bogs Fen bogs
Characteristics Blond Brown Black Coconut fibre (coir)
Organic matter (% dm) 94–99 94–99 55–75 94–98
Ash (% dm) 1–6 1–6 23–30 3–6
Total porosity (% vol) 84–97 88–93 55–83 94–96
Water-retention capacity (% vol) 52–82 74–88 65–75 80–85
Free porosity (% vol) 15–42 6–14 6–8 10–12
Bulk density (kg m3) 60–120 140–200 320–400 65–110
CEC (meq%) 100–150 120–170 80–150 60–130
Total nitrogen (% dm) 0.5–2.5 0.5–2.5 1.5–3.5 0.5–0.6
C/N 30–80 20–75 10–35 70–80
Calcium (% dm) <0.4 <0.4 >2 –
pH (H2O) 3.0–4.0 3.0–5.0 5.5–7.3 5.0–6.8
Source: Enzo et al. (2001)
Porosity The ideal substrate for potted crops should have a porosity of at least 75%
with variable percentages of macropores (15–35%) and micropores (40–60%)
depending on the cultivated species and the environmental and crop conditions
(Wallach 2008; Blok et al. 2008; Maher et al. 2008). In small-sized containers,
total porosity should reach 85% of the volume (Bunt 2012). The structure should be
stable over time and should resist compaction and the reduction of volume during
dehydration phases.
Water-Holding Capacity Water-holding capacity ensures adequate levels of sub-
strate moisture for crops, without having to resort to frequent irrigations. However,
the water-holding capacity must not be too high in order to avoid root asphyxia and
too much cooling. The water available for the plant is calculated by the difference
between the quantity of water at the retention capacity and that retained at the wilting
point. This should be around 30–40% of the apparent volume (Kipp et al. 2001).
Finally, it must be considered that with the constant increase of the root system
biomass during growth, the free porosity in the substrate is gradually reduced and the
hydrological characteristics of the substrate are modified.
Cation Exchange Capacity (CEC) CEC is a measure of how many cations can be
retained on substrate particle surfaces. In general, organic materials have a higher
CEC and a higher buffer capability than mineral ones (Wallach 2008; Blok et al.
2008) (Table 4.2).
pH A suitable pH is required to suit the needs of the cultivated species. Substrates
with a low pH are more suitable for crops in containers, as they are more easily
modified towards the desired levels by adding calcium carbonate and also because
they meet the needs of a wider number of species. Moreover, during cultivation the
pH value tends to rise due to irrigation with water rich in carbonates. The pH may
also vary in relation to the type of fertilizer used. It is more difficult to correct an
alkaline substrate. This can however be achieved by adding sulphur or
84 C. Maucieri et al.
The choice of substrates ranges from products of organic or mineral origin which are
present in nature and which are subjected to special processing (e.g. peat, perlite,
vermiculite), to those of organic origin derived from human activities (e.g. waste or
by-products of agricultural, industrial and urban activities) and of industrial origin
obtained by synthesis processes (e.g. polystyrene).
This category includes natural organic substrates, including residues, waste and
by-products of organic nature derived from agricultural (manure, straw, etc.) or,
for example, industrial, by-products of the wood industry, etc. or from urban
settlements, e.g. sewage sludge, etc. These materials can be subjected to additional
processing, such as extraction and maturation.
All the materials that can be used in hydroponics can also be used in
AP. However, as the bacterial load in an AP solution may be higher than in
4 Hydroponic Technologies 85
Coconut Fibre
Coconut fibre (coir) is obtained from removing the fibrous husks of coconuts and is a
by-product of the copra (coconut oil production) and fibre extraction industry, and is
composed almost exclusively of lignin. Before use, it is composted for 2–3 years,
and then it is dehydrated and compressed. Prior to its use, it must be rehydrated by
adding up to 2–4 times of its compressed volume with water. Coconut fibre
possesses chemical–physical characteristics that are similar to blond peat
(Table 4.2), but with the advantages of having a higher pH. It also has a lower
environmental impact than peat (excessive exploitation of peat bogs) and stone wool
where there are problems with disposal. This is one of the reasons why it is
increasingly preferred in soilless systems (Olle et al. 2012; Fornes et al. 2003).
Wood-Based Substrates
Organic substrates which are derived from wood or its by-products, such as bark,
wood chips or saw dust, are also used in global commercial plant production (Maher
et al. 2008). Substrates based on these materials generally possess good air content
and high saturated hydraulic conductivities. The disadvantages can include low
water-retention capacities, insufficient aeration caused by microbial activity, inap-
propriate particle-size distribution, nutrient immobilization or negative effects due to
salt and toxic compound accumulations (Dorais et al. 2006).
This category includes natural materials (e.g. sand, pumice) and mineral products
derived from industrial processes (e.g. vermiculite, perlite) (Table 4.3).
Sand
Sands are natural inorganic material with particles between 0.05 and 2.0 mm
diameter, originating from the weathering of different minerals. The chemical
composition of sands may vary according to origin, but in general, it is constituted
by 98.0–99.5% silica (SiO2) (Perelli et al. 2009). pH is mainly related to the
carbonate content. Sands with lower calcium carbonate content and pH 6.4–7.0 are
better suited as substrate material because they do not influence the solubility of
phosphorus and some microelements (e.g. iron, manganese). Like all mineral-origin
substrates, sands have a low CEC and low buffering capability (Table 4.3). Fine
sands (0.05–0.5 mm) are the most suitable for use in hydroponic systems in mixtures
10–30% by volume with organic materials. Coarse sands (>0.5 mm) can be used in
order to increase the drainage capacity of the substrate.
Pumice
Pumice comprises aluminium silicate of volcanic origin, being very light and porous,
and may contain small amounts of sodium and potassium and traces of calcium,
magnesium and iron depending on the place of origin. It is able to retain calcium,
magnesium, potassium and phosphorus from the nutrient solutions and to gradually
release these to the plant. It usually has a neutral pH, but some materials may have
4 Hydroponic Technologies 87
Table 4.3 Main chemical–physical characteristics of inorganic substrates used in soilless systems
Water-
Bulk Total Free retention CEC
density porosity porosity capacity (meq EC
Substrates (kg m3) (%vol) (%vol) (%vol) %) (mS cm1) pH
Sand 1400–1600 40–50 1–20 20–40 20–25 0.10 6.4–7.9
Pumice 450–670 55–80 30–50 24–32 – 0.08–0.12 6.7–9.3
Volcanic 570–630 80–90 75–85 2–5 3–5 – 7.0–8.0
tuffs
Vermiculite 80–120 70–80 25–50 30–55 80–150 0.05 6.0–7.2
Perlite 90–130 50–75 30–60 15–35 1.5–3.5 0.02–0.04 6.5–7.5
Expanded 300–700 40–50 30–40 5–10 3–12 0.02 4.5–9.0
clay
Stone wool 85–90 95–97 10–15 75–80 – 0.01 7.0–7.5
Expanded 6–25 55 52 3 – 0.01 6.1
Polystyrene
Source: Enzo et al. (2001)
excessively high pH, good free porosity but low water-retention capacity
(Table 4.3). The structure however tends to deteriorate fairly quickly, due to the
easy breaking up of the particles. Pumice, added to peat, increases the drainage and
aeration of the substrate. For horticulture use, pumice particles from 2 to 10 mm in
diameter are preferred (Kipp et al. 2001).
Volcanic Tuffs
Tuffs derive from volcanic eruptions, with particles ranging between 2 and 10 mm
diameter. They may have a bulk density ranging between 850 and 1100 kg m3
and a water-retention capacity between 15% and 25% by volume (Kipp et al.
2001).
Vermiculite
Vermiculite comprises hydrous phyllosilicates of magnesium, aluminium and iron,
which in the natural state have a thin lamellar structure that retains tiny drops of
water. Exfoliated vermiculite is commonly used in the horticultural industry and
is characterized by a high buffer capability and CEC values similar to those of the
best peats (Table 4.3), but, compared to these, it has a higher nutrient availability
(5–8% potassium and 9–12% magnesium) (Perelli et al. 2009). NH4+ is especially
strongly retained by vermiculite; the activity of the nitrifying bacteria, however,
allows the recovery of part of the fixed nitrogen. Similarly, vermiculite binds over
75% of phosphate in an irreversible form, whereas it has low absorbent capacity for
Cl, NO3 and SO4. These characteristics should be carefully assessed when
vermiculite is used as a substrate. The vermiculite structure is not very stable because
of a low compression resistance and tends to deteriorate over time, reducing
88 C. Maucieri et al.
water drainage. It can be used alone; however, it is preferable to mix it with perlite
or peat.
Perlite
Perlite comprises aluminium silicate of volcanic origin containing 75% SiO2 and
13% Al2O3. The raw material is crushed, sieved, compressed and heated to
700–1000 C. At these temperatures, the little water contained in the raw material
turns into vapour by expanding the particles into small whitish-grey aggregates
which, unlike vermiculite, have a closed cell structure. It is very light and possesses
high free porosity even after the soaking. It contains no nutrients, has negligible CEC
and is virtually neutral (Table 4.3) (Verdonk et al. 1983). pH, however, can vary
easily, because the buffer capacity is insignificant. pH ought to be controlled via the
quality of the irrigation water and should not fall below 5.0 in order to avoid the
phytotoxic effects of the aluminium. The closed cell structure allows water to be held
only on the surface and in the spaces between the agglomerations, so the water-
retention capacity is variable in relation to the dimensions of the agglomerations. It is
marketed in different sizes, but the most suitable for horticulture are 2–5 mm
diameter. It can be used as a substrate in rooting beds, because it ensures good
aeration. In mixtures with organic materials, it enhances the softness, permeability
and aeration of the substrate. Perlite can be reused for several years as long as it is
sterilized between uses.
Expanded Clay
Expanded clay is obtained by treating clay powder at about 700 C. Stable aggre-
gates are formed, and, depending on the used clay material, they have variable values
with regard to CEC, pH and bulk density (Table 4.3). Expanded clay can be used in
mixtures with organic materials in the amounts of about 10–35% by volume, to
which it provides more aeration and drainage (Lamanna et al. 1990). Expanded clays
with pH values above 7.0 are not suitable for use in soilless systems.
Stone Wool
Stone wool is the most used substrate in soilless cultivation. It originates from the
fusion of aluminium, calcium and magnesium silicates and carbon coke at
1500–2000 C. The liquefied mixture is extruded in 0.05 mm diameter strands
and, after compression and addition of special resins, the material assumes a very
light fibrous structure with a high porosity (Table 4.3).
Stone wool is chemically inert and, when added to a substrate, it improves its
aeration and drainage and also offers an excellent anchorage for plant roots. It is used
alone, as a sowing substrate and for soilless cultivation. The slabs used for the
cultivation can be employed for several production cycles depending on quality, as
long as the structure is able to guarantee enough porosity and oxygen availability for
root systems. Usually, after several crop cycles, the greater part of substrate porosity
is filled with old, dead roots, and this is due to the compaction of the substrate over
time. The result is a then a reduced depth of substrate where irrigation strategies may
need adaptation.
4 Hydroponic Technologies 89
Zeolites
Zeolites comprise hydrated aluminium silicates characterized by the capacity to
absorb gaseous elements; they are high in macro- and microelements, they have
high absorbent power and they have high internal surface (structures with 0.5 mm
pores). This substrate is of great interest as it absorbs and slowly releases K+ and
NH4+ ions, whilst it is not able to absorb Cl and Na+, which are hazardous to plants.
Zeolites are marketed in formulations which differ in the N and P content and which
can be used in seed sowing, for the rooting of cuttings or during the cultivation phase
(Pickering et al. 2002).
Mixed substrates can be useful to reduce overall substrate costs and/or to improve
some characteristics of the original materials. For example, peat, vermiculite and coir
can be added to increase water-retention capacity; perlite, polystyrene, coarse sand
and expanded clay to increase free porosity and drainage; blonde peat to raise the
acidity; higher quantities of organic material or suitable amounts of clay soil to
increase CEC and buffer capability; and low decomposable substrates for increased
90 C. Maucieri et al.
durability and stability. The characteristics of the mixtures rarely represent the
average of the components because with the mixing the structures are modified
between the individual particles and consequently the relationship of physical and
chemical characteristics. In general, mixtures with a low nutrient content are pref-
erable, in order to be able to better manage cultivation. The right relationship among
the different constituents of a mixture also varies with the environmental conditions
in which it operates. At high temperatures it is rational to use components that
possess a higher water-retention capacity and do not allow fast evaporation
(e.g. peat) and, at the same time, are resilient to decomposition. In contrast, in
humid environments, with low solar radiation, the components characterized by
high porosity are preferred to ensure good drainage. In this case, it will be necessary
to add coarse substrates such as sand, pumice, expanded clay and expanded poly-
styrene (Bunt 2012).
Deep flow technique (DFT), also known as deep water technique, is the cultivation
of plants on floating or hanging support (rafts, panels, boards) in containers filled
with 10–20 cm nutrient solution (Van Os et al. 2008) (Fig. 4.3). In AP this can be up
to 30 cm. There are different forms of application that can be distinguished mainly
by the depth and volume of the solution, and the methods of recirculation and
oxygenation.
One of the simplest systems comprises 20–30 cm deep tanks, which can be
constructed of different materials and waterproofed with polyethylene films. The
tanks are equipped with floating rafts (several types are available from suppliers) that
serve to support the plants above the water whilst the plants’ roots penetrate the
water. The system is particularly interesting as it minimizes costs and management.
For example, there is a limited need for the automation of the control and correction
DFT
of the nutrient solution, particularly in short duration crops such as lettuce, where the
relatively high volume of solution facilitates the replenishment of the nutrient
solution only at the end of each cycle, and only the oxygen content needs to be
monitored periodically. Oxygen levels should be above 4–5 mg L1; otherwise,
nutrient deficiencies may appear due to root systems uptake low performance.
Circulation of the solution will normally add oxygen, or Venturi systems can be
added which dramatically increase air into the system. This is especially important
when water temperatures are greater than 23 C, as such high temperatures may
stimulate lettuce bolting.
The NFT technique is used ubiquitously and can be considered the classic hydro-
ponic cultivation system, where a nutrient solution flows along and circulates in
troughs with a 1–2 cm layer of water (Cooper 1979; Jensen and Collins 1985; Van
Os et al. 2008) (Fig. 4.4). The recirculation of the nutrient solution and the absence
of substrate represent one of the main advantages of the NFT system. An additional
advantage is its great potential for automation to save on labour costs (planting &
harvesting) and the opportunity to manage the optimal plant density during crop
cycle. On the other hand, the lack of substrate and low water levels makes the NFT
vulnerable to the failure of pumps, due to e.g. clogging or a failure in the power
supply. Temperature fluctuations in the nutrient solution can cause plant stress
followed by diseases.
Fig. 4.4 Illustration of NFT system (left) and a multilayer NFT trough, developed and marketed by
New Growing Systems (NGS), Spain (right)
92 C. Maucieri et al.
The development of the root system, part of which remains suspended in air
above the nutrient flow and which is exposed to an early ageing and loss of
functionality, represents a major constraint as it prevents the production of long-
cycle crops (over 4–5 months). Because of its high susceptibility to temperature
variations, this system is not suitable for cultivation environments characterized by
high levels of irradiation and temperature (e.g. southern areas of the Mediterranean
basin). However, in response to these challenges, a multilayer NFT trough has been
designed which allows for longer production cycles without clogging problems (NGS).
It is made of a series of interconnected layers placed in a cascade, so that even in strong
rooting plant species, such as tomatoes, the nutrient solution will still find its way to the
roots by by-passing the root-clogged layer via a lower positioned layer.
The aeroponic technique is mainly aimed at smaller horticultural species, and has not
yet been widely used due to the high investment and management costs. Plants are
supported by plastic panels or by polystyrene, arranged horizontally or on inclined
tops of growing boxes. These panels are supported by a structure made with inert
materials (plastic, steel coated with plastic film, polystyrene boards), in order to form
closed boxes where the suspended root system can develop (Fig. 4.5).
The nutrient solution is directly sprayed on the roots, which are suspended in the
box in air, with static sprinklers (sprayers), inserted on pipes housed inside the box
module. The spray duration is from 30 to 60 s, whilst the frequency varies depending
on the cultivation period, the growth stage of the plants, the species and the time of
day. Some systems use vibrating plates to create micro droplets of water which form
a steam which condenses on the roots. The leachate is collected on the bottom of the
box modules and conveyed to the storage tank, for reuse.
Amongst the main mechanisms involved in plant nutrition, the most important is the
absorption which, for the majority of the nutrients, takes place in ionic form
following the hydrolysis of salts dissolved in the nutrient solution.
Active roots are the main organ of the plant involved in nutrient absorption.
Anions and cations are absorbed from the nutrient solution, and, once inside the
plant, they cause the protons (H+) or hydroxyls (OH) to exit which maintains the
balance between the electric charges (Haynes 1990). This process, whilst
maintaining the ionic equilibrium, can cause changes in the pH of the solution in
relation to the quantity and quality of the nutrients absorbed (Fig. 4.6).
The practical implications of this process for the horticulturist are two-fold: to
provide adequate buffer capability to the nutrient solution (adding bicarbonates if
needed) and to induce slight pH changes with the choice of fertilizer. The effect of
fertilizers on the pH relates to the different chemical forms of the used compounds.
H2PO4- K+
SO4-- Ca++
NO3 - NH4+
OH- H+
pH increase pH decrease
In the case of N, for example, the most commonly used form is nitric nitrogen
(NO3), but when the pH should be lowered, nitrogen can be supplied as ammonium
nitrogen (NH4+). This form, when absorbed, induces the release of H+ and conse-
quently an acidification of the medium.
Climatic conditions, especially air and substrate temperature and relative humid-
ity, exert a major influence on the absorption of nutrients (Pregitzer and King 2005;
Masclaux-Daubresse et al. 2010; Marschner 2012; Cortella et al. 2014). In general,
the best growth occurs where there are few differences between substrate and air
temperature. However, persistently high temperature levels in the root system have a
negative effect. Sub-optimal temperatures reduce the absorption of N (Dong et al.
2001). Whilst NH4+ is effectively used at optimum temperatures, at low tempera-
tures, the bacterial oxidation is reduced, causing accumulation within the plant that
can produce symptoms of toxicity and damage to the root system and the aerial
biomass. Low temperatures at the root level also inhibit the assimilation of K and P, as
well as the P translocation. Although the available information regarding the effect of
low temperatures on the absorption of micronutrients is less clear, it appears that Mn,
Zn, Cu, and Mo uptake are most affected (Tindall et al. 1990; Fageria et al. 2002).
The appropriate management of plant nutrition must be based on basic aspects that
are influenced by uptake and use of macro, and micro-nutrients (Sonneveld and
Voogt 2009). Macro-nutrients are needed in relatively large amounts, whilst micro-
nutrients or trace elements are needed in small amounts. Furthermore, nutrient
availability to the plant in the case of the soilless systems presents more or less
consistent phenomena of synergy and antagonism (Fig. 4.7).
Nitrogen (N) Nitrogen is absorbed by plants to produce amino acids, proteins,
enzymes and chlorophyll. The most used nitrogen forms for plant fertilization are
nitrate and ammonium. Nitrates are quickly absorbed by the roots, are highly
movable inside the plants and can be stored without toxic effects. Ammonium can
be absorbed by plants only in low quantities and cannot be stored at high quantities
because it exerts toxic effects. Quantities higher than 10 mg L1 inhibit plant
calcium and copper uptake, increase the shoot growth compared to root growth
and result in a strong green colour of the leaves. Further excesses in ammonia
concentration result in phytotoxic effects such as chlorosis along the leaves’ mar-
gins. Excess in nitrogen supply causes high vegetative growth, increase of crop cycle
length, strong green leaf colour, low fruit set, high content of water in the tissues, low
tissue lignification and high tissue nitrate accumulation. Commonly, nitrogen defi-
ciency is characterized by a pale green colour of the older leaves (chlorosis), reduced
growth and senescence advance.
4 Hydroponic Technologies 95
Antagonism Synergy
Mn Mn
K Ca K Ca
Fe Cu Fe Cu
P Mg P Mg
B Mo B Mo
NH4+ Zn NH4+ Zn
Fig. 4.7 Nutrients synergies and antagonisms amongst ions. Connected ions present synergistic or
antagonistic relationship according to the direction of the arrow
Potassium (K) Potassium is fundamental for cell division and extension, protein
synthesis, enzyme activation and photosynthesis and also acts as a transporter of
other elements and carbohydrates through the cell membrane. It has an important
role in keeping the osmotic potential of the cell in equilibrium and regulating the
stomatal opening. The first signs of deficiency are manifested in the form of
yellowish spots that very quickly necrotize on the margins of the older leaves.
Potassium deficient plants are more susceptible to sudden temperature drops, water
stress and fungal attacks (Wang et al. 2013).
Phosphorus (P) Phosphorus stimulates roots development, the rapid growth of buds
and flower quantity. P is absorbed very easily and can be accumulated without
damage to the plant. Its fundamental role is linked to the formation of high-energy
compounds (ATP) necessary for plant metabolism. The average quantities requested
by plants are rather modest (10–15% of the needs of N and K) (Le Bot et al. 1998).
However, unlike what occurs in soil, P is easily leachable in soilless crops. The
absorption of P appears to be reduced by low substrate temperatures (< 13 C) or at
increasing pH values (> 6.5) which can lead to deficiency symptoms (Vance et al.
2003). Under these conditions a temperature increase and/or pH reduction is more
effective than additional amendments of phosphorus fertilizers. P excess can reduce
or block the absorption of some other nutrients (e.g. K, Cu, Fe) (Fig. 4.7). Phos-
phorus deficiency manifests in a green-violet colour of the older leaves, which may
follow chlorosis and necrosis in addition to the stunted growth of the vegetative
apex. However, these symptoms are non-specific and make P deficiencies difficult to
be identified (Uchida 2000).
96 C. Maucieri et al.
Chlorine (Cl) Chlorine has been recently considered a micro-nutrient, even if its
content in plants (0.2–2.0% dw) is quite high. It is easily absorbed by the plant and is
very mobile within it. It is involved in the photosynthetic process and the regulation
of the stomata opening. Deficiencies, which are rather infrequent, occur with typical
symptoms of leaves drying out, especially at the margins. Much more widespread is
the damage due to an excess of Cl that leads to conspicuous plant shrinkage which is
relative to the different sensitivities of different species. To avoid crop damage, it is
always advisable to check the Cl content in the water used to prepare nutrient
solutions and choose suitable fertilizers (e.g. K2SO4 rather than KCl).
Sodium (Na) Sodium, if in excess, is harmful to plants, as it is toxic and interferes
with the absorption of other ions. The antagonism with K (Fig. 4.7), for example, is
not always harmful because in some species (e.g. tomatoes), it improves the fruit
taste, whereas in others (e.g. beans), it can reduce plant growth. Similar to Cl, it is
important to know the concentration in the water used to prepare the nutrient solution
(Sonneveld and Voogt 2009).
Manganese (Mn) Manganese forms part of many coenzymes and is involved in the
extension of root cells and their resistance to pathogens. Its availability is controlled
by the pH of the nutrient solution and by competition with other nutrients (Fig. 4.7).
Symptoms of deficiency are similar to those of the Fe except for the appearance of
slightly sunken areas in the interveinal areas (Uchida 2000). Corrections can be
made by adding MnSO4 or by lowering the pH of the nutrient solution.
Boron (B) Boron is essential for fruit setting and seed development. The absorption
methods are similar to those already described for Ca with which it can compete. The
pH of the nutrient solution must be below 6.0 and the optimal level seems to be
between 4.5 and 5.5. Symptoms of deficiency can be detected in the new structures
that appear dark green, the young leaves greatly increase their thickness and have a
leathery consistency. Subsequently they can appear chlorotic and then necrotic, with
rusty colouring.
Zinc (Zn) Zinc plays an important role in certain enzymatic reactions. Its absorption
is strongly influenced by the pH and the P supply of the nutrient solution. pH values
between 5.5 and 6.5 promote the absorption of Zn. Low temperature and high P
levels reduce the amount of zinc absorbed by the plant. Zinc deficiencies occur
rarely, and are represented by chlorotic spots in the interveinal areas of the leaves,
very short internodes, leaf epinasty and poor growth (Gibson 2007).
Copper (Cu) Copper is involved in respiratory and photosynthetic processes. Its
absorption is reduced at pH values higher than 6.5, whilst pH values lower than 5.5
may result in toxic effects (Rooney et al. 2006). High levels of ammonium and
phosphorus interact with Cu reducing the availability of the latter. The excessive
presence of Cu interferes with the absorption of Fe, Mn and Mo. The deficiencies are
manifested by interveinal chlorosis which leads to the collapse of the leaf tissues that
look like desiccated (Gibson 2007).
98 C. Maucieri et al.
Since the development of soilless horticulture systems in the 1970s (Verwer 1978;
Cooper 1979), different nutrient solutions have been developed and adjusted
according to the growers’ preferences (Table 4.4; De Kreij et al. 1999). All mixes
follow the principles of excess availability of all elements to prevent deficiencies and
balance between (bivalent) cations to avoid competition between cations in plant
nutrient uptake (Hoagland and Arnon 1950; Steiner 1961; Steiner 1984; Sonneveld
and Voogt 2009). Commonly, the EC is allowed to rise in the root zone to a limited
degree. In tomatoes, for example, the nutrient solution typically has an EC of
ca. 3 dS m1, whilst in the root zone in the stone wool slabs, the EC may rise to
4–5 dS m1. However, in northern European countries, for the first irrigation of new
stone wool slabs at the beginning of the production cycle, the nutrient solution may
have an EC as high as 5 dS m1, saturating the stone wool substrate with ions up to
an EC of 10 dS m1, which will subsequently be flushed after 2 weeks. To provide
sufficient flushing of the root zone, in a typical drip-irrigation stone wool slab
system, about 20–50% of the dosed water is collected as drainage water. The
drainage water is then recycled, filtered, mixed with fresh water and topped up
with nutrients for use in the next cycle (Van Os 1994).
In tomato production, increasing the EC can be applied to enhance lycopene
synthesis (promoting the bright red coloration of the fruits), total soluble solids
(TSS) and fructose and glucose content (Fanasca et al. 2006; Wu and Kubota 2008).
Furthermore, tomato plants have higher absorption rates for N, P, Ca and Mg and
low absorption of K during the early (vegetative) stages. Once the plants start
developing fruits, leaf production is slowed down leading to a reduction in N and
Ca requirements, whilst K requirement increases (e.g. Zekki et al. 1996; Silber,
Bar-Tal 2008). In lettuce, on the other hand, an increased EC may promote tip-burn
disease during hot growing conditions. Huett (1994) showed a significant decrease
in the number of leaves with tip-burn disease per plant when the EC was dropped
from 3.6 to 0.4 dS m1, as well as when the nutrient formulation K/Ca was reduced
from 3.5:1 to 1.25:1. In AP the management of nutrients is more difficult than in
hydroponics since they mainly depend on fish stock density, feed type and feeding
rates.
4 Hydroponic Technologies 99
nitric acid, about 0.5 mmol L1 that can be maintained as a pH buffer in the nutrient
solution. Phosphoric and sulphuric acid can also be possibly used to compensate pH,
but both will rapidly give a surplus of H2PO4 or SO42 in the nutrient solution. In
AP systems nitric acid (HNO3) and potassium hydroxide (KOH) can be also used to
regulate pH and at same time supply macronutrients in the system (Nozzi et al.
2018).
present in the water, in order to reduce its effect, which is particularly negative for
some crops, it will be necessary to increase the amount of NO3 and Ca and
possibly decrease the K, keeping the EC at the same level.
2. Nutrient requirement calculations should be obtained by subtracting the values of
the chemical elements of the water from the chemical elements defined above. For
example, the established need for Mg of peppers (Capsicum sp.) is 1.5 mM L1,
having the water at 0.5 mM L1, and 1.0 mM L1 of Mg should be added to the
water (1.5 requirement – 0.5 water supply ¼ 1.0).
3. Choice and calculation of fertilizers and acids to be used. For example, having to
provide Mg, as in the example of point 2 above, MgSO4 or Mg(NO3)2 can be
used. A decision will be made taking into account the collateral contribution of
sulphate or nitrate as well.
During their life cycle, plants need several essential macro- and microelements for
regular development (boron, calcium, carbon, chlorine, copper, hydrogen, iron,
magnesium, manganese, molybdenum, nitrogen, oxygen, phosphorous, potassium,
sulphur, zinc), usually absorbed from the nutrient solution (Bittsanszky et al. 2016).
The nutrient concentration and ratio amongst them are the most important variables
capable to influence plant uptake. In AP systems fish metabolic wastes contain
nutrients for the plants, but it must be taken into account, especially at commercial
scales, that the nutrient concentrations supplied by the fish in AP systems are
significantly lower and unbalanced for most nutrients compared to hydroponic
systems (Nicoletto et al. 2018). Usually, in AP, with appropriate fish stocking
rates, the levels of nitrate are sufficient for good plant growth, whereas the levels
of K and P are generally insufficient for maximum plant growth. Furthermore,
calcium and iron could also be limited. This can reduce the crop yield and quality
and so nutrient integration should be carried out to support an efficient nutrient reuse.
Microbial communities play a crucial role in the nutrient dynamic of AP systems
(Schmautz et al. 2017), converting ammonium to nitrate, but also contributing to the
processing of particulate matter and dissolved waste in the system (Bittsanszky et al.
2016). Plant uptake of N and P represents only a fraction of the amount removed
from the water (Trang and Brix 2014), indicating that microbial processes in the root
zone of the plants, and in the substrate (if present) and throughout the whole system,
play a major role.
The composition of fish feeds depends on the type of fish and this influences
nutrient release from fish’s metabolic output. Typically, fish feed contains an energy
source (carbohydrates and/or lipids), essential amino acids, vitamins, as well as other
organic molecules that are necessary for normal metabolism but some that the fish’s
4 Hydroponic Technologies 103
cells cannot synthesize. Furthermore, it must be taken into account that a plant’s
nutritional requirements vary with species (Nozzi et al. 2018), variety, life cycle
stage, day length and weather conditions and that recently (Parent et al. 2013; Baxter
2015), the Liebig’s law (plant growth is controlled by the scarcest resource) has been
superseded by complex algorithms that consider the interactions between the indi-
vidual nutrients. Both these aspects do not allow a simple evaluation of the effects of
changes in nutrient concentrations in hydroponic or AP systems.
The question thus arises whether it is necessary and effective to add nutrients to
AP systems. As reported by Bittsanszky et al. (2016), AP systems can only be
operated efficiently and thus successfully, if special care is taken through the
continuous monitoring of the chemical composition of the recirculating water for
adequate concentrations and ratios of nutrients and of the potentially toxic compo-
nent, ammonium. The necessity to add nutrients depends on plant species and
growth stage. Frequently, although fish density is optimal for nitrogen supply, the
addition of P and K with mineral fertilizers, at least, should be carried out (Nicoletto
et al. 2018). In contrast to, for example, lettuce, tomatoes which need to bear fruit,
mature and ripen, need supplemental nutrients. In order to calculate these needs, a
software can be used, such as HydroBuddy which is a free software (Fernandez
2016) that is used to calculate the amount of required mineral nutrient supplements.
Disinfection of the circulating nutrient solution should take place continuously. All
drain returned (10–12 h during daytime) has to be treated within 24 h. For a
greenhouse of 1000 m2 in a substrate cultivation (stone wool, coir, perlite), a
disinfection capability of about 1–3 m3 per day is needed to disinfect an estimated
needed surplus of 30% of the water supplied with drip irrigation to tomato plants
during a 24-h period in summer conditions. Because of the variable return rate of
drain water, a sufficiently large catchment tank for drain water is needed in which the
water is stored before it is pumped to the disinfection unit. After disinfection another
tank is required to store the clean water before adjusting EC and pH and blending
with new water to supply to the plants. Both tanks have an average size of 5 m3 per
1000 m2. In a nutrient film system (NFT), about 10 m3 per day should be disinfected
daily. It is generally considered that such a capacity is uneconomical to disinfect
(Ruijs 1994). DFT requires similar treatment. This is the main reason why NFT and
DFT production units do not normally disinfect the nutrient solution. Disinfection is
carried out either by non-chemical or chemical methods as follows:
In general these methods do not alter the chemical composition of the solution, and
there is no build-up of residuals:
1. Heat treatment. Heating the drain water to temperatures high enough to eradicate
bacteria and pathogens is the most reliable method for disinfection. Each type of
organism has its own lethal temperature. Non-spore-forming bacteria have lethal
temperatures between 40 and 60 C, fungi between 40 and 85 C, nematodes
between 45 and 55 C and viruses between 80 and 95 C (Runia et al. 1988) at an
exposure time of 10 s. Generally, the temperature set point of 95 C is high
enough to kill most of the organisms that are likely to cause diseases with a
minimum time of 10 s. Whilst this may seem very energy intensive, it should be
noted that the energy is recovered and reused with heat exchangers. Availability
of a cheap energy source is of greater importance for practical application.
2. UV radiation. UV radiation is electromagnetic radiation with a wavelength
between 200 and 400 nm. Wavelengths between 200 and 280 nm (UV-C), with
an optimum at 254 nm, has a strong killing effect on micro-organisms, because it
minimizes the multiplication of DNA chains. Different levels of radiation are
needed for different organisms so as to achieve the same level of efficacy. Runia
(1995) recommends a dose which varies from 100 mJ cm2 for eliminating
bacteria and fungi to 250 mJ cm2 for eliminating viruses. These relatively
high doses are needed to compensate for variations in water turbidity and
variations in penetration of the energy into the solution due to low turbulence
around the UV lamp or variations in output from the UV lamp. Zoschke et al.
(2014) reviewed that UV irradiation at 185 and 254 nm offers water organic
4 Hydroponic Technologies 105
1. Ozone (O3). Ozone is produced from dry air and electricity using an ozone-
generator (converting 3O2 ! 2O3). The ozone-enriched air is injected into the
water that is being sanitized and stored for a period of 1 h. Runia (1995)
concluded that an ozone supply of 10 g per hour per m3 drain water with an
exposure time of 1 h is sufficient to eliminate all pathogens, including viruses.
The reduction of microbial populations in vegetable production in soilless sys-
tems managed with ozone has also been observed by Nicoletto et al. (2017).
Human exposure to the ozone that vents from the system or the storage tanks
should be avoided since even a short exposure time of a concentration of
0.1 mg L1 of ozone may cause irritation of mucous membranes. A drawback
of the use of ozone is that it reacts with iron chelate, as UV does. Consequently,
higher dosages of iron are required and measures need to be taken to deal with
iron deposits in the system. Recent research (Van Os 2017) with contemporary
ozone installations looks promising, where complete elimination of pathogens
and breakdown of remaining pesticides is achieved, with no safety problems.
2. Hydrogen peroxide (H2O2). Hydrogen peroxide is a strong, unstable oxidizing
agent that reacts to form H2O and an O- radical. Commercially so-called activa-
tors are added to the solution to stabilize the original solution and to increase
efficacy. Activators are mostly formic acid or acetic acid, which decrease pH in
the nutrient solution. Different dosages are recommended (Runia 1995) against
Pythium spp. (0.005%), other fungi (0.01%), such as Fusarium, and viruses
(0.05%). The 0.05% concentration is also harmful to plant roots. Hydrogen
peroxide is especially helpful for cleaning the watering system, whilst the use
for disinfection has been taken over by other methods. The method is considered
inexpensive, but not efficient.
106 C. Maucieri et al.
Disinfection methods are not very selective between pathogens and other organic
material in the solution. Therefore, pretreatment (rapid sand filters, or 50–80 um
mechanical filters) of the solution before disinfection is recommended at heat
treatment, UV radiation and ozone treatment. If after disinfection residuals of the
chemical methods remain in the water, they may react with the biofilms which have
been formed in the pipe lines of the watering systems. If the biofilm is released from
the walls of the pipes, they will be transported to the drippers and cause clogging.
Several oxidizing methods (sodium hypochlorite, hydrogen peroxide with activa-
tors, chlorine dioxide) are mainly used to clean pipe lines and equipment, and these
create a special risk for clogging drippers over time.
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Part II
Specific Aquaponics Technology
Chapter 5
Aquaponics: The Basics
W. Lennard (*)
Aquaponic Solutions, Blackrock, VIC, Australia
e-mail: willennard@gmail.com
S. Goddek
Mathematical and Statistical Methods (Biometris), Wageningen University, Wageningen,
The Netherlands
e-mail: simon.goddek@wur.nl; simon@goddek.nl
5.1 Introduction
advantages may have been supplied via the eutrophic or semi-eutrophic lake sedi-
ments rather than directly from any designed or actively integrated fish production
system (Morehart 2016; Baquedano 1993).
Modern aquaponics started in the USA in the 1970s and was co-evolved by
several institutions with an interest in more sustainable farming practices. Early
important work was performed by several researchers, but ultimately, the progenitor
of nearly all modern aquaponics is thought to be the work performed by, and the
systems produced by, James Rakocy and his team at the University of the Virgin
Islands (UVI) starting in the early 1980s (Lennard 2017).
Aquaponics is now considered a new and emerging industry with a relevant place
in the broader, global agricultural production context and there are a number of
variations of the technology of integrating fish culture with aquatic plant culture that
are collectively defined under the aquaponics banner or name (Knaus and Palm
2017). Therefore, aquaponics seeks to integrate aquaculture animal production with
hydroponic plant production using various methods to share water and nutrient
resources between the major production components to produce commercial and
saleable fish and plant products.
P S
N
Mg
K Ca
Fig. 5.1 Schematic representation of the nutrient flows within an aquaponic system. Fish feed is
the major nutrient entry point. The fish eat the feed, use what nutrients they need, release the rest as
waste and this waste is then partitioned between the microbes, plants and system water. (adapted
from Lennard 2017)
2017), some concentrate on approaches that do not return the water from the plants
to the fish (Delaide et al. 2016) and others include both recirculating and decoupled
methods (Knaus and Palm 2017). Further still, some researchers are including the
use of aquaculture effluents irrigated to soil-based crop production under the
aquaponic title (Palm et al. 2018). Historically, aquaponics, as the breakdown of
the word (aquaculture and hydroponics) suggests, was defined as only concerning
aquaculture and hydroponic plant production (Rakocy and Hargreaves 1993), so
current attempts at associations with soil-based culture seem incongruous.
Whilst aquaponic systems do integrate tank-based aquaculture technologies with
hydroponic plant culture technologies, aquaponic systems work by supplying nutri-
ents to, and partitioning nutrients between, the production inhabitants (fish and
plants) and the inhabitants that perform biological and chemical services that assist
the production inhabitant outcome (microflora) (Fig. 5.1) (Lennard 2017). There-
fore, is aquaponics more a system associated with nutrient supply, dynamics and
partitioning rather than one associated with the technology, equipment or hardware
applied?
Over the past decades, the definition of aquaponics has included a similar theme,
with subtle variations. The broadest definition has generally been provided in the
scientific publications of Rakocy and his UVI team, for example:
Aquaponics is the combined culture of fish and plants in closed recirculating systems.
– Rakocy et al. (2004a, b)
This early definition was based on the assumption that one-loop, fully
recirculating systems, consisting of a recirculating aquaculture component and a
5 Aquaponics: The Basics 117
hydroponic component, represented all aquaponic systems, which at the time, they
did. Graber and Junge (2009) expanded the definition, due to changes and develop-
ments in the approach, as follows:
Aquaponic is a special form of recirculating aquaculture systems (RAS), namely a
polyculture consisting of fish tanks (aquaculture) and plants that are cultivated in the
same water circle (hydroponic).
– Graber and Junge (2009)
The definition issue, or clarifying “what can be defined as aquaponics”, has been
a point of discussion over the past years. One of the main areas of development has
been that of multi-loop (or decoupled) aquaponic systems that aim at providing
additional fertilisers to the plants in order to expose them to an optimal nutrient
concentration (Goddek 2017). There should be no opposition between the ideologies
of fully recirculating and multi-loop aquaponic methodologies, both have their
respective places and applications within the appropriate industrial context and a
single common driving force of both should be that the technology, whilst being
nutrient and water efficient, also needs to be economically competitive to establish
itself in the market. In order to replace conventional practices, more than an ideology
needs to be offered to potential clients/users – i.e. technical and economic feasibility.
The European COST sponsored Aquaponics Hub (COST FA1305 2017) applies
the definition “. . .a production system of aquatic organisms and plants where the
majority (> 50%) of nutrients sustaining the optimal plant growth derives from
waste originating from feeding the aquatic organisms”, which clearly places an
emphasis on the nutrient sharing aspect of the technology.
It must also be stated that the proportion of fish to plants should remain at a level
that supports a core prospect of aquaponics; that plants are grown using fish wastes.
A system containing one fish and several hectares of hydroponic plant cultivation,
for example, should not be considered as aquaponics, simply because that one fish
effectively contributes nothing to the nutrient requirements of the plants. Since the
labelling of aquaponic products plays an increasingly important role in consumer
choice, we want to encourage a discussion by redefining aquaponics based on these
multiple developments of the technology. Even though we advocate closing the
nutrient cycle to the highest possible degree in the context of best practicable means,
a potential definition should also take all developments into consideration.
118 W. Lennard and S. Goddek
Recirculating
Process Water
Fig. 5.2 Simplified scheme of the main water flows within a coupled aquaponic system. The
nutrient concentrations in the process water are equally distributed throughout the whole system
5 Aquaponics: The Basics 119
Process Water
(One-Way Flow)
Fig. 5.3 Simplified scheme of the main water flows within a decoupled aquaponic system. The
nutrient concentrations in each component may be separately tailored to the individual component
requirement
120 W. Lennard and S. Goddek
should provide the prescribed advantages, and if the technology does not provide the
advantages, then the word should not be applied (Lennard 2017).
Because aquaponics may be defined either in terms of its hardware equipment
integration aspect (RAS with hydroponics), its nutrient sharing or partitioning
properties or its ability to provide important advantages, there is still a wide spectrum
of possible applications of the name to many different technical approaches that
utilise different methods and demand different outcomes. Therefore, it appears that
the actual definition of aquaponics is still unresolved.
It appears therefore that very important questions are yet to be answered: what is
aquaponics and how is it defined?
This would suggest that one very important aspect for the aquaponic industry to
consider is the development of a truthful and agreed-upon definition. The broader
aquaponics industry will continue to be full of disagreement if a definition is not
agreed upon, and more importantly, consumers of the products produced within
aquaponic systems will become more and more confused about what aquaponics
actually is – a state of affairs that will not assist the growth and evolution of the
industry.
Even though the definition of aquaponics has not been entirely resolved, there are
some general principles that are associated with the broad range of aquaponic
methods and technologies.
Using the nutrients added to the aquaponic system as optimally and efficiently as
possible to produce the two main products of the enterprise (i.e. fish and plant
biomass) is an important and shared first principle associated with the technology
(Rakocy and Hargreaves 1993; Delaide et al. 2016; Knaus and Palm 2017). There is
no use in adding nutrients (which possess an inherent cost in terms of money, time
and value) to a system to watch a high percentage of those nutrients are partitioned
into processes, requirements or outcomes that are not directly associated with the fish
and plants produced, or any intermediary life forms that may assist nutrient access by
the fish and plants (i.e. microorganisms – bacteria, fungi, etc.) (Lennard 2017).
Therefore, probably the most important general principle associated with aquaponics
is to use the applied nutrients as efficiently as possible to achieve the optimised
production of both fish and plants.
This same argument may also be applied to the water requirement of the
aquaponic system in question; again, the water added to the system should be
utilised principally by the fish and plants and used as efficiently as possible and
not allowed to leak to processes, life forms or outcomes that are not directly
associated with fish and plant production or may impact on the surrounding envi-
ronment (Lennard 2017).
In real terms, the efficient use of nutrients and water leads to several design
principles that are broadly applied to the aquaponic method:
5 Aquaponics: The Basics 121
1. The most important principle of aquaponics is to use the wastes produced by the
fish as a principle nutrient source for the plants. In fact, this is the entire idea of
aquaponics and so should be a first order driver for the method. Aquaponics was
historically envisaged as a system to grow plants using fish aquaculture wastes so
that those aquaculture wastes had less environmental impact and were seen as a
positive and profitable commodity, rather than a troublesome waste product with
an associated cost to meet environmental legislative requirements (Rakocy and
Hargreaves 1993; Love et al. 2015a, b).
2. The system design should encourage the use of fish keeping and plant culturing
technologies that do not inherently uptake or destructively utilise the water or
nutrient resources added. For example, fish keeping components based on using
earthen ponds are discouraged, because the earthen pond has the ability to use
and make unavailable water and nutrient resources to the associated fish and
plants, thus lowering the water and nutrient use efficiency of the system.
Similarly, hydroponic plant culturing methods should not use media that
uptakes excessive amounts of nutrients or water and renders them unavailable
to the plants (Lennard 2017).
3. The system design should not waste nutrients or water via the production of
external waste streams. Principally, if water and nutrients leave the system via a
waste stream, then that water and those nutrients are not being used for fish or
plant production, and therefore, that water and those nutrients are being wasted,
and the system is not as efficient as possible. In addition, the production of a
waste streams can have a potential environmental impact. If waste water and
nutrients do leave the aquaponic system, they should be used in alternate,
exterior-to-system plant production technologies so water and nutrients are not
wasted, contribute to the overall production of edible or saleable biomass and do
not present a broader environmental impact potential (Tyson et al. 2011).
4. The system should be designed to lower or ideally, completely negate, direct
environmental impact from water or nutrients. A first order goal of aquaponics is
to use the wastes produced by the fish as a nutrient source for the plants so as to
negate the release of those nutrients directly to the surrounding environment
where they may cause impacts (Tyson et al. 2011).
5. Aquaponic system designs should ideally lend themselves to being located within
environmentally controlled structures and situations (e.g. greenhouses, fish
rooms). This allows the potential to achieve the best productive rates of fish
and plants from the system. Most aquaponic designs are relatively high in terms
of capital costs and ongoing costs of production, and therefore, the ability to
house the system in the perfect environment enhances profit potentials that
financially justify the high capital and costs of production (Lennard 2017).
The above outlined principles of design directly associate with a set of general
principles that are often, but not always, applied to the aquaponic production
environment. These general principles relate to how the system operates and how
nutrients are portioned among the system and its inhabitants.
122 W. Lennard and S. Goddek
The basic premise of aquaponics, in a nutrient dynamic context, is that fish are fed
fish feed, fish metabolise and utilise the nutrients in the fish feed, fish release wastes
based on the substances in the fish feed they do not utilise (including elements),
microflora access those fish metabolic wastes and use small amounts of them, but
transform the rest, and the plants then access and remove those microflora
transformed, fish metabolic wastes as nutrient sources and, to some extent, clean
the water medium of those wastes and counteract any associated accumulation
(Rakocy and Hargreaves 1993; Love et al. 2015a, b).
Because earthen-based fish production systems remove nutrients themselves,
aquaponics generally utilises what are known as recirculating aquaculture system
(RAS) principles for the fish production component (Rakocy and Hargreaves 1993;
Timmons et al. 2002). Fish are kept in tanks made of materials that do not remove
nutrients from the water (plastic, fibreglass, concrete, etc.), the water is filtered to
treat or remove the metabolic waste products of the fish (solids and dissolved
ammonia gases) and the water (and associated nutrients) is then directed to a plant
culturing component whereby the plants use the fish wastes as part of their nutrient
resource (Timmons et al. 2002). As for the fish, earthen-based plant culturing
components are not used because the soils involved remove nutrients and may not
necessarily make them fully available to the plants. In addition, hydroponic plant
culturing techniques do not use soil and are cleaner than soil-based systems and
allow some passive control of the microorganism mixtures present.
Plants cultured in conventional hydroponics require the addition of what are
known as mineral fertilisers: nutrients that are present in their basal, ionic forms
(e.g. nitrate, phosphate, potassium, calcium, etc. as ions) (Resh 2013). Conversely,
recirculating aquaculture systems must apply regular (daily) water exchanges to
control the accumulation of fish waste metabolites (Timmons et al. 2002).
Aquaponics seeks to combine the two separate enterprises to produce an outcome
that achieves the best of the two technologies while negating the worst (Goddek
et al. 2015).
Plants require a suite of macro and micro elements for optimal and efficient
growth. In aquaponics, the majority of these nutrients arise from the fish wastes
(Rakocy and Hargreaves 1993; Lennard 2017; COST FA1305 2017). However, fish
feeds (the major source of aquaponic system nutrients) do not contain all the
nutrients required for optimised plant growth, and therefore, external nutrition, to
varying extents, is required.
Standard hydroponics and substrate culture add nutrients to the water in forms
that are directly plant-available (i.e. ionic, inorganic forms produced via designed
salt variety additions) (Resh 2013). A proportion of the wastes released by fish are in
forms that are directly plant-available (e.g. ammonia) but potentially toxic to the fish
(Timmons et al. 2002). These dissolved, ionic fish waste metabolites, like ammonia,
are transformed by ubiquitous bacterial species that replace hydrogen ions with
oxygen ions, the product from ammonia being nitrate, which is far less toxic to the
fish and the preferred nitrogen source for the plants (Lennard 2017). Other nutrients
appropriate to plant uptake are bound in the solid fraction of the fish waste as organic
5 Aquaponics: The Basics 123
compounds and require further treatment via microbial interaction to render the
nutrients available to plant uptake (Goddek et al. 2015). Therefore, aquaponic
systems require a suite of microflora to be present to perform these transformations.
The key to optimised aquaponic integration is determining the ratio between fish
waste output (as directly influenced by fish feed addition) and plant nutrient
utilisation (Rakocy and Hargreaves 1993; Lennard and Leonard 2006; Goddek
et al. 2015). Various rules of thumb and models have been developed in an attempt
to define this balance. Rakocy et al. (2006) developed an approach that matches the
plant growing area requirement with the daily fish feed input and called it “The
Aquaponic Feeding Rate Ratio”. The feeding rate ratio is set between 60 and
100 grams of fish feed added per day, per square meter of plant growing area
(60–100 g/m2/day). This feeding rate ratio was developed using Tilapia spp. fish
eating a standard, 32% protein commercial diet (Rakocy and Hargreaves 1993). In
addition, the aquaponic system this ratio is particular to (known as the University of
the Virgin Islands Aquaponic System – UVI System) does not utilise the solid fish
waste fraction, is over-supplied with nitrogen and requires in-system, passive
de-nitrification to control the nitrogen accumulation rate (Lennard 2017). Others
have determined alternate ratios based on different fish and plant combinations,
tested in different specific conditions (e.g. Endut et al. 2010 – 15–42 g/m2/day for
African catfish, Clarias gariepinus and water spinach plants, Ipomoea aquatica).
The UVI feeding rate ratio was developed by Rakocy and his team as an
approximate approach; hence why it is stated as a range (Rakocy and Hargreaves
1993). The UVI ratio tries to account for the fact that different plants require
different nutrient amounts and mixtures and therefore a “generic” aquaponic design
approach is a difficult prospect. Lennard (2017) has developed an alternate approach
that seeks to directly match individual fish waste nutrient production rates (based on
the fish feed utilised and the fish conversion and utilisation of that feed) with specific
plant nutrient uptake rates so that exacting fish to plant ratio matching for any fish or
plant species chosen may be realised and accounted for in the aquaponic system
design. He matches this design approach with a specific management approach that
also utilises all the nutrients available within the fish solid waste fraction (via aerobic
remineralisation of the fish solid wastes) and only adds the nutrients required by the
chosen plant species for culture that are missing from the fish waste production
fractions. Therefore, this substantially lowers the associated feeding rate ratio
(e.g. less than 11 g/m2/day for some leafy green varieties as a UVI equivalent) and
allows any fish species to be specifically and exactly matched to any plant species
chosen (Lennard 2017). Similarly, Goddek et al. (2016) have proposed models that
allow more exacting fish to plant component ratio determination for decoupled
aquaponic systems.
The general principles of efficient nutrient use, low and efficient water use, low or
negated environmental impact, ability to be located away from traditional soil
resources and sustainability of resource use are the general principles applied to
aquaponic system design and configuration and their ongoing application should be
encouraged within the field and industry.
124 W. Lennard and S. Goddek
Water is the key medium used in aquaponic systems because it is shared between the
two major components of the system (fish and plant components), it is the major
carrier of the nutrient resources within the system and it sets the overall chemical
environment the fish and plants are cultured within. Therefore, it is a vital ingredient
that may have a substantial influence over the system.
In an aquaponic system, water-based environment context, the source of water
and what that source water contains chemically, physically and biologically are a
major influence over the system because it sets a baseline for what is required to be
added to the system by the various inputs of the system. These inputs, in turn, effect
and set the environment that the fish and plants are cultured within. For example,
some of the major inputs in terms of nutrients to any aquaponic system include, but
are not limited to, the fish feed (a primary nutrient resource for the system), the
buffers applied (which assist to control and set the pH values associated with both
the fish and plant components) and any external nutrient additions or supplementa-
tions required to meet the nutrient needs of the fish and plants (Lennard 2017).
Fish feeds are designed to provide the nutrition required for fish growth and
health and therefore contain nutrient mixtures and quantities primarily to aid the fish
being cultured (Timmons et al. 2002; Rakocy et al. 2006). Plants, on the other hand,
have different nutrient requirements to fish, and fish feeds rarely, if ever, meet the
total nutrient requirements of the plants (Rakocy et al. 2006). Because of this,
aquaponic systems that culture fish and plants solely using fish feed-derived nutrient
resources may efficiently and optimally produce fish, but they rarely do so for the
plants. The best aquaponic system designs recognise that the ultimate outcome is to
produce both fish and plants at optimal and efficient growth rates and therefore, also
recognise that some form of additional nutrition is required to meet the total plant
nutrient requirement (Rakocy et al. 2006; Suhl et al. 2016).
Classical, fully recirculating aquaponic systems generally rely on fish feeds
(after the fish have consumed that feed, metabolised it and utilised the nutrients
within it) as the major nutrient source for the plants and supplement any missing
nutrients required by the plants via some form of buffering regime (Rakocy et al.
2006) or via additional nutrient supplementation (e.g. adding chelated nutrient
forms directly to the culture water or by adding nutrients via foliar sprays) (Roosta
and Hamidpour 2011).
The best example of this classical recirculating aquaponic approach is the UVI
(University of the Virgin Islands) aquaponic system developed by Dr. James Rakocy
and his UVI team (Rakocy and Hargreaves 1993; Rakocy et al. 2006). The UVI
design principally adds nutrients for both fish and plant culture via fish feed
additions. However, fish feeds do not contain enough calcium (Ca+) and potassium
(K+) for optimal plant culture. The bacteria-mediated conversion of fish waste-
dissolved ammonia to nitrate causes system-wide production of hydrogen ions
within the water column, and the proliferation of these hydrogen ions results in a
constant fall in the system water pH towards acid. The buffering regime employed
5 Aquaponics: The Basics 125
adds the missing calcium and potassium by adding basic salts (often salts based on
carbonate, bicarbonate or hydroxyl ions paired with calcium or potassium) to the
system that assist to control the system water pH at a level that meets both the shared
pH environmental requirements of the fish and the plants, whilst providing the
additional calcium and potassium the plants require (Rakocy et al. 2006). In addi-
tion, the UVI system adds another major nutrient for plant growth that is not
available in standard fish feeds, iron (Fe), via regular and controlled iron chelate
additions. Therefore, the potassium, calcium and iron the plants require that are not
found in the fish feed are available via these two additional nutrient supply mech-
anisms (Rakocy et al. 2006).
Decoupled aquaponic designs adopt an approach to culture the fish and plants in a
way whereby the water is used by the fish and the fish waste nutrients are supplied to
the plants, without recirculation of the water back to the fish (Karimanzira et al.
2016). Decoupled designs therefore allow more flexibility in customising the water
chemistry, after fish use, for optimised plant production because supplementation of
the nutrients not present in the fish feed (and fish waste) may be achieved with no
concerns of the water returning to the fish (Goddek et al. 2016). This means
decoupled designs potentially may apply more exacting nutrient mixtures and
strengths to the culture water, post fish use, for plant culture, and this may be
achieved with more exacting and intense nutrient supplementation.
In both cases (recirculating and decoupled aquaponic system designs), an under-
standing of the chemical quality of the source water is vital so that as close to optimal
nutrient concentrations for the plants may be achieved. If, for example, the source
water contains calcium (a case often seen when ground water resources are utilised),
this will affect and change the buffering regime applied to recirculating aquaponic
designs and the extent of the nutrient supplementation applied to a decoupled design
because the calcium present in the source water will offset any required supplemen-
tation required for plant calcium needs (Lennard 2017). Or, if the source water
contains elevated sodium (Na+) concentrations (again, often seen with ground water
resources and a nutrient plants do not use and which can accumulate in system
waters), it is important to know how much is present so management methods may
be applied to avoid potential plant nutrient toxicity (Rakocy et al. 2006). The
chemical nature of the source water, therefore, is vital to overall aquaponic system
health and management.
Ultimately, because source water chemistry can affect aquaponic system nutrient
management and because aquaponic operators like to have the ability to manipulate
aquaponic water and nutrient chemistry to a high degree, a water source with little, if
any, associated water chemistry is highly desirable (Lennard 2017). In this sense,
rainwater or water treated for chemical removal (e.g. reverse osmosis) is the best
source water for aquaponics in a water chemistry context (Rakocy et al. 2004a, b;
Lennard 2017). Ground waters are also suitable, but it must be ensured that they do
not contain chemicals or salts in concentrations that are too high to be practical
(e.g. high magnesium or iron concentrations) or contain chemical species that are not
used by the fish or plants (e.g. high sodium concentrations) (Lennard 2017). River
waters may also be suitable as aquaponic source water, but as for other water
126 W. Lennard and S. Goddek
sources, they should be tested for chemical presence and concentrations. Town water
sources (i.e. water reticulated and supplied for domestic and consumptive purposes)
are broadly applied in aquaponics (Love et al. 2015a, b) and are also acceptable if
they contain acceptable nutrient, salt or chemical concentrations. In the case of town-
or municipal-supplied water resources, it should be noted that many supplies have
some form of sterilisation applied to make the water drinkable for humans. If this
source of water is to be used for aquaponics, then it is important to ensure that any
chemicals that may be applied to achieve sterilisation (e.g. chlorine, chloramine,
etc.) are not present in concentrations that could harm the fish, plants or microor-
ganisms within the aquaponic system (Lennard 2017).
The chemistry associated with source water is not the only factor that needs
consideration when supplying source water for aquaponic use. Many natural waters
may also contain microbial and other microorganisms that may affect the overall
ecological health of the aquaponic system or present a discernible human health risk.
Rainwaters rarely contain microbes themselves; however, the vessels or tanks the
rainwater may be stored within may contain or allow microbial proliferation. Ground
waters are usually good in terms of microbial presence but may also contain high
microbial loads, especially if sourced from areas associated with animal farming or
human waste treatment. River waters may also contain high microbial loads due to
farming or human waste treatment outflows and again should be checked via detailed
microbial analysis (Lennard 2017).
Because the chemical and microbial nature of the source water used in aquaponic
systems can have potential effects on system water chemistry and microbiology, it is
recommended that any applied water source be sterilised and treated for chemical
removal (e.g. reverse osmosis, distillation, etc.) before being used in an aquaponic
system (Lennard 2017). If sterilisation is universally applied, the chance of intro-
ducing any foreign and unwanted microbes to the system is substantially lowered. If
water treatment and filtration is applied, any chemicals, salts, unwanted nutrients,
pesticides, herbicides, etc. will be removed and therefore cannot contribute nega-
tively to the system.
A clean water source, free of microbes, salts, nutrients and other chemicals allows
the aquaponic operator to manipulate the system water to contain the nutrient
mixture and strength they require without the fear that any external influences may
affect the operation of the system or the health and strength of the fish and plants and
is a vital requirement for any commercial aquaponic operation.
Aquaponics represents an effort to control water quality so that all the present life
forms (fish, plants and microbes) are being cultured in as close to ideal water
chemistry conditions as possible (Goddek et al. 2015). If water chemistry can be
matched to the requirements of these three sets of important life forms, efficiency
and optimisation of growth and health of all may be aspired to (Lennard 2017).
5 Aquaponics: The Basics 127
Nitrogen
Phosphorus
Potassium
Sulfur
Calcium
Magnesium
Iron
Manganese
Boron
Molybdenum
Fig. 5.4 Example of a standard pH mediated, nutrient availability chart for aquatically cultured
plants. Red line represents a normal operating pH for a hydroponic system; the blue line that for an
aquaponic system
(Timmons et al. 2002; Goddek et al. 2015; Suhl et al. 2016). In natural freshwater
environments, most fish species require an environmental pH (i.e. water pH) that
closely matches the internal pH of the fish, which is often close to a pH of 7.4
(Lennard 2017). In addition, the major microbes associated with dissolved metabo-
lite transformation in RAS culture (the nitrification bacteria of several species) also
require a pH around 7.5 for optimal ammonia transformation to nitrate (Goddek et al.
2015; Suhl et al. 2016). Therefore, RAS operators apply a pH set point of approx-
imately 7.5 to RAS freshwater fish culture.
There is an obvious difference between a pH of 5.5 (an average for standard,
sterilised, hydroponic plant culture) and a pH of 7.5 (an average standard for RAS
fish culture). Therefore, it is argued broadly that pH represents one of the largest
water quality compromises present in aquaponic science (Goddek et al. 2015; Suhl
et al. 2016). Advocates of decoupled aquaponic designs often cite this difference in
optimal pH requirement as an argument for the decoupled design approach, stating
that fully recirculating designs must find a pH compromise when decoupled designs
5 Aquaponics: The Basics 129
have the luxury of applying different water pH set points to the fish and plant
components (Suhl et al. 2016; Goddek et al. 2016). However, what this argument
ignores is that aquaponic systems, as opposed to hydroponic systems, are not sterile
and employ ecological aquatic techniques that encourage a diverse population of
microflora to be present within the aquaponic system (Eck 2017; Lennard 2017).
This results in a broad variety of present microbes, many of which form intricate and
complex associations with the plants, especially the plant roots, within the aquaponic
system (Lennard 2017). It is well known and established in plant physiology that
many microbes, associated with the soil medium and matrix, closely associate with
plant roots and that many of these microbes assist plants to access and uptake vital
nutrients (Vimal et al. 2017). It is also known that some of these microbes produce
organic molecules that directly further assist plant growth, assist plant immunity
development and assist to outcompete plant (especially root) pathogens (Vimal et al.
2017; Srivastava et al. 2017). In essence, these microbes assist plants in many ways
that are simply not present in the sterilised environment applied in standard hydro-
ponic culture.
With these diverse microbes present, the plants gain access to nutrients in many
ways that are not possible in systems that rely on aquatic pH settings alone to enable
plant nutrient access (e.g. standard hydroponics and substrate culture). Many of
these microbes operate at broad pH levels, just like other soil-based microbes, such
as the nitrification bacteria (pH of 6.5–8.0, Timmons et al. 2002). Therefore, with
these microbes present in aquaponic systems, the pH set point may be raised above
what is normally applied in hydroponic or substrate culture techniques (i.e. pH of
4.5–6.0) while advanced and efficient plant growth is still present (Lennard 2017).
This is evidenced in the work of several aquaponic researchers who have demon-
strated better plant growth rates in aquaponics than in standard hydroponics (Nichols
and Lennard 2010).
Other water quality requirements in aquaponic systems relate to physical/chem-
ical parameters and more specifically, plant nutrient requirement parameters. In
terms of physical/chemical requirements, plants, fish and microbes share many
commonalities. Dissolved oxygen (DO) is vital to fish, plant roots and microflora
and must be maintained in aquaponic systems (Rakocy and Hargreaves 1993;
Rakocy et al. 2006). Plant roots and microflora generally require relatively lower
DO concentrations than most fish; plant roots and microbes can survive with DO
below 3 mg/L (Goto et al. 1996), whereas most fish require above 5 mg/L (Timmons
et al. 2002). Therefore, if the DO concentration within the aquaponic system is set
and maintained for the fish requirement, the plant and microbe requirement is also
met (Lennard 2017). Different fish species require different DO concentrations:
warm water fish (e.g. Tilapia spp., barramundi) can generally tolerate lower DO
concentrations than cool water fish species (e.g. salmonids like rainbow trout and
arctic char); because the fish DO requirement is almost always greater than the plant
roots and microfloral requirement, DO should be set for the specific fish species
being cultured (Lennard 2017).
Water-carbon dioxide (CO2) concentrations, like that for DO, are generally set
by the fish because the plant roots and microbes can tolerate higher concentrations
130 W. Lennard and S. Goddek
than the fish. Carbon dioxide concentrations are important to optimal fish health
and growth and are often ignored in aquaponic designs. Parameters and set points
for CO2 concentrations should be the same as for the same fish species cultured in
fish-only, RAS systems and in general, should be kept below 20 mg/L (Masser
et al. 1992).
Water temperature is important to all the present life forms within an aquaponic
system. Fish and plant species should be matched as closely as possible for water
temperature requirements (e.g. Tilapia spp. of fish like 25 C plus, and plants like
basil thrive in this relatively high water temperature; lettuce varieties like cooler
water, and therefore, a better matched fish candidate is rainbow trout) (Lennard
2017). However, as for other water physical and chemistry parameters, meeting the
fish’s requirement for water temperature is paramount because the microbes have the
ability to undergo specific species selection based on the ambient conditions
(e.g. nitrification bacterial species differentiation occurs at different water tempera-
tures and the species that matches best to the particular water temperature will
dominate the nitrification bacterial biomass of the system) and many plants can
grow very well at a broader range of water temperatures (Lennard 2017). Matching
the water temperature, and maintaining it within plus or minus 2 C (i.e. a high-level
temperature control) to the fish, is an important requirement in aquaponics because
when water temperature is correct and does not deviate from the ideal average, the
fish achieve efficient and optimised metabolism and eat and convert feed efficiently,
leading to better fish growth rates and stable and predictable waste load releases,
which assists plant culture (Timmons et al. 2002).
Maintaining water clarity (low turbidity) is another important parameter in
aquaponic culture (Rakocy et al. 2006). Most water turbidity is due to suspended
solids loads that have not been adequately filtered, and these solids may affect fish by
adhering to their gills, which may lower potential oxygen transfer rates and ammonia
release rates (Timmons et al. 2002). Suspended solids loads less than 30 mg/L are
recommended for aquaponically cultured fish (Masser et al. 1992; Timmons et al.
2002). High suspended solids loads also affect plant roots because they have the
ability to adhere to the roots which may cause nutrient uptake inefficiency, but more
commonly provides increased potential for pathogenic organism colonisation, which
leads to poor root health and ultimate plant death (Rakocy et al. 2006). These
suspended solids also encourage the prevalence of heterotrophic bacteria (species
that break down and metabolise organic carbon) which, if allowed to dominate
systems, may outcompete other required species, such as nitrification bacteria.
Electrical conductivity (EC) is a measure often applied in hydroponics to gain an
understanding of the amount of total nutrient present in the water. It, however,
cannot provide information on the nutrient mix, the presence or absence of individ-
ual nutrient species or the amount of individual nutrient species present (Resh 2013).
It is not often applied in aquaponics because it only measures the presence of ionic
(charged) nutrient forms, and it has been argued that aquaponics is an organic
nutrient supply method, and therefore, EC is not a relevant measure (Hallam
2017). However, plants generally only source ionic forms of nutrients, and therefore,
5 Aquaponics: The Basics 131
nutrient testing of the water should be employed so that nutrient mixture and strength
may be maintained and managed as a very important water quality requirement.
The major input to any aquaponic system are the nutrients added because aquaponic
systems are designed to efficiently partition the nutrients added to them to the three
important forms of life present: the fish and plants (which are the main products of
the system) and the microflora (which assist to make the added nutrients available to
the fish and plants) (Lennard 2017).
In classical, fully recirculating aquaponic designs, one of the key design drivers is
to use the main nutrient input source, the fish feed, as efficiently as possible and
therefore fully recirculating designs strive to supply as many of the nutrients required
for the plants from the fish feed (Lennard 2017). Decoupled designs, on the other
hand, place an emphasis on optimised plant growth by directly comparing the
nutrient mixtures and strengths applied in standard hydroponics and substrate culture
and trying to replicate those within the aquaponic context and therefore do not strive
to supply as many of the nutrients required for the plants from the fish feed and
utilise substantial external nutrient supplementations to achieve the required plant
growth rates (Delaide et al. 2016). This means that a different emphasis is placed on
the origin of the nutrients added, based on the technical design approach, and this,
therefore, affects the main nutrient supply source of the aquaponic system; for fully
recirculating designs, the major plant nutrient source is fish feed (via fish waste
production), and for decoupled designs the major nutrient supply source for the
plants is external supplements (e.g. nutrient salts) (Lennard 2017).
Fully recirculating aquaponic designs, such as the UVI aquaponic system model,
rely on the fish feed as the major nutrient source for the system (Rakocy et al. 2006).
The fish feed is added to the fish, which eat it, metabolise it and use the nutrients
134 W. Lennard and S. Goddek
from it as required and then produce a waste stream (both solids and dissolved). This
waste stream from the fish becomes the major nutrient source for the plants, and
hence, the fish feed is the major nutrient source for the plants. The UVI system
provides approximately 80% or more of the nutrients required to grow the plants
from the fish feed alone (Lennard 2017). The remaining nutrients required for plant
growth, because the fish feed does not contain them in the amounts required, are
added via a nutrient supplementation method that provides the dual role of
supplementing the additional nutrients and controlling the system aquatic pH
(Rakocy et al. 2006). This dual role approach is referred to as “buffering” and the
supplement is referred to as “buffer”. For the UVI model, the two important plant
nutrients identified as lacking in fish feed and which require supplementation are
potassium (K) and calcium (Ca) and are supplemented daily via the buffering
regime. In addition, plant-required iron (Fe) is also lacking in the fish feed and is
supplemented in a chelated form via direct addition to the system water at a
frequency measured in weeks (i.e. every 2–4 weeks based on weekly aquatic iron
analysis) (Rakocy et al. 2006).
Other fully recirculating aquaponic design approaches or methods place an even
higher emphasis on providing nutrients via the fish feed. Lennard (2017) has
developed a method for fully recirculating systems that supplies greater than 90%
of the nutrients required for plant growth from the fish feed added. The increase in
the efficiency of nutrients supplied via the fish feed of this method when compared to
the UVI method is that this approach remineralises the solid fish wastes (via external,
bacteria-mediated biodigestion) and adds these nutrients back into the aquaponic
system for plant utilisation, whereas the UVI method sends the majority of the solid
fish wastes to an external waste stream (Rakocy et al. 2006; Lennard 2017). This
approach also adds nutrients deficient in the fish feed for plant growth via a buffering
regime; however, this regime is far more exacting and allows greater manipulation of
nutrient strengths and mixtures than the UVI approach (Lennard 2017).
Therefore, the major nutrient addition pathways for most fully recirculating
aquaponic system designs are the fish feed (major route), buffer external supple-
mentation for added potassium and calcium (minor route) and direct supplementa-
tion of iron chelate (minor route).
Decoupled aquaponic system designs, such as those being widely adopted cur-
rently in Europe, rely on a mixture of fish feed nutrients and active, external
supplementation to provide the nutrients required for plant growth (Suhl et al.
2016). Because decoupled designs do not return water from the plant component
to the fish component, it is possible to customise the nutrient profile within the water
specifically to the plant requirement (Goddek et al. 2016). Therefore, decoupled
aquaponic designs almost always rely on substantial external nutrient supplementa-
tion to meet the plant requirement and place far less emphasis on providing as much
nutrition as possible for the plants from the fish wastes. In addition, the amount of
external supplementation is substantial when compared to fully recirculating
approaches (Lennard 2017) with external fractions regularly 50% or more of the
total plant nutrient requirement or greater (Goddek 2017). The external nutrients
5 Aquaponics: The Basics 135
Aquaponics, until recently, has been dominated by fully recirculating (or coupled)
design approaches that share and recirculate the water resource constantly between
the two major components (fish and plant culture) (Rakocy et al. 2006; Lennard
2017). In addition, the low to medium technology approaches historically applied to
aquaponics have driven a desire to remove costly components so as to increase the
potential of a positive economic outcome. One of the filtration components almost
always applied to standard RAS and hydroponics/substrate culture technologies, that
of aquatic sterilisation, has regularly not been included by aquaponic designers.
Sterilisation in a RAS and hydroponic/substrate culture context is universally
applied because the high densities of either the fish or plants cultured usually
136 W. Lennard and S. Goddek
attract pressure from aquatic, pathogenic organisms that substantially lower overall
production rates (Van Os 1999; Timmons et al. 2002). The major reason for this
increased aquatic pest pressure in both technologies is that each concentrates on
providing minimal biotic, ecological resources and therefore allows considerable
“ecological space” within the system water for biotic colonisation. In these “open”
biological conditions, pest and pathogenic species proliferate and tend to colonise
quickly to take advantage of the species present (i.e. fish and plants) (Lennard
2017). In this context, sterilisation or disinfection of the culture water has histor-
ically be seen as an engineered approach to counteract the issue (Van Os 1999;
Timmons et al. 2002). This means that both RAS and hydroponic/substrate culture
industries adopt a sterilisation approach to control pathogenic organisms within the
associated culture water.
Aquaponics has always placed an emphasis on the importance of the associated
microbiology to perform important biological services. In all the coupled aquaponic
designs of Rakocy and his UVI team, a biological filter was not included because
they demonstrated that the raft culture, hydroponic component provided more than
enough surface area to support the nitrifying bacteria colony size to treat all the
ammonia produced by the fish as a dissolved waste product and convert it to nitrate
(Rakocy et al. 2006, 2011). Rakocy and his team therefore did not advocate applied
sterilisation of the system water because it may have affected the nitrifying bacterial
colonies. This historical UVI/Rakocy perspective dictated aquaponic system design
into the future. Other advantages of not including aquatic sterilisation to aquaponic
systems were identified and discussed, especially in the context of assistive plant
microbiota (Savidov 2005; Goddek et al. 2016).
The current thinking in aquaponic research and industry is that not applying any
form of aquatic sterilisation or disinfection allows the system water to develop a
complex aquatic ecology that consists of many different microbiological life forms
(Goddek et al. 2016; Lennard 2017). This produces a situation similar to a natural
ecosystem whereby a high diversity of microflora interacts with each other and the
other associated life forms within the system (i.e. fish and plants). The proposed
outcome is that this diversity leads to a situation in which no single pathogenic
organism can dominate due to the presence of all of the other microflora and can
therefore not cause devastating effects to fish or plant production. It has been
demonstrated that aquaponic systems contain a high diversity of microflora (Eck
2017) and via the proposed ecological diversity mechanism outlined above, assis-
tance to both fish and plant health and growth is provided via this microbial diversity
(Lennard 2017).
The non-sterilised, ecologically diverse approach to aquaponics has been historically
applied to coupled or fully recirculating aquaponic designs (Rakocy et al. 2006),
whereas a sterilised, hydroponic analogy has been proposed for some decoupled
aquaponic design approaches (Monsees et al. 2016; Priva 2009; Goddek 2017).
However, it appears more decoupled designers are now applying principles that take
an ecological, non-sterilised approach into consideration (Goddek et al. 2016; Suhl
et al. 2016; Karimanzira et al. 2016) and therefore acknowledge there is a positive effect
associated with a diverse aquaponic microflora (Goddek et al. 2016; Lennard 2017).
5 Aquaponics: The Basics 137
Because there are two separate, existing, analogous technologies that produce fish
and plants at high rates (RAS fish culture and hydroponic/substrate culture plant
production), a reason for their integration seems pertinent. RAS produces fish at
productive rates in terms of individual biomass gain, for the feed weight added, that
rivals, if not betters, other aquaculture methods (Lennard 2017). In addition, the high
fish densities that RAS allows lead to higher collective biomass gains (Rakocy et al.
2006; Lennard 2017). Hydroponics and substrate culture possess, within a controlled
environment context, advanced production rates of plants that better most other
agriculture and horticulture methods (Resh 2013). Therefore, initially, there is a
requirement for aquaponics to produce fish and plants at rates that equal these two
separate productive technologies; if not, then any loss of productive effort counts
against any integration argument. If the productive rate of the fish and plants in an
aquaponic system can equal, or better, the RAS and hydroponic industries, then a
further case may be made for other advantages that may occur due to the integration
process.
Standard hydroponics or substrate culture has been directly compared with
aquaponics in terms of the plant growth rates of the two technologies. Lennard
(2005) compared aquaponic system lettuce production to a hydroponic control in
several replicated laboratory experiments. He demonstrated that aquaponic lettuce
production was statistically lower in aquaponics (4.10 kg/m2) when compared to
hydroponics (6.52 kg/m2) when a standard approach to media bed aquaponic system
design and management was applied. However, he then performed a series of
experiments that isolated specific parameters of the design (e.g. reciprocal vs
constant hydroponic subunit water delivery, applied water flow rate to the hydro-
ponic subunit and comparing different hydroponic subunits) or comparing specific
management drivers (e.g. buffering methodologies and species and the overall
starting nutrient concentrations) to achieve optimisation and then demonstrated
that aquaponics (5.77 kg/m2) was statistically identical to hydroponic lettuce pro-
duction (5.46 kg/m2) after optimisation of the aquaponic system based on the
improvements suggested by his earlier experiments, the result suggesting that
improvements to coupled or fully recirculating aquaponic designs can equal standard
hydroponic plant production rates. Lennard (2005) also demonstrated fish survival,
SGR, FCR and growth rates equal to those exhibited in standard RAS and extensive
pond aquaculture for the fish species tested (Australian Murray Cod).
Pantanella et al. (2010) also demonstrated statistically similar lettuce production
results within high fish density (5.7 kg/m2 lettuce production) and low fish density
(5.6 kg/m2 lettuce production) aquaponic systems compared to a standard hydro-
ponic control (6.0 kg/m2).
Lennard (Nichols and Lennard 2010) demonstrated statistically equal or better
results for all lettuce varieties and almost all herb variety production tested in a
nutrient film technique (NFT) aquaponic system when compared to a hydroponic
NFT system within the same greenhouse.
138 W. Lennard and S. Goddek
fact, it has been proposed that water may even be recovered from that lost due to
plant evapotranspiration via employing some form of air water content harvesting
scheme or technology (Kalantari et al. 2017). Coupled aquaponic systems appear to
provide a greater potential to conserve and lower water use (Lennard 2017). If the
nutrient dynamics between fish production and plant use can be balanced, the only
water loss is via plant evapotranspiration, and because the water is integrally shared
between the fish and plant components, daily makeup water volumes simply repre-
sent all the water lost from the system plants (Lennard 2017). Decoupled aquaponic
designs present a more difficult proposition because the two components are not
integrally linked and the daily water use of the fish component does not match the
daily water use of the plant component (Goddek et al. 2016; Goddek and Keesman
2018). Therefore, water use and replacement rates for aquaponic systems are not
completely resolved and probably never will be due to the broad differences in
system design approaches.
Efficient nutrient utilisation is assigned to the aquaponic method and cited as an
advantage of the aquaponic approach (Rakocy et al. 2006; Blidariu and Grozea
2011; Suhl et al. 2016; Goddek et al. 2015). This is generally because standard RAS
aquaculture utilises the nutrients within the fish feed to grow the fish, with the
remainder being sent to waste. Fish metabolise much of the feed they are fed, but
only utilise approximately 25–35% of the nutrients added (Timmons et al. 2002;
Lennard 2017). This means up to 75% of the nutrients added to fish-only RAS are
wasted and not utilised. Aquaponics seeks to use the nutrients wasted in RAS for
plant production, and therefore, aquaponics is said to use the nutrients added more
efficiently because two crops are produced from the one input source (Rakocy and
Hargreaves 1993; Timmons et al. 2002; Rakocy et al. 2006; Lennard 2017). The
extent of fish waste nutrient use does differ between the various aquaponic methods.
The fully recirculating UVI model does not utilise the majority of the solid fish
wastes generated in the fish component and sends them to waste (Rakocy et al.
2006), the fully recirculating Lennard model takes this a step further by using all the
wastes generated by the fish component (dissolved wastes directly and solids via
external microbial remineralisation with main system replacement) (Lennard 2017).
Many decoupled approaches also attempt to utilise all the wastes generated by the
fish component, via direct use of dissolved wastes and again, via external microbial
remineralisation with main system replacement (Goddek et al. 2016; Goddek and
Keesman 2018). All of these methods and approaches demonstrate that a primary
driver for the aquaponic method is to utilise as many of the added nutrients as
possible and therefore attempt to use the added nutrients as efficiently as possible.
Independence from soil has been cited as an advantage of the aquaponic method
(Blidariu and Grozea 2011; Love et al. 2015a, b). The advantage perceived is that
because soil is not required, the aquaponic system or facility may be located where
the operator chooses, rather than where suitable soil is present (Love et al. 2015a, b).
Therefore, the aquaponic method is independent of location based on soil availabil-
ity, which is an advantage over soil-based agriculture.
140 W. Lennard and S. Goddek
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Open Access This chapter is licensed under the terms of the Creative Commons Attribution 4.0
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Chapter 6
Bacterial Relationships in Aquaponics: New
Research Directions
Abstract The growth rates and welfare of fish and the quality of plant production in
aquaponics system rely on the composition and health of the system’s microbiota.
The overall productivity depends on technical specifications for water quality and its
movement amongst components of the system, including a wide range of parameters
including factors such as pH and flow rates which ensure that microbial components
can act effectively in nitrification and remineralization processes. In this chapter, we
explore current research examining the role of microbial communities in three units
of an aquaponics system: (1) the recirculating aquaculture system (RAS) for fish
production which includes biofiltration systems for denitrification; (2) the hydro-
ponics units for plant production; and (3) biofilters and bioreactors, including sludge
digester systems (SDS) involved in microbial decomposition and recovery/
remineralization of solid wastes. In the various sub-disciplines related to each of
these components, there is existing literature about microbial communities and their
importance within each system (e.g. recirculating aquaculture systems (RAS),
hydroponics, biofilters and digesters), but there is currently limited work examining
interactions between these components in aquaponics system, thus making it
an important area for further research.
A. Joyce (*)
Department of Marine Science, University of Gothenburg, Gothenburg, Sweden
e-mail: alyssa.joyce@gu.se
M. Timmons
Biological & Environmental Engineering, Cornell University, Ithaca, NY, USA
e-mail: mbt3@cornell.edu
S. Goddek
Mathematical and Statistical Methods (Biometris), Wageningen University, Wageningen,
The Netherlands
e-mail: simon.goddek@wur.nl; simon@goddek.nl
T. Pentz
Eat & Shine VOF, Velp, The Netherlands
e-mail: timea.pentz@eatandshine.nl
6.1 Introduction
address this aspect in more detail in the latter half of this review whilst referring the
reader to Chap. 3 for more details on solid separation techniques and Chaps. 7 and
8 for discussions on coupled vs decoupled aquaponics system. If we consider here
only dissolved and suspended particulates in the water (and not sludge), all
aquaponics system employ a range of different biofilters that expose the attached
microorganisms to organic matter passing through the filter and provide an appro-
priate substrate and sufficient surface area for microbial attachment and formation of
biofilms. Degradation of this organic matter provides energy to the microbial
communities, which in turn release macronutrients (e.g. nitrate, orthophosphate)
and micronutrients (e.g. iron, zinc, copper) back to the system in usable forms
(Blancheton et al. 2013; Schreier et al. 2010; Vilbergsson et al. 2016a).
There is considerable agricultural research on the role of microbiota in plant
rooting, growth and health. The preponderance of this research focuses on soil-based
systems; however, research on hydroponics has also increased in recent years
(Bartelme et al. 2018). The microbiota in aquaculture have also been similarly
well-characterized, where the role of microbes in fish health and digestion has
received considerable attention as researchers attempt to better characterize the
role of gut health on nutrient assimilation. Given the importance of biofiltration in
RAS systems, bacteria involved in the nitrification process for RAS have also been
comparatively well-studied and thus are not be addressed here (see Chaps. 10 and
12). However, there has been comparatively limited research on microbes in
aquaponics system, especially the crucial interactions of microbiota amongst various
compartments of the system. This lack of research currently limits the scope and
productivity of such systems, where there is considerable potential for enhancement
with pre- and probiotics, as well as other opportunities to improve the health of
aquaponics system through a better understanding, and thus better ability to control,
the vast set of uncharacterized microbiota that affect system health and performance.
As such, this chapter focuses primarily on recent studies that reveal how and
where microbial communities determine productivity within compartments, whilst
also highlighting the relatively small number of studies linking those microbial
communities to interactions amongst components and overall system productivity.
We attempt to identify gaps where further knowledge about microbial communities
could address operational challenges and provide important insights for enhancing
efficiency and reliability.
New technologies for studying how microbial communities change over time, and
which groups of organisms predominate under particular environmental conditions,
have increasingly offered opportunities to anticipate adverse outcomes within sys-
tem components and thus lead to the design of better sensors and tests for the
effective monitoring of microbial communities in fish or plant cultures. For instance,
various ‘omics’ technologies – metagenomics, metatranscriptomics, community
148 A. Joyce et al.
Metabolomics characterizes the functions of genes, but the techniques are not
organism-specific or sequence-dependent and thus can reveal the wide range of
metabolites that are end-products of cellular biochemistry in organisms, tissues,
cells or cell compartment (depending on which samples are analysed). Nevertheless,
knowledge about the metabolome of microbial communities under particular envi-
ronmental conditions (microcosms) reveals a great deal about the biogeochemical
cycling of nutrients and the effects of perturbations. Such knowledge characterizes
various metabolic pathways and the range of metabolites present in samples. Sub-
sequent biochemical and statistical analyses can point to physiological states that can
in turn be correlated with environmental parameters which may not be evident from
genomic or proteomic approaches. Nevertheless, combining metabolomics with
gene function studies has tremendous potential in furthering aquaponics research;
see review (van Dam and Bouwmeester 2016).
Good food safety and ensuring animal welfare are high priorities in gaining public
support for aquaponics. One of the most frequent issues raised by food safety experts
in relation to aquaponics is the potential risk of contamination with human pathogens
when using fish effluent as fertilizer for plants (Chalmers 2004; Schmautz et al.
2017). A recent literature search to determine zoonotic risks in aquaponics con-
cluded that pathogens in contaminated intake water, or pathogens in components of
feeds originating with warm-blooded animals, can become associated with fish gut
microbiota, which, even if not detrimental to the fish themselves, can potentially be
passed up the food chain to humans (Antaki and Jay-Russell 2015). The mechanisms
of introduction of pathogens to an aquaponics system are thus of concern, with the
likeliest source of faecal coliforms or other pathogenic bacteria stemming from feed
inputs to fish. From a biological perspective, there are potential risks of these
pathogens proliferating either in biofilters, or, in one-loop systems by introducing
airborne pathogens from open plant components back to the fish tanks. Although
biosecurity risks are low in the relatively closed environmental space of an
aquaponics system – as compared for instance to open pond aquaculture – and are
even lower in decoupled aquaponics system wherein portions of the system can be
isolated, there is still a perception that fish sludge could be potentially dangerous
when applied to plants for human consumption. Escherichia coli (E. coli) is a human
enteric pathogen causing foodborne illnesses that has been a key concern regarding
the use of animal waste as fertilizer in agriculture or aquaculture, e.g. integrated
pig-fish systems (Dang and Dalsgaard 2012). However, it is generally not considered
to present a risk in fish-plant aquaponics. For instance, Moriarty et al. (2018)
150 A. Joyce et al.
instance, Sirakov et al. demonstrated that a Pseudomonas sp. that they isolated was
effective as a biocontrol for the pathogenic fungi Saprolegnia parasitica of fish and
Pythium ultimum of plants. The researchers also reported in vitro inhibition of a
variety of other bacterial isolates from the different aquaponics compartments, but
without testing their in vivo effects. The potential for using such isolates as biolog-
ical controls is not new, but applications of NGS techniques can now reveal more
about interactions of such isolates with each other and with potential pathogens, thus
making it possible to optimize the effectiveness of delivery. Use of other ‘omics’
techniques could help reveal overall community structure and associated metabolic
functions, and begin elucidating which organisms and functions are most beneficial.
In future, such techniques might allow selection for ‘helper strains’ within microbial
communities, or the identification of exudates that have anti-microbial effects
(Massart et al. 2015).
instance, improved performance in RAS systems has been noted when the pre-intake
filter is supplied with pulverized fish food to develop microbial communities more
similar to those in the rearing tanks (Attramadal et al. 2014).
The parameters for operating aquaponics at a given scale – including water volume,
temperature, feed and flow rates, pH, fish and crop ages and densities – all affect
the temporal and spatial distribution of the microbial communities that develop
within its compartments, for reviews: RAS (Blancheton et al. 2013); hydroponics
(Lee and Lee 2015).
In addition to controlling dissolved oxygen, carbon dioxide levels and pH in
aquaponics, it is also essential to control the accumulation of solids in the RAS
system as fine suspended particles can adhere to gills, cause abrasion and respiratory
distress and increase susceptibility to disease (Yildiz et al. 2017). More relevant, the
particulate organic matter (POM) must be quickly and effectively removed from
RAS systems, or else excessive heterotrophic growth will cause almost all unit
processes to fail. RAS feeding rates must be carefully managed to minimize solids
loading on the system (e.g. avoid over-feeding and minimize feeding costs). The
biophysical properties of feed – particle size, nutrient content, digestibility, sensory
appeal, density and settling rate – determine ingestion and assimilation rates, which
in turn have an impact on solids build-up and thus water quality. Although water
quality is frequently studied in the context of nutrient cycling (see Chap. 9), it is also
important to obtain a better understanding of the composition of microbial commu-
nities and changes in these based on feed composition, particulate loading and how
this influences the growth of heterotrophic and autotrophic bacterial communities.
Various features of RAS system designs have been developed specifically to deal
with solids (Timmons and Ebeling 2013); see also review: (Vilbergsson et al.
2016b). For instance, some biofilters function to keep substantial portions of wastes
suspended in order to facilitate degradation, whilst others mechanically filter through
screens or granular media. Still others rely on sedimentation to simply collect and
156 A. Joyce et al.
remove sludge. However, such methods are not particularly effective at recovering
nutrients within the sludge and making it bioavailable for plant use. Historically, this
sludge has been handled in bioreactors for its methanogenic value or dewatered to
be used as fertilizer for soil-based crops, but various newer designs have attempted to
improve recovery for use in the hydroponic component. Improving recovery of this
sludge is an important area of investigation given that a significant portion of the
essential macro- and micronutrients required for plant growth are bound to the
particulate organic matter, which, if discarded, is lost from the system. By adding
an additional sludge recycling loop to aquaponics system, solid wastes can be
converted into dissolved nutrients for reuse by plants rather than being discarded
(Goddek et al. 2018). Digesters or remineralizing bioreactors are one way of
accomplishing this, however one of the key areas that is currently under-developed
includes knowledge of how microbial communities within these sludge digesters can
be enhanced (e.g. through addition of microbes) or better utilized (e.g. through
better engineered design of linked reactors) to recover nutrients into bioavailable
forms for plants. Even though the actual microbial communities within sludge
digesters have not been well researched for aquaponics, there is considerable
literature on the microbiota of sludge digesters for sewage and animal wastes in
agriculture, including fish effluent, that can provide further insight into ideal designs
for sludge recovery in aquaponics system. Current research on the incorporation of
sludge into aquaponics system involves remineralization in digesters situated
between the RAS and hydroponic unit (Goddek et al. 2016a, 2018). Within aerobic
or anaerobic bioreactors, environmental conditions that are favourable for waste
degradation can effectively break down this sludge into bioavailable nutrients, which
can subsequently be delivered to hydroponics system without the presence of soil
(Monsees et al. 2017). Many one-loop aquaponics system already include aerobic
(Rakocy et al. 2004) and anaerobic (Yogev et al. 2016) digesters to transform
nutrients that are trapped in the fish sludge and make them bioavailable for plants.
The ability to decouple these has a number of advantages that are further discussed in
Chap. 8 and appears to lead to higher growth rates (Goddek and Vermeulen 2018).
However, despite the many advances, the actual technology to accomplish this
remains challenging. For example, some heterotrophic denitrifying bacteria cultured
in anoxic or even aerobic conditions with sludge from RAS will use nitrate as an
electron receptor and oxidized carbon sources for energy, while storing excess P as
polyphosphate along with divalent metal ions such as Ca+2 or Cu+2. When stressed at
alkaline pH, these bacteria degrade polyphosphate and release orthophosphate,
which is the necessary form for assimilation of phosphate by plants (Van Rijn
et al. 2006). Inserting remineralization bioreactor units, such as those in Goddek
et al. (2018), could provide a way to better recover P for hydroponics. Similar
methods have, for instance, been used with trout sludge from a RAS that were
treated for nitrate and P content in excess of allowable disposal limits (Goddek et al.
2015). However, the microbial communities involved in these processes are sensi-
tive to culture conditions such as C:N ratios, oxygenation, metal ions and pH, so
nitrites and other noxious intermediates can accumulate. Despite a vast literature on
digesters of various organic wastes, primarily anaerobic for biogas production
(Ibrahim et al. 2016), there is far less research on treating RAS wastes (Van Rijn
6 Bacterial Relationships in Aquaponics: New Research Directions 157
2013), and in the case of aquaponics system, even less available research about the
relationship between nutrient bioavailability and crop growth in hydroponics system
(Möller and Müller 2012). At this time, more studies of RAS sludge bioreactors
could provide important insights into culture conditions for microbial populations
that produce favourable results, for instance, on P recovery, and its introduction into
hydroponics units.
One of the current challenges in efforts to assess the recovery of P from sludge
arises when comparing trials of anaerobic and aerobic digesters for their efficacy
(Goddek et al. 2016b; Monsees et al. 2017). Although both studies used similar
sludge composition initially, the results were quite different. In one study (Monsees
et al. 2017), measures of various soluble nutrients in aerobic treatments resulted in a
330% increase in P concentration and a 16% decrease in nitrate concentration
compared to minor increases in P and a 97% decrease in nitrate in anaerobic
treatments. By contrast, results from a similar study (Goddek et al. 2016b) showed
that growth of lettuce plants in a hydroponic unit was superior using anaerobic
supernatant, even though both anaerobic and aerobic treatments only resulted in
slightly better nitrate recovery from anaerobic conditions and almost complete loss
of PO4 from both treatments (Goddek et al. 2016b). Obviously, factors such as feed
composition and rates, the suspension versus settling of solids, pH (maintained at
7 1 with CaOH2 in the former and variable 8.2–8.65 in the latter), sampling and
fish strains differed in these two studies. Nevertheless, the contrasting results for PO4
and NO3 indicate the need for further research to optimize nutrient recovery, with the
addition of a metagenomics approach to characterize microbial communities so as to
better understand their role in these processes.
6.7 Conclusions
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Chapter 7
Coupled Aquaponics Systems
coupled aquaponics to be installed in all geographic regions, from the high latitudes
to arid and desert regions, with specific adaptation to the local environmental
conditions. This chapter provides an overview of the historical development, general
system design, upscaling, saline and brackish water systems, fish and plant choices
as well as management issues of coupled aquaponics especially in Europe.
Keywords Coupled aquaponics · Fish and plant choice · Nutrient cycles · Polyponic
systems · Functions
7.1 Introduction
The combination of fish and plant cultivation in coupled aquaponics dates back to
the first design by Naegel (1977) in Germany, using a 2000 L hobby scale system
(Fig. 7.1) located in a controlled environment greenhouse. This system was devel-
oped in order to verify the use of nutrients from fish waste water under fully
controlled water recirculating conditions intended for plant production including a
dual sludge system (aerobic/anaerobic wastewater treatment). Naegel based his
concept on the open pond aquaponic system of the South Carolina Agricultural
Experiment Station, in the USA, where excess nutrients from the fishponds, stocked
with channel catfish (Ictalurus punctatus), were eliminated by the hydroponic
production of water chestnuts (Eleocharis dulcis) (Loyacano and Grosvenor
1973). By including nitrification and denitrification tanks to increase the nitrate
concentration inside his system, Naegel (1977) attempted a complete oxidation of
all nitrogenous compounds, reaching nitrate concentrations of 1200 mg/L, and
demonstrating the effectiveness of the nitrification step. Although the system was
stocked at a low density (20 kg/m3 each) using tilapia (Tilapia mossambica) and carp
(Cyprinus carpio), the tomatoes (Lycopersicon esculentum) and iceberg lettuce
(Lactuca scariola) grew well and produced harvestable yield. These first research
results led to the concept of coupled aquaponic systems, in which the plants
eliminate the waste produced by the fish, creating adequate growth, demonstrating
highly efficient water use in both units. The principle of coupled aquaponics was first
described by Huy Tran at the World Aquaculture Conference in 2015 (Tran 2015).
Coupled aquaponic systems do not necessarily use mechanical particulate filter-
ing in the classical sense and keep consistent nutrient flow between the aquaculture
and hydroponic units. The main challenge is how to manage the faecal load in the
coupled aquaponic system where the plants absorb the nutrients and particulate
waste can be removed from the system by filter presses or geotextiles.
The development of modern agriculture, human population growth and shrinking
resources worldwide, has promoted the development of coupled aquaponic systems.
Since fish farming is considerably more efficient in protein production and water use
compared with other farmed animals and since closed systems are largely site-
independent, coupled aquaponic systems have been able to develop worldwide
(Graber and Junge 2009), under arid conditions (Kotzen and Appelbaum 2010;
7 Coupled Aquaponics Systems 165
Fishes Plants
Nitrification
Air
Denitrification Sedimentation
Air
Return Sludge
Excess Sludge
Fig. 7.1 Diagram of the first system by Naegel (1977) growing tilapia and common carp in
combination with lettuce and tomatoes in a closed recirculation system
Appelbaum and Kotzen 2016) and even in urban settings (König et al. 2016). Most
described systems belong to domestic, small-scale and semi-commercial installa-
tions (Palm et al. 2018) that are driven by hobby aquarists, enthusiasts or smaller
start-up companies. New research results, summarized in this chapter, demonstrate
both the potentials and constraints regarding the continued development of these
systems into commercial aquaponics, being capable of making a significant contri-
bution to future food production.
Most original research efforts on coupled aquaponic systems took place in the USA
with an increasing presence in the EU partly initiated by COST Action FA1305, The
EU Aquaponics Hub and in other European research centres. Nowadays, fully
166 H. W. Palm et al.
The coupled aquaponics principle combines three classes of organisms: (1) aquatic
organisms, (2) bacteria and (3) plants that benefit from each other in a closed
recirculated water body. The water serves as a medium of nutrient transport, mainly
from dissolved fish waste, which is converted into nutrients for plant growth by
bacteria. These bacteria (e.g. Nitrosomonas spec., Nitrobacter spec.) oxidize ammo-
nium to nitrite and finally to nitrate. Therefore, it is necessary for the bacteria to
receive substantial amounts of ammonium and nitrite to stabilize colony growth and
the quantity of nitrate production. Consequently, in a coupled aquaponic system,
volumes are critically important, i) the aquaculture unit following the principles of
recirculating aquaculture systems (RAS), ii) the bacterial growth substrate and iii)
the space for the plant units and the amount of plants to be cultivated. Together, they
form the aquaponics unit (Fig. 7.2).
The specific biological-chemical components of the process water have particular
importance for coupled aquaponic systems. With food or uneaten feed particles, the
organic fish waste and the bacteria inside the process water, an emulsion of nutrients
combined with enzymes and digestive bacteria support the growth of fish and plants.
There is evidence that compared to stand-alone systems such as aquaculture (fish)
and hydroponics (plants), the growth of aquatic organisms and crops in a coupled
aquaponics can be similar or even higher. Rakocy (1989) described a slightly higher
Optional:
Feed Coupled Full Water Partial
Fertilization
Recirculation
Fishes Plants
168 H. W. Palm et al.
yield of tilapia (Tilapia nilotica, 46.8 kg) in coupled aquaponics in contrast to stand-
alone fish culture (41.6 kg) and slight increases in Summer Bibb lettuce yield
(385.1 kg) compared to vegetable hydroponic production (380.1 kg). Knaus et al.
(2018b) recorded that aquaponics increased biomass growth of O. basilicum, appar-
ently due to increased leaf generation of the plants (3550 leaves in aquaponics)
compared to conventional hydroponics (2393 leaves). Delaide et al. (2016) demon-
strated that aquaponic and hydroponic treatments of lettuce exhibited similar plant
growth, whereas the shoot weight of the complemented aquaponic solution with
nutrients performed best. Similar observations have been made by Goddek and
Vermeulen (2018). Lehmonen and Sireeni (2017) observed an increased root weight,
leaf area and leaf colour in Batavia salad (Lactuca sativa var. capitata) and iceberg
lettuce (L. sativa) with aquaponics process water from C. gariepinus combined with
additional fertilizer. Certain plants such as lettuce (Lactuca sativa), cucumbers
(Cucumis sativus) or tomatoes (Solanum lycopersicum) can consume nutrients
faster, and as a result flower earlier in aquaponics compared with hydroponics
(Savidov 2005). Also, Saha et al. (2016) reported a higher plant biomass yield in
O. basilicum in combination with crayfish Procambarus spp. and a low start-up
fertilization of the aquaponic system.
The basic system design of coupled aquaponics consists of one or more fish tanks,
a sedimentation unit or clarifier, substrates for the growth of bacteria or suitable
biofilters and a hydroponic unit for plant growth (Fig. 7.3). These units are connected
by pipes to form a closed water cycle. Often, after the mechanical filtration and the
biofilter, a pump sump is used (one pump or one loop system) which, as the deepest
point of the system, pumps the water back to the fish tanks from where it flows by
gravity to the hydroponic unit.
Sump
Fig. 7.3 Basic technical system design of a coupled aquaponic system with fish tank, sedimenter,
biofilter, hydroponic unit and a sump where the water is pumped or airlifted back to the fish tanks
and flows by gravity along the components
7 Coupled Aquaponics Systems 169
Coupled aquaponic systems are used in different scales. The closed-loop princi-
ple can be used in domestic systems (mini/hobby/backyard-coupled), demonstration
units (e.g. living walls coupled), commercial aquaponics and aquaponics farming
(with soil) ranging from small/semi-commercial to large-scale systems (Palm et al.
2018). A recent development in aquaponics has included partial fertilization, which
is dependent on the tolerance of the fish species. This, however, can result in a short-
term nutrient peak in the system but can be compensated through the nutrient
retention by the plants. In coupled aquaponics, an optimal ratio of the production
area (or fish volumes) of the aquaculture unit with the resulting feed demand as well
as an adequate amount of plants to be cultured in the hydroponic unit (plant
production area) must be achieved. (For discussions on the role of evapotranspira-
tion and solar radiation within the systems, see Chaps. 8 and 11). For gravel
aquaponics, Rakocy (2012) as a first attempt suggested ‘component ratio principles’,
with a fish-rearing volume of 1 m3 of fish tank volume to 2 m3 hydroponic media of
3 to 6 cm pea gravel as a rule of thumb. Ultimately, the amount of fish determines the
yield of crops in coupled aquaponics. Additionally, the technical conditions of the
fish-rearing unit must be adapted according to the needs of the cultivated aquatic
species.
The fish-rearing tanks (size, numbers and design) are selected depending on the scale
of production and fish species in use. Rakocy et al. (2006) used four large fish-
rearing tanks for the commercial production of O. niloticus in the UVI aquaponic
system (USA). With the production of omnivorous or piscivorous fish species, such
as C. gariepinus, several tanks should be used due to the sorting of the size classes
and staggered production (Palm et al. 2016). Fish tanks should be designed so that
the solids that settle at the bottom of the tanks can effectively be removed through an
effluent at the bottom. This solid waste removal is the first crucial water treatment
step in coupled aquaponics as is the case in aquaculture and decoupled aquaponics.
The waste originates from uneaten feed, fish faeces, bacterial biomass and floccu-
lants produced during aquaculture production, increasing BOD and reducing water
quality and oxygen availability with respect to both the aquaculture and hydroponic
units. In aquaculture, the solid waste consists to a large extent of organic carbon,
which is used by heterotrophic bacteria to produce energy through oxygen con-
sumption. The better the solid waste removal, the better the general performance of
the system for both fish and plants, i.e. with optimal oxygenation levels and no
accumulation of particles in the rhizosphere inhibiting nutrient uptake, and with
round or oval tanks proving to be particularly efficient (Knaus et al. 2015).
Fish production in coupled aquaponics in the FishGlassHouse in Germany was
tested at different scales in order to ascertain cost effectiveness. This was done
effectively as extensive (max. 50 kg, 35 fish m3) or intensive (max. 200 kg, 140 fish
m3) African catfish production. The semi-intensive production (max. 100 kg,
70 fish m3) cannot be recommended due to a negative cost benefit balance. In the
170 H. W. Palm et al.
semi-intensive production mode, system maintenance, labour and feed input were as
much as under intensive production but with reduced fish and plant biomass output,
and any economic gains in the aquaculture unit did not pay off (Palm et al. 2017).
This resulted from the high biochemical oxygen demands (BOD), high denitrifica-
tion because of the reduced oxygen availability, relatively high water exchange rates,
predominantly anaerobic mineralization with distinct precipitation, low P and
K-levels as well as a low pH-values with much less fish output compared with the
intensive conditions. In contrast, the extensive fish production allowed higher
oxygen availability with less water exchange rates and better nutrient availability
for plant growth. Thus, under the above conditions, a RAS fish production unit for
coupled aquaponics therefore either functions under extensive or intensive fish
production conditions, and intermediate conditions should be avoided.
7.4.1 Filtration
Clarifiers, sometimes also called sedimenters or swirl separators (also see Chap. 3),
are the most frequently used devices for the removal of solid waste in coupled
aquaponics (Rakocy et al. 2006; Nelson and Pade 2007; Danaher et al. 2013,
Fig. 7.4). Larger particulate matters must be removed from the system to avoid
anoxic zones with denitrifying effects or the development of H2S. Most clarifiers use
lamella or plate inserts to assist in solids removal. Conical bottoms support sludge
concentration at the bottom during operation and cleaning, whereas flat bottoms
require large quantities of water to flush out and remove the sludge. During opera-
tion, the solids sink to the bottom of the clarifier to form sludge. Depending on the
feed input and retention time, this sludge can build up to form relatively thick layers.
The microbial activity inside the sludge layers gradually shifts towards anaerobic
conditions, stimulating microbial denitrification. This process reduces plant avail-
able nitrate and should be avoided, especially if the process water is to be used for
hydroponic plant production. Consequently, denitrification can be counterproduc-
tive in coupled aquaponics.
The density of the solid waste removed by the clarifier is rather low, compared
with other technologies, maintenance is time-consuming, and cleaning the clarifier
with freshwater is responsible for the main water loss of the entire system. The
required amount of water is affected by its general design, the bottom shape and the
accessibility of the PVC baffles to flushing water (Fig. 7.4a, b). Increasing fish
stocking densities require higher quantities of water exchange (every day in the week
under intensive conditions) to maintain optimal water quality for fish production,
which can result in the loss of large amounts of process water, also losing substantial
amounts of nutrients required for plant growth. Furthermore, replacement with
freshwater introduces calcium and magnesium carbonates which may then precipi-
tate with phosphates. Therefore, the use of such manually operated clarifiers makes
predictions on process water composition with respect to optimal plant growth
nearly impossible (Palm et al. 2019). It would be more effective to follow
7 Coupled Aquaponics Systems 171
A
Partition Panel
PVC Baffles
Water Water
Inflow Dissolved Waste Outflow
Sludge
B C
Fig. 7.4 Principle of aquaponic filtration with a sedimenter (a–b) and (c) disc-filter
(PAL-Aquakultur GmbH, Abtshagen, Germany) of commercial African catfish (Clarias
gariepinus) RAS in the FishGlassHouse (Rostock University, Germany)
Naegle’s (1977) example of separating aerobic and anaerobic sludge and gaseous
nitrogen discharge with a dual sludge system.
More effective solid waste removal can be achieved by automatic drum- or disk-
filters which provide mechanical barriers that hold back solids, which are then
removed through rinsing. New developments aim to reduce the use of rinse water
through vacuum cleaning technologies, allowing the concentration of total solids in
the sludge up to 18% (Dr. Günther Scheibe, PAL-Aquakultur GmbH, Germany,
personal communication, Fig. 7.4c). Such effective waste removal has a positive
influence on the sludge composition, improving effluent water control in order to
better meet the horticultural requirements. Another option is the application of
multiple clarifiers (sedimenters) or sludge-removal components in a row.
Biofilters are another essential part of RAS, as they convert ammonia nitrogen via
microbial oxidation to nitrate (nitrification). Even though plant roots and the system
itself provide surfaces for nitrifying bacteria, the capability to control the water
quality is limited. Systems that do not have biofiltration are restricted to mini or
hobby installations with low feed inputs. As soon as the biomass of fish and the feed
input increases, additional biofilter capacity is required to maintain adequate water
quality for fish culture and to provide sufficient nitrate quantities for plant growth.
172 H. W. Palm et al.
For domestic and small-scale aquaponics, plant media (gravel or expanded clay for
example) can suffice as effective biofilters. However, due to the high potential for
clogging and thus the requirement for regular manual cleaning and maintenance,
these methods are not suitable for larger-scale commercial aquaponics (Palm et al.
2018). Additionally, Knaus and Palm (2017a) demonstrated that the use of a simple
biofilter in a bypass already increased the possible daily feed input in a backyard-
coupled aquaponic system by approximately 25%. Modern biofilters that are used in
intensive RAS are effective in providing sufficient nitrification capacity for fish and
plant production. Because of increased investment costs, such components are more
applicable in medium- and larger-scale commercial aquaponic systems.
In coupled aquaponics, a wide range of hydroponic subsystems can be used (also see
Chap. 4) depending on the scale of operation (Palm et al. 2018). Unless labour has no
significant impact on the yield (or profit) and the system is not too large, different
hydroponic subsystems can be used at the same time. This is common in domestic
and demonstration aquaponics that often use media bed substrate systems (sand,
gravel, perlite, etc.) in ebb and flow troughs, DWC channels (deep water culture or
raft systems) and even often self-made nutrient film channels (NFT). Most labour-
intensive are media substrate beds (sand/gravel) in ebb and flow troughs, which can
clog due to the deposition of detritus and often need to be washed (Rakocy et al.
2006). Due to the handling of the substrates, these systems are usually limited in
size. On the other hand, DWC hydroponic subsystems require less labour and are
less prone to maintenance, allowing them to be adopted for larger planting areas. For
this reason, DWC subsystems are mainly found in domestic to small/semi-
commercial systems, however, not usually in large-scale aquaponic systems. For
larger commercial aquaponic production, the proportion of labour and maintenance
in the DWC system is still seen to be too high. Even the use of water resources and
energy for pumping are also unfavourable for large-scale systems.
If closed aquaponic systems are designed for profit-oriented production, the use
of labour must decrease whilst the production area must increase. This is only
possible by streamlining fish production combined with the application of easy-to-
use hydroponic subsystems. The nutrient film technique (NFT) can, at present, be
considered the most efficient hydroponic system, combining low labour with large
plant cultivation areas and a good ratio of water, energy and investment costs.
However, not all aquaponic plants grow well in NFT systems and thus it is necessary
to find the right plant choice for each hydroponic subsystem, which in turn correlates
with the nutrient supply of a specific fish species integrated in a specific hydroponic
subsystem design. For coupled aquaponics, the sometimes higher particle load in the
water can be problematic by clogging drips, pipes and valves in NFT installations.
Hence, large aquaponic systems have to contain professional water management
with effective mechanical filtration to avoid recirculation blockages. When the
continuous supply of water is ensured through the pipes, the NFT system can be
7 Coupled Aquaponics Systems 173
used in all types of coupled aquaponic systems, but is most recommended for
production under small/semi-commercial systems and large-scale systems (Palm
et al. 2018).
Typical coupled aquaponic system range from small to medium scale and larger
sized systems (Palm et al. 2018). Upscaling remains one of the future challenges
because it requires careful testing of the possible fish and plant combinations.
Optimal unit sizes can be repeated to form multiunit systems, independent of the
scale of production. According to Palm et al. (2018), the range of aquaponic systems
were categorized into (1) mini, (2) hobby, (3) domestic and backyard, (4) small/
semi-commercial and (5) large(r)-scale systems, as described below:
Mini installations (Fig. 7.5) usually consist of a small fish reservoir such as a fish
tank or aquarium on which the plants grow on the surface or within a small
hydroponic bed. Conventional aquarium filters, aeration and pumps are usually
used. Mini systems are usually 2 m2 or less in size (Palm et al. 2018). These small
aquaponic systems can be used in the home with only few plants for home con-
sumption and planted with plants such as tomatoes, herbs or ornamentals. Such
systems add new values to human living space by adding ‘nature’ back into the
family life area which is especially popular in big cities. Some mini systems consist
of only a plant vase and one or more fish without filter and pump. However, these
systems are only short-term to operate because a regulated filtration is missing.
Hobby aquaponic systems are categorized to reach a maximum size of 10 m2
(Palm et al. 2018). With a higher fish stocking density, more feed and aeration, a
mechanical sedimentation unit (sedimenter/clarifier) is necessary (Fig. 7.6). The
sedimenter removes particulate matter –‘sludge’ such as faeces and uneaten feed
A
B
174 H. W. Palm et al.
from the system without using energy. The water flows by gravity from the fish tank
to the sedimenter and then through the hydroponic tanks and then drops into a sump
from where a pump or air lift pumps the water back to the fish tanks. In hobby
installations, the plant beds act as a natural microbial filter and often media bed
substrates such as sand, fine gravel or perlite are used. Hobby aquaponic systems are
more the category of gimmicks that do not target food production. They rather enjoy
the functionality of the integrated system. Hobby systems, as the name implies, are
usually installed by hobbyists who are interested in growing a variety of aquatic
organisms and plants for their own use and for ‘fun’.
Domestic/backyard aquaponics has the purpose of external home use production
of fish and plants characterized as having a maximum production area of 50 m2
(Palm et al. 2018). These systems are built by enthusiasts. The construction is
technically differentiated with a higher fish production, additional aeration and a
higher feed input. The coupled aquaponics principle is applied with the use of one
single pump which recirculates the water from a sump (lowest point) to higher
standing fish tanks and then by gravity via sedimenter and a biofilter (with aeration
and bacteria substrates) to the hydroponic units (Fig. 7.7).
For biofiltration, conventional bed filters can also be used as described in Palm
et al. (2014a, b, 2015). In backyard aquaponics, hydroponics could consist alone or
together of raft or DWC (deep water culture) troughs, substrate subsystems such as
coarse gravel/sand ebb and flow boxes or nutrient film technique (NFT) channels. In
the northern hemisphere, in outside installations, production is limited to the spring,
summer and early autumn periods because of the weather conditions. With this scale
of operation, fish and plants can be produced for private consumption (and produc-
tion can be extended through small greenhouse production), but direct sales in small
quantities are also possible.
Small and semi-commercial scale aquaponic systems are characterized by being
up to 100 m2 (Palm et al. 2018) with production focused on the retail market. More
tanks, often with a higher stocking density, additional filters and water treatment
7 Coupled Aquaponics Systems 175
A B C D E F
Fig. 7.7 Principle of a coupled domestic backyard aquaponic system, 10–50 m2 (from Palm et al.
2018) with (a) fish tank and aeration, (b) sedimenter or clarifier altered after Nelson and Pade
(2007), (c) biofilter with substrates and aeration, (d) hydroponic unit which could consists of
combined raft or DWC channels, (e) gravel or sand media substrate system, (f) nutrient film
technique NFT-channels and (g) a sump with one pump
systems and a larger hydroponic area with more diverse designs characterize these
systems.
Large(r)-scale commercial operations above 100 m2 (Palm et al. 2018) and
reaching many thousands of square metres reach the highest complexity and require
careful planning of the water flow and treatment systems (Fig. 7.8). General com-
ponents are multiple fish tanks, designed as intensive recirculation aquaculture
systems (RAS), a water transfer point or a sump allowing water exchange between
the fish and plants, and commercial plant production units (aquaponics s.s./s.l.). As
fish production is meant for intensive stocking densities, components such as
additional filtration with the help of drum filters, oxygen supply, UV light treatments
for microbial control, automatic controlled feeding and computerization including
automatic water quality control classify these systems.
These systems have a multiunit design capable of upscaling under fully closed
water recirculation which also allows for staggered production, parallel cultivation
of different plants that require different hydroponic subsystems and better control of
the different units in the case of disease outbreak and plant pest control.
F8 F5 F2
A
F9 F6 F3
S T Su
Wt-I Wt-II
Nu
Fig. 7.8 Schema (supervision) of a large-scale aquaponics module adopted after the
FishGlassHouse at University of Rostock (Germany) (1000 m2 total production area, Palm et al.
2018) with (a) independent aquaculture unit, (b) the water transfer system and (c) the independent
hydroponic unit; F1-F9 fish tanks, S) sedimenter, P-I pump one (biofilter pump), P-II pump two
(aquaculture recirculation pump), T) trickling filter, Su) sump. In the middle, nutrient water transfer
system with Wt-I) water transfer tank from the aquaculture unit, P-III) pump three, which pumps the
nutrient rich water from aquaculture to C) hydroponics unit on the right with Nu) nutrient tank and
an independent hydroponic recirculation system and planting tables (or NFT); P-IV) pump four,
which pumps the nutrient low water from the hydroponic unit back to Wt-II) water transfer tank two
and to the aquaculture unit for coupled (or decoupled if not used) aquaponic conditions
7 Coupled Aquaponics Systems 177
underground brackish water resources, and more than half the world’s underground
water is saline. Whilst the amount of underground saline water is only estimated as
0.93% of world’s total water resources at 12,870,000 km3, this is more than the
underground freshwater reserves (10,530,000 km3), which makes up 30.1% of all
freshwater reserves (USGS).
The first published research on the use of brackish water in aquaponics was carried
out in 2008–2009 in the Negev Desert of Israel (Kotzen and Appelbaum 2010). The
authors studied the potential for brackish water aquaponics that could utilize the
estimated 200–300 billion m3 located 550–1000 metres underground in the region.
This and additional studies used up to 4708–6800 μS/cm (4000–8000 μS/cm ¼ mod-
erately saline, Kotzen and Appelbaum 2010; Appelbaum and Kotzen 2016) in coupled
aquaponic systems with Tilapia sp. (red strain of Nile tilapia Oreochromis niloticus x
blue tilapia O. aureus hybrids), combined with deep water culture floating raft and
gravel systems. The systems were mirrored with potable water systems as a control. A
wide range of herbs and vegetables were grown, with very good and comparative
results in both brackish and freshwater systems. In both systems fish health and growth
were as good as plant growth of leeks (Allium ampeloprasum), celery (Apium
graveolens) (Fig. 7.9), kohlrabi (Brassica oleracea v. gongylodes), cabbage (Brassica
oleracea v. capitata), lettuce (Lactuca sativa), cauliflower (Brassica oleracea
v. botrytis), Swiss chard (Beta vulgaris vulgaris), spring onion (Allium fistulosum),
basil (Ocimum basilicum) and water cress (Nasturtium officinale) (Kotzen and
Appelbaum 2010; Appelbaum and Kotzen 2016).
A ‘mission report’ by van der Heijden et al. (2014) on integrating agriculture and
aquaculture with brackish water in Egypt suggests that red tilapia (probably red
strains of Oreochromis mossambicus) has high potential combined with vegetables
such as peas, tomatoes and garlic that can tolerate low to moderate salinity. Plants
that are known to have saline tolerance include the cabbage family (Brassicas), such
In larger scale commercial aquaponics fish and plant production need to meet market
demands. Fish production allows species variation, according to the respective
system design and local markets. Fish choice also depends on their impact onto
the system. Problematic coupled aquaponics fish production due to inadequate
nutrient concentrations, negatively affecting fish health, can be avoided. If coupled
aquaponic systems have balanced fish to plant ratios, toxic nutrients will be absorbed
by the plants that are cleaning the water. Since acceptance of toxic substances is
species dependent, fish species choice has a decisive influence on the economic
success. Therefore, it is important to find the right combination and ratio between the
fish and the plants, especially of those fish species with less water polluting activities
and plants with high nutrient retention capacity.
7 Coupled Aquaponics Systems 179
The benefits of having a particular fish family in coupled aquaponic systems are
not clearly understood with respect to their specific needs in terms of water quality
and acceptable nutrient loads. Naegel (1977) found there was no notable negative
impact on the fish and fish growth in his use of tilapia (Tilapia mossambica) and
common carp (Cyprinus carpio). The channel catfish (Ictalurus punctatus) was also
used by Lewis et al. (1978) and Sutton and Lewis (1982) in the USA. It was
demonstrated that the quality of the aquaponics water readily met the demands of
the different fish species, especially through the use of ‘easy-to-produce’ fish species
such as the blue tilapia (Oreochromis aureus, formerly Sarotherodon aurea) in
Watten and Busch (1984); Nile tilapia (Oreochromis niloticus), which was often
used in studies with different plant species as a model fish species (Rakocy 1989;
Rakocy et al. 2003, 2004; Al-Hafedh et al. 2008; Rakocy 2012; Villarroel et al.
2011; Simeonidou et al. 2012; Palm et al. 2014a, 2014b; Diem et al. 2017); and also
tilapia hybrids-red strain (Oreochromis niloticus x blue tilapia O. aureus hybrids),
that were investigated in arid desert environments (Kotzen and Appelbaum 2010;
Appelbaum and Kotzen 2016).
There has been an expansion in the types of fish species used in aquaponics, at
least in Europe, which is based on the use of indigenous fish species as well as those
that have a higher consumer acceptance. This includes African catfish (Clarias
gariepinus) which was grown successfully under coupled aquaponic conditions by
Palm et al. (2014b), Knaus and Palm (2017a) and Baßmann et al. (2017) in northern
Germany. The advantage of C. gariepinus is a higher acceptance of adverse water
parameters such as ammonium and nitrate, as well as there is no need for additional
oxygen supply due to their special air breathing physiology. Good growth rates of
C. gariepinus under coupled aquaponic conditions were further described in Italy by
Pantanella (2012) and in Malaysia by Endut et al. (2009). An expansion of African
catfish production under coupled aquaponics can be expected, due to unproblematic
production and management, high product quality and increasing market demand in
many parts of the world.
In Europe, other fish species with high market potential and economic value have
recently become the focus in aquaponic production, with particular emphasis on
piscivorous species such as the European pikeperch ‘zander’ (Sander lucioperca).
Pikeperch production, a fish species that is relatively sensitive to water parameters,
was tested in Romania in coupled aquaponics. Blidariu et al. (2013a, b) showed
significantly higher P2O5 (phosphorous pentoxide) and nitrate levels in lettuce
(Lactuca sativa) using pikeperch compared to the conventional production,
suggesting that the production of pikeperch in coupled aquaponics is possible
without negative effects on fish growth by nutrient toxicity. The Cyprinidae
(Cypriniformes) such as carp have been commonly used in coupled aquaponics
and have generally shown better growth with reduced stocking densities and min-
imal aquaponic process water flow rates (efficient water use) during experiments in
India. The optimal stocking density of koi carp (Cyprinus carpio var. koi) was at
1.4 kg/m (Hussain et al. 2014), and the best weight gain and yield of Beta vulgaris
var. bengalensis (spinach) was found with a water flow rate of 1.5 L/min (Hussain
et al. 2015). Good fish growth and plant yield of water spinach (Ipomoea aquatica)
with a maximum percentage of nutrient removal (NO3-N, PO4-P, and K) was
180 H. W. Palm et al.
reported at a minimum water flow rate of 0.8 L/min with polycultured koi carp
(Cyprinus carpio var. koi) and gold fish (Carassius auratus) by Nuwansi et al.
(2016). It is interesting to note that plant growth and nutrient removal in koi
(Cyprinus carpio var. koi) and gold fish (Carassius auratus) production (Hussain
et al. 2014, 2015) with Beta vulgaris var. bengalensis (spinach) and water spinach
(Ipomoea aquatica) increased linearly with a decrease in process water flow between
0.8 L/min and 1.5 L/min. These results suggest that for cyprinid fish culture, lower
water flow is recommended as this has no negative impacts on fish growth. In
contrast, however, Shete et al. (2016) described a higher flow rate of 500 L h1
(approx. 8 L/min) for common carp and mint (Mentha arvensis) production, indi-
cating the need for different water flow rates for different plant species. Another
cyprinid, the tench (Tinca tinca), was successfully tested by Lobillo et al. (2014) in
Spain and showed high fish survival rates (99.32%) at low stocking densities of
0.68 kg m3 without solids removal devices and good lettuce survival rates (98%).
Overall, members of the Cyprinidae family highly contribute to the worldwide
aquaculture production (FAO 2017); most likely this would also be true under
aquaponic conditions and productivity, but the economic situation should be tested
for each country separately.
Other aquatic organisms such as shrimp and crayfish have been introduced into
coupled aquaponic production. Mariscal-Lagarda et al. (2012) investigated the
influence of white shrimp process water (Litopenaeus vannamei) on the growth of
tomatoes (Lycopersicon esculentum) and found good yields in aquaponics with a
twofold water sparing effect under integrated production. Another study compared
the combined semi-intensive aquaponic production of freshwater prawns
(Macrobrachium rosenbergii – the Malaysian shrimp) with basil (Ocimum
basilicum) versus traditional hydroponic plant cultivation with a nutrient solution
(Ronzón-Ortega et al. 2012). However, basil production in aquaponics was initially
less effective (25% survival), but with increasing biomass of the prawns, the plant
biomass also increased so that the authors came to a positive conclusion with the
production of basil with M. rosenbergii. Sace and Fitzsimmons (2013) reported a
better plant growth in lettuce (Lactuca sativa), Chinese cabbage (Brassica rapa
pekinensis) and pakchoi (Brassica rapa) with M. rosenbergii in polyculture with the
Nile tilapia (O. niloticus). The cultivation with prawns stabilized the system in terms
of the chemical-physical parameters, which in turn improved plant growth, although
due to an increased pH, nutrient deficiencies occurred in the Chinese cabbage and
lettuce. In general, these studies demonstrate that shrimp production under
aquaponic conditions is possible and can even exert a stabilizing effect on the closed
loop – or coupled aquaponic principle.
The cultivation of many species of plants, herbs, fruiting crops and leafy vegetables
have been described in coupled aquaponics. In many cases, the nutrient content of
the aquaponics process water was sufficient for good plant growth. A review by
7 Coupled Aquaponics Systems 181
Fig. 7.10 Three quality categories of ivy (Hedera helix), grown in a coupled aquaponic system
indicating the quality that the nursery trade requires (a) very good and directly marketable, (b) good
and marketable and (c) not of high enough quality
7 Coupled Aquaponics Systems 183
Besides the chosen plant and variant, there are two major obstacles that concern
aquaponics plant production under the two suggested states of fish production,
extensive and intensive. Under extensive conditions, nutrient availability inside the
process water is much lower than under commercial plant production, nutrients such
as K, P and Fe are deficient, and the conductivity is between 1000 and 1500 μS / cm,
which is much less than applied under regular hydroponic production of commercial
plants regularly between 3000 and 4000 μS / cm. Plants that are deficient in some
nutrients can show signs of leaf necroses and have less chlorophyll compared with
optimally fertilized plants. Consequently, selective addition of some nutrients
increases plant quality that is required to produce competitive products.
In conclusion, commercial plant production of coupled aquaponics under inten-
sive fish production has the difficulty to compete with regular plant production and
commercial hydroponics at a large scale. The non-optimal and according to Palm
et al. (2019) unpredictable composition of nutrients caused by the fish production
process must compete against optimal nutrient conditions found in hydroponic
systems. There is no doubt that solutions need to be developed allowing optimal
plant growth whilst at the same time providing the water quality required for the fish.
Combining fish and plants in closed aquaponics can generate better plant growth
(Knaus et al. 2018b) combined with benefits for fish welfare (Baßmann et al. 2017).
Inside the process water, large variations in micronutrients and macronutrients may
occur with negative effects on plant nutritional needs (Palm et al. 2019). A general
analysis of coupled aquaponic systems has shown that there are low nutrient levels
within the systems (Bittsanszky et al. 2016) in comparison with hydroponic nutrient
solutions (Edaroyati et al. 2017). Plants do not tolerate an under or oversupply of
nutrients without effects on growth and quality, and the daily feed input of the
aquaponic system needs to be adjusted to the plant’s nutrient needs. This can be
achieved by regulating the stocking density of the fish as well as altering the fish
feed. Somerville et al. (2014) categorized plants in aquaponics according to their
nutrient requirements as follows:
1. Plants with low nutrient requirements (e.g. basil, Ocimum basilicum)
2. Plants with medium nutritional requirements (e.g. cauliflower, Brassica oleracea
var. Botrytis)
3. Plants with high nutrient requirements such as fruiting species (e.g. strawberries,
Fragaria spec.).
Not all plants can be cultured in all hydroponic subsystems with the same yield. The
plant choice depends on the hydroponic subsystem if conventional soilless aquaponic
systems (e.g. DWC, NFT, ebb and flow; aquaponics sensu stricto’ – s.s. – in the narrow
sense) are used. Under aquaponics farming (‘aquaponics sensu lato’ – s.l. – in a broader
sense, Palm et al. 2018), the use of inert soil or with addition of fertilizer applies gardening
techniques from horticulture, increasing the possible range of species.
184 H. W. Palm et al.
7.7.4 Polyponics
Fig. 7.11 Experiments with a variety of commonly grown vegetables, under winter conditions in
winter 2016/2017 in the FishGlassHouse (University of Rostock, Germany)
Table 7.1 Recommendation for the use of gardening plants in aquaponic farming with the use of
50% of the regular fertilizer in pots with soil
Name Lat. Name Possible for aquaponics Mark Nutrient regime
Beans Phaseolus vulgaris Yes 1 Extensive
Peas Pisum sativum No 2 Intensive
Beet Beta vulgaris No 2 Both
Tomatoes Solanum lycopersicum No 2.3 Both
Lamb’s lettuce Valerianella locusta Yes 1 Both
Radish Raphanus sativus Yes 1 Both
Wheat Triticum aestivum No 2 Both
Lettuce Lactuca sativa Yes 1 Intensive
Coupled aquaponics depends on the nutrients that are provided from the fish units,
either a commercial intensive RAS or tanks stocked under extensive conditions in
smaller operations. The fish density in the latter is often about 15–20 kg/m3 (tilapia,
carp), but extensive African catfish production can be higher up to 50 kg/m3. Such
different stocking densities have a significant influence on nutrient fluxes and
nutrient availability for the plants, the requirement of water quality control and
adjustment as well as appropriate management practices.
The process water quality with respect to nutrient concentrations is primarily
dependent on the composition of the feed and the respective turnover rates of the
fish. The difference between feed input and feed nutrients, assimilating inside the
fish or lost through maintenance of the system, equals the maximum potential of
7 Coupled Aquaponics Systems 187
Fig. 7.12 Unused nutrients in African catfish aquaculture that are potentially available for
aquaponic plant production (original data)
Nutrient Output
35 10
Macronutrient Output (%)
Fig. 7.13 Distribution of macro- and micronutrients inside the process water and the solids. (Data
from Strauch et al. (2018))
plant available nutrients from aquaculture. As noted above, the nutrient concentra-
tions should be adjusted to levels, which allow the plants to grow effectively.
However, not all fish species are able to withstand such conditions. Consequently,
resilient fish species such as the African catfish, tilapia or carp are preferred
aquaponic candidates. At the University of Rostock, whole catfish and its standard
diet as output and input values were analysed to identify the turnover rates of the
macronutrients N, P, K, Ca, Mg and S and the micronutrients Fe, Mn, Mo, Cu, Zn
and Se. With the exception of P, more than 50% of the feed nutrients given to the fish
are not retained in its body and can be considered potentially available as plant
nutrients (Strauch et al. 2018; Fig. 7.12). However, these nutrients are not equally
distributed inside the process water and the sediments. Especially macronutrients
(N, P, K) accumulate in the process water as well as inside the solid fraction whilst
the micronutrients, such as iron, disappear in the solid fraction separated by the
clarifier. Figure 7.13 shows the nutrient output per clarifier cleaning after 6 days of
188 H. W. Palm et al.
0,9
5
N-Budget / kg Feed -1 0,8
0,7 4
0,6
0,5 3
0,4
2
0,3
0,2 1
0,1
0 0
0 50 100 150
-1
Stocking Density (Fish Tank )
Fig. 7.14 N-budget per kg feed and oxygen level in African catfish aquaculture under three
different stocking densities (original data)
The following discussion reveals a number of key pros and challenges of coupled
aquaponics as follows:
Pro: Coupled aquaponic systems have many food production benefits, especially
saving resources under different production scales and over a wide range of
geographical regions. The main purpose of this production principle is the most
efficient and sustainable use of scarce resources such as feed, water, phosphorous
as a limited plant nutrient and energy. Whilst, aquaculture and hydroponics
(as stand-alone), in comparison to aquaponics are more competitive, coupled
aquaponics may have the edge in terms of sustainability and thus a justification of
these systems especially when seen in the context of, for example, climate
change, diminishing resources, scenarios that might change our vision of sustain-
able agriculture in future.
Pro: Small-scale and backyard-coupled aquaponics are meant to support local and
community-based food production by households and farmers. They are not able
to stem high investment costs and require simple and efficient technologies. This
applies for tested fish and plant combinations in coupled aquaponics.
Pro: The plants in contemporary coupled aquaponics have the similar role in treating
waste as constructed wetlands do in the removal of waste from water (Fig. 7.15).
The plants in the hydroponic unit in coupled aquaponics therefore fulfil the task
of purifying the water and can be considered a ‘biological advanced unit of water
purification’ in order to reduce the environmental impact of aquaculture.
Challenge: It has been widely accepted that using only fish feed as the input for plant
nutrition is often qualitatively and quantitatively insufficient in comparison to
conventional agriculture production systems (e.g. N-P-K hydroponics manure)
(Goddek et al. 2016), limiting the growth of certain crops in coupled aquaponics.
Pro: Coupled aquaponic systems have a positive influence on fish welfare. Most
recent studies demonstrate that in combination with cucumber and basil, the
agonistic behaviour of African catfish (C. gariepinus) was reduced (Baßmann
et al. 2017, 2018). More importantly, comparing injuries and behavioural patterns
with the control, aquaponics with high basil density influenced African catfish
even more positively. Plants release substances into the process water like
phosphatases (Tarafdar and Claassen 1988; Tarafdar et al. 2001) that are able to
hydrolyse biochemical phosphate compounds around the root area and exude
organic acids (Bais et al. 2004). Additionally, microorganisms on the root
surfaces play an important role through the excretion of organic substances
increasing the solubilization of minerals making them available for plant nutri-
tion. It is evident that the environment of the rhizosphere, the ‘root exudate’,
consists of many organic compounds such as organic acid anions,
phytosiderophores, sugars, vitamins, amino acids, purines, nucleosides, inorganic
ions, gaseous molecules, enzymes and root border cells (Dakora and Phillips
7 Coupled Aquaponics Systems 191
Outflow
A Human Domestic Waste Constructed Wetlands
Outflow
B RAS Constructed Wetlands
Aquaculture
C Unit
Hydroponics Unit
Fig. 7.15 Development of coupled aquaponic systems from (a) domestic waste constructed
wetlands (CW) and (b) CW in combination with recirculating aquaculture systems (RAS) to (c)
hydroponic units in coupled aquaponic systems
2002), which may influence the health of aquatic organisms in coupled aquaponic
systems. This symbiotic relationship is not available in either pure aquaculture or
decoupled aquaponics. However, considerable research still needs to be under-
taken to understand the responsible factors for better fish welfare.
Pro: Aquaponics can be considered as an optimized form of the conventional
agricultural production especially in those areas where production factors caused
by the environmental conditions are particularly challenging, e.g. in deserts or
highly populated urban areas (cities). Coupled aquaponic systems can be easily
adjusted to the local conditions, in terms of system design and scale of operation.
Challenge: Coupled aquaponic also show disadvantages, due to often unsuitable
component ratio conditions of the fish and plant production. In order to avoid
192 H. W. Palm et al.
consequences for fish welfare, coupled aquaponic systems must balance the feed
input, stocking density as well as size of the water treatment units and hydropon-
ics. So far knowledge of component ratios in coupled aquaponics is still limited,
and modelling to overcome this problem is at the beginning. Rakocy (2012)
suggested 57 g of feed/day per square meter of lettuce growing area and a
composite ratio of 1 m3 of fish-rearing tank to 2 m3 of pea gravel that allows a
production of 60 kg / m3 tilapia. Based on the UVI-system, the size ratios
themselves were perceived as a disadvantage since a relatively large ratio of
plant growing area to fish surface area of at least 7:3 must be achieved for
adequate plant production. On the other hand, system designs of coupled systems
are highly variable, often not comparable, and the experiences made cannot be
easily transferred to another system or location. Consequently, far more research
data is needed in order to identify the best possible production ratios finally also
enabling upscaling of coupled aquaponic systems through multiplying optimal
designed basic modules (also see Chap. 11).
Challenge: Adverse water quality parameters have been stated to negatively affect
fish health. As Yavuzcan Yildiz et al. (2017) pointed out, nutrient retention of
plants should be maximized to avoid negative effects of water quality on fish
welfare. It is important to select adequate fish species that can accept higher
nutrient loads, such as the African catfish (C. gariepinus) or the Nile tilapia
(O. niloticus,). More sensible species such as the Zander or pikeperch (Sander
lucioperca) might be also applied in aquaponics because they prefer nutrient
enriched or eutrophic water bodies with higher turbidity (Jeppesen et al. 2000;
Keskinen and Marjomäki 2003; [see Sect. 7.7.1. Fish production]). So far, there is
scant data allowing precise statements on fish welfare impairments. With plants
generally needing high potassium concentrations between 230 and 400 mg/L
inside the process water, 200–400 mg/L potassium showed no negative influence
on African catfish welfare (Presas Basalo 2017). Similarly, 40 and 80 mg/L ortho-
P in the rearing water had no negative impact on growth performance, feed
efficiency and welfare traits of juvenile African catfish (Strauch et al. 2019).
Challenge: Another issue is the potential transmission of diseases in terms of food
safety, to people through the consumption of plants that have been in contact with
fish waste. In general, the occurrence of zoonoses is minor because closed
aquaponics are fully controlled systems. However, germs can accumulate in the
process water of the system components or in the fish gut. Escherichia coli and
Salmonella spp. (zoonotic enteric bacteria) were identified as indicators of faecal
contamination and microbial water quality, however, they were detected in
aquaponics only in very small quantities (Munguia-Fragozo et al. 2015). Another
comparison of smooth-textured leafy greens between aquaponics, hydroponics
and soil-based production showed no significant differences in aerobic plate
counts (APC, aerobic bacteria), Enterobacteriaceae, non-pathogenic E. coli and
Listeria, suggesting a comparable contamination level with pathogens (Barnhart
et al. 2015). Listeria spp. was most frequent (40%) in hydroponics with de-rooted
plants (aquaponic plants with roots 0%, aquaponic plants without roots <10%),
but not necessarily the harmful L. monocytogenes species. It was suggested that
7 Coupled Aquaponics Systems 193
the source of the bacteria may be due to the lack of hygiene management, with
little relevance to aquaponics as such. Another infectious bacterium,
Fusobacteria (Cetobacterium), was detected by Schmautz et al. (2017) in the
fish faeces with a high prevalence of up to 75%. Representatives of Fusobacteria
are responsible for human diseases (hospital germ, abscesses, infections),
reproducing in biofilms or as part of the fish intestines. Human infections with
Fusobacteria from aquaponics have not yet been recorded but may be possible by
neglecting the required hygiene protocols.
In general, there is rather little information about diseases caused by the con-
sumption of fish and plants originating from coupled aquaponic systems. In Wilson
(2005), Dr. J.E. Rakocy stated that there was no recorded human disease outbreak in
25 years of coupled aquaponic production. However, a washing procedure of the
plant products should be used to reduce the number of bacteria as a precaution. A
chlorine bath (100 ppm) followed by a potable water rinse was recommended by
Chalmers (2004). If this methodology is used and the contact of the plants or plant
products with the recirculating process water is avoided, the likelihood of contam-
ination with human pathogenic bacteria can be strongly reduced. This is a necessary
precaution not only for coupled but also for all other forms of aquaponics.
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Chapter 8
Decoupled Aquaponics Systems
Simon Goddek, Alyssa Joyce, Sven Wuertz, Oliver Körner, Ingo Bläser,
Michael Reuter, and Karel J. Keesman
8.1 Introduction
Input
shows a traditional one-loop Fish Feed
Top-Up Water
Fertilizer (optional)
Process Water
Output
Fish Crops
Nutrient-Rich Sludge Biowaste
Water Bleed-Off Water (Evapotranspiration)
Brime
Process Water
high pH low pH
Sludge Fertilizer
Output
the sludge and providing it to the plants in a soluble form). Indeed, both the plant
area size and environmental conditions (e.g. surface, leaf area index, relative humid-
ity, solar radiation, etc.) determine the amount of water that can be evapotranspired
and are the main factors determining the rate of RAS water replacement. The water
sent from the RAS to the hydroponic unit is consequently replaced by clean water
which reduces nutrient concentrations and thus improves water quality (Monsees
et al. 2017a, b). The amount of water that can be replaced depends on evapotrans-
piration rate of plants that is controlled by net radiation, temperature, wind velocity,
relative humidity, and crop species. Notably, there is a seasonal dependency, with
more water evaporated in the warmer, sunnier seasons which is also when plant
growth rates are highest. This approach has been suggested by Goddek et al. (2015)
and Kloas et al. (2015) as an approach for improving the design of one-loop systems
and better utilizing capacity to assure optimal plant growth performance. The
concept has been adopted, inter alia, by ECF in Berlin, Germany, and the now
bankrupt UrbanFarmers in The Hague, Netherlands.
Despite potential benefits, initial experiments with a decoupled single-loop
design met with serious drawbacks. This resulted from the high amounts of addi-
tional nutrients that were needed to be added to the hydroponic loop given that the
process water flowing from the RAS to the hydroponics loop is purely evapotrans-
piration dependent (Goddek et al. 2016; Kloas et al. 2015; Reyes Lastiri et al. 2016).
Nutrients also tended to accumulate in the RAS systems when evapotranspiration
rates were lower, and could reach critical levels, thus requiring periodic bleeding off
of water (Goddek 2017).
Overcoming these drawbacks required the implementation of additional loops to
reduce the amount of waste produced in the system (Goddek and Körner 2019). Such
multi-loop systems are outlined in Fig. 8.1c and enhance the two-loop approach
(8.1b) with two units that will be more closely explored in the next two subchapters
as well as Chaps. 10 and 11:
1. Efficient nutrient mineralization and mobilization, using a two-stage anaerobic
reactor system to reduce the discharge of nutrients from the system via fish sludge
2. Thermal distillation/desalination technology to concentrate the nutrient solution
in the hydroponics unit in order to reduce the need for additional fertilizers
Such approaches have been partly implemented by various aquaponics producers
such as the Spanish company NerBreen (Fig. 8.1) (Goddek and Keesman 2018) as
well as Kikaboni AgriVentures Ltd. in Nairobi, Kenya, (van Gorcum et al.
2019) (Fig. 8.2).
In terms of economic advantages (Goddek and Körner 2019; Delaide et al. 2016),
optimizing growth conditions in each respective loop of decoupled aquaponics
systems has inherent advantages for both plants and fish (Karimanzira et al. 2016;
Kloas et al. 2015) by reducing waste discharge as well as improving nutrient
recovery and supply (Goddek and Keesman 2018; Karimanzira et al. 2017; Yogev
et al. 2016). In their work, Delaide et al. (2016), Goddek and Vermeulen (2018), and
Woodcock (pers. Comm.) show that decoupled aquaponics systems achieve better
growth performance than their respective one-loop aquaponics and hydroponics
control groups. Despite this, there are various problems that still need to be resolved,
8 Decoupled Aquaponics Systems 205
Fig. 8.2 Pictures of existing multi-loop system in (1) Spain (NerBreen) and (2) Kenya (Kikaboni
AgriVentures Ltd.). Whereas the NerBreen System is located in a controlled environment, the
Kikaboni System is using a semi-open foil-tunnel system
206 S. Goddek et al.
In RAS, solid and nutrient-rich sludge must be removed from the system to maintain
water quality. By adding an additional sludge recycling loop, accumulating RAS
wastes can be converted into dissolved nutrients for reuse by plants rather than
discarded (Emerenciano et al. 2017). Within bioreactors, microorganisms can break
down this sludge into bioavailable nutrients, which can subsequently be delivered to
plants (Delaide et al. 2018; Goddek et al. 2018; Monsees et al. 2017a, b). Many
one-loop aquaponics systems already include aerobic (Rakocy et al. 2004) and
anaerobic (Yogev et al. 2016) digesters to transform nutrients that are trapped in
the fish sludge and make them bioavailable for plants. However, integrating such a
system into a coupled one-loop aquaponics system has several disadvantages:
1. The dilution factor for nutrient-rich effluents is much higher when discharging
them to a single-loop system in relation to discharging them to the hydroponics
unit only. Effectively, nutrients diluted by entering in contact with large volumes
of fish rearing water.
2. Fish are unnecessarily exposed to the mineralization reactor’s effluents; e.g. the
effluents of anaerobic reactors can include volatile fatty acids (VFAs) and
ammonia that might potentially harm the fish; such reactors also represent an
additional source for potential introduction of pathogens.
3. Around 90% of the nutrients trapped in the sludge can be recovered when RAS
sludge is maintained at a pH of 4 (Jung and Lovitt 2011). Such a low pH is not
possible when operating bioreactors at a pH around 7 (Goddek et al. 2018), which
is the usual trade-off pH value within one-loop aquaponics systems.
With respect to pH, Fig. 8.3 shows the approximate pH values of the respective
process water flows in a multi-loop aquaponics system (e.g. as presented in
Fig. 8.1c). Figure 8.3 also shows the impact of mineralization reactors on the
performance of the system as a whole, based on the anaerobic reactors proposed
by Goddek et al. (2018). Such a system represents only one possible solution for
treating sludge, with alternative approaches discussed in Chap. 10. The decrease in
pH of the process water flowing from the RAS subsystem into the hydroponics loop
as shown in Fig. 8.3 demonstrates acidification in the nutrient concentration loop
(i.e. demineralized water has a pH of 7). Thus, the effluent has a lower pH than the
RAS outlet, which reduces the need to adjust the pH for optimal plant growth
conditions.
8 Decoupled Aquaponics Systems 207
~7 ~6
<6
~7.5
~7.5 ~6
~7 ~7 ~4
~7 ~4
Fig. 8.3 Approximate pH of the water within the different system components as well as the
process water. The ‘~’ indicated an approximation
Table 8.1 Overview of optimal growth conditions for fish and plants and preferred operational
conditions for sludge nutrient recycling treatment
Species/ Nitrate (NO3)
Subsystem function pH Temperature ( C) (mg/L)
Recirculating Oreochromis 7–9 (Ross 27–30 (El-Sayed 2006) <100–200
aquaculture niloticus (Nile 2000) (Dalsgaard et al.
system (RAS) tilapia) 2013)
Oncorhynchus 6.5–8.5 (FAO 15 (Coghlan and <40 (Davidson
mykiss (rainbow 2005) Ringler 2005) et al. 2011;
trout) Schrader et al.
2013)
Hydroponics Lactuca sativa 5.5–6.5 (Resh 21–25 (Resh 2012) 730 (Resh 2012)
(lettuce) 2012)
Lycopersicon 6.3–6.5 (Resh 18–24 (Resh 2002) 666 (Sonneveld
esculentum 2002) and Voogt 2009)
(tomato)
Anaerobic Methanogenesis 6.8–7-4 30–35 (Alvarez and –
reactor (de Lemos Lidén 2008; de Lemos
Chernicharo Chernicharo 2007)
2007)
Sludge 4.0 (Jung and n/a –
mobilization Lovitt 2011)
blanket reactor technology. This has the benefit that (1) biogas is harvested as a
renewable energy source and (2) fewer VFAs are produced in the second stage.
The sludge retention time in the first stage should be several months, before
removing the accumulated nutrients in the sludge (e.g. calcium phosphate aggre-
gation) within the second stage.
• In the second stage, nutrients in suspended solids are effectively mobilized and
become available for plant uptake. This mobilization is the most effective in a
low-pH environment (Goddek et al. 2018; Jung and Lovitt 2011). Once the pH of
acidic reactors is decreased, it usually remains stable; thus less pH regulation is
required in the hydroponic unit.
The effluents that are rich in nutrients may require some post-treatment depending
on the amount of measured total suspended solids and VFAs. However, it is
important to keep in mind that ammonia can stimulate plant growth, e.g. leafy
greens, when it accounts for 5–25% of the total nitrogen concentration (Jones
2005). However, fruit vegetables such as tomatoes or sweet peppers are particularly
sensitive to ammonia in the nutrient solution. An aerobic post-effluent treatment or a
well-aerated hydroponics sump would be required in systems growing those types of
crops.
For system sizing (Sect. 8.4), the amount of water flowing from the RAS system via
the reactor(s) to the hydroponics unit (QMIN) needs to be known (Eq. 8.1):
nfeed ksludge
QMIN ðkg=dayÞ ¼ ð8:1Þ
π sludge
where nfeed is the amount of fish feed in kg, ksludge is the proportion coefficient of fish
feed ending up as sludge, and π sludge is the proportion of total solids (i.e. sludge) in
the sludge water flow entering the mineralization loop.
The sludge concentration can be increased by adding a gravity separation device
prior to the bioreactors, directing the ‘clear’ supernatant back to the RAS system.
This formula can also be used to get an input for sizing the reactor based on the
hydraulic retention time (Chap. 10). Between 20 and 40% of the fish feed ends up as
total suspended solids in the RAS-derived sludge (Timmons and Ebeling 2013). As
an example, it has been found that tilapia sludge contains around 55% of nutrients
that were added to the system via feed (Neto and Ostrensky 2013; Yavuzcan Yildiz
et al. 2017) which represents a valuable resource for crop growth.
The main nutrients that can be recovered via a mineralization process are N and
P. As P (one of the major components of sludge) is the most valuable macronutrient
in terms of cost and availability for crop production, it should be the first element to
be optimized in the aquaponic system.
8 Decoupled Aquaponics Systems 209
where nfeed is the feed input to the system (in kg); π feedis the proportion of the
nutrient in the feed formulation;π sludgeis the proportion of a specific feed-derived
element ending up in the sludge; and ηminis the mineralization and mobilization
efficiency of the reactor system.
The last step would be to determine the concentration of the respective element in
the effluent of the mineralization loop:
Mineralization 1000
Nutrient concentration ðmg=LÞ ¼ ð8:3Þ
QMIN
Example 8.1
Our RAS system is fed with 10 kg of fish feed per day. We assume that 25% of
the fed feed ends up as sludge. In our system, we use a Radial Flow Settler
(RFS) to concentrate the sludge to 1% dry matter. Consequently, the flow from
the RAS to HP via the mineralization loop is calculated as follows:
10kg 0:25
QMIN ðkg=dayÞ ¼ ¼ 250 250kg=day
0:01
We decide to size our system on P. The P content of our feed (in most cases
provided by the feed manufacturer) is 1.5% and 55% of it ends up in the sludge
(Neto and Ostrensky 2013). We assume that our reactors achieve a mineral-
ization efficiency of 90% for this element. Therefore, the grams of P trans-
ferred to the hydroponics unit each day can be determined:
In decoupled aquaponics systems, there is a one-way flow from the RAS to the
hydroponics unit. In practice, plants take up water supplied by RAS, which in turn is
topped up with fresh (i.e. tap or rain) water. The necessary outflow from the RAS
unit is equal to the difference between the water leaving the HP system via plants
(and via the distillation unit) and the water entering the hydroponics unit from the
mineralization reactor, if the system includes a reactor (Fig. 8.4). A simplified
summary is that the long-term water flux requirement from RAS to HP is equal to
the crop water consumption by evapotranspiration and plant water storage in the
plant biomass.
However, in terms of mass balances, the amount of nutrients leaving the hydro-
ponics system via the plants needs to be replaced to assure a constant equilibrium.
This poses a dilemma, as the maximum tolerable nutrient concentration in RAS is
much lower than what is necessary in HP. The high nutrient flows (ρRAS QRAS) for
HP can thus not be accomplished by the low RAS nutrient concentrations. Instead,
without a distillation/desalination loop, the nutrient concentration would increase in
the RAS while decreasing in the hydroponics system. A possible remedy is to
discharge RAS water (and thus also nutrients) to decrease the nutrient concentration
there and add fertilizer to the hydroponics nutrient solution. In terms of environ-
mental and economic impact, this solution is less satisfying and does not serve the
aim of a closed loop combined production.
The implementation of a distillation unit as shown in Fig. 8.3 represents a
potential solution for this dilemma. Such distillation technologies (e.g. thermal
QX Q DIS
Q DIS - QX
Q HP
Q RAS = Q HP + Q X - QMIN
ρRAS ρHP
Q MIN
ρMIN
Fig. 8.4 Scheme of water fluxes and different concentrations of nutrients in a decoupled
aquaponics system, where Q, flow volume in L; ρ, nutrient concentration in mg/L; RAS,
recirculating aquaculture system; MIN, mineralization reactor; DIS, distillation unit; and X,
unknown/flexible flow parameter
8 Decoupled Aquaponics Systems 211
membrane distillation) have the potential to separate dissolved salts and nutrients
from water (Shahzad et al. 2017; Subramani and Jacangelo 2015). In the context of
multi-loop aquaponics systems, and as an alternative to additional fertilization and
water bleed-off with corresponding extra costs, this technology could not only
provide fresh water to the system but also achieve desired nutrient concentrations
for the respective subsystems (Goddek and Keesman 2018).
For the implementation (i.e. sizing) of such a distillation unit, simple mass
balance equations can be used. The remaining system, however, must be sized
beforehand (either via rules of thumb or via mass balance equations; see Sect.
8.5), because the nutrients that enter the system should be in equilibrium with the
bioavailable nutrients taken up by the crop (Note: the sweet spot of decoupled
systems is its flexibility. Consequently, one can also oversize the hydroponics part
of the system although that will necessitate the use of more fertilizer). The easiest
way to estimate nutrient uptake is to use the assumption that nutrients are taken
up/absorbed much the same as dissolved ions in irrigation water (i.e. no element-
specific chemical, biological or physical resistances). Consequently, to maintain
equilibrium, all nutrients taken up by the crop as contained in the nutrient solution
need to be added back to the hydroponics system (Eq. 8.4).
where ϕRAS is the nutrient flow from the RAS system to the hydroponics system,
ϕMIN is the nutrient flow from the mineralization unit to the hydroponics system and
ϕHP is the nutrient plant uptake. For this equation, it is assumed that the distillation
system has an efficiency of close to 100%. Thus, QDIS goes back to the hydroponics
subsystem.
Consequently:
where Q is the flow volume in L, and ρis the nutrient concentration in mg/L.
As stated above, the flow from RAS to the hydroponics unit is the difference of
the sum of the water flows leaving the hydroponics system (i.e. QHP + QX) and the
inflow from the bioreactor (QMIN), i.e. QRAS ¼ QHP + QX QMIN, which leads us to
the following equation:
The targeted variable is the distillation flow (QX) that is required to maintain the
nutrient concentration equilibrium in the hydroponics system. For this, Eq. 8.6 is
solved for QXin the following steps:
212 S. Goddek et al.
Note that the distillation flow QXis highly dynamic and depends on the evapo-
transpiration rate of the plants, which is climate-dependent. The dynamic outcome,
however, can be used for sizing the distillation unit. To calculate the required inflow
into the distillation unit, the following formula can be used:
100
QDIS ¼ QX ð8:9Þ
ηDIS
where Q is the flow volume in L and η the demineralization efficiency of the used
device (in %).
Distillation technology can hence drastically reduce the water and environmental
(i.e. fertilizer usage) footprint of multi-loop aquaponics systems. However,
aquaponics systems become even more complex when considering their implemen-
tation. Even though this additional loop might not make any sense for small-scale
systems, it has the potential to take larger commercial systems to a new level. Yet,
one has to consider that thermal distillation technology requires high amounts of
thermal energy and might not be economically reasonable everywhere. Regions with
high global solar radiation levels or geothermal energy sources might be the most
suitable for this technology. The economical sustainability of such systems is
consequently also location dependent.
Another point to bear in mind is the high temperature of distilled water and brine
from the distillation unit. Depending on the environmental conditions and the fish
species used, the hot distillation water could be used to heat up the RAS water; the
brine, however, needs to cool down before re-entering the HP subsystem.
Sizing an aquaponics system requires balancing the nutrient input and -output. Here,
we basically apply the same principle as sizing a one-loop system. Yet, this approach
is a bit more complicated, but will be fully illustrated with the aid of an example.
Figure 8.5 illustrates the mass balance diagram for our system approach. In the
optimal situation, the system has only one input and output. However, in practice,
one will have to add additional nutrients to the hydroponics part to optimize plant
growth. This model can be used to size the system, e.g. based on phosphorus, which
is a non-renewable resource (Chap. 2). The input to the system (mfeed) is the fraction
8 Decoupled Aquaponics Systems 213
QX
m feed
Q HP x ρ HP
m RAS m HP
ρRAS = ρHP =
V RAS V HP
Q MIN x ρ HP
ρMIN
Fig. 8.5 Scheme that shows the mass balance within a four-loop aquaponics system; where mfeed
are the dissolved nutrients added to the system via feed. Add labels: QDIS - QX to distillate returned
to HP; ‘sludge’ for nutrients entering reactor
of a nutrient that the fish excrete in a dissolved form. The remainder accumulates in
the fish as biomass or ends up as sludge (see previous section). The output is the
plant nutrient uptake. Determining nutrient uptake of plants depends on many factors
and is very complex; the easiest way to give a rough estimate is to consider plant
respiration as the main driver of nutrient uptake (Goddek and Körner 2019).
Evapotranspiration rate is highly climate dependent and is either directly or
indirectly influenced by absorbed shortwave radiation, relative humidity, tempera-
ture, and CO2 concentration. Due to the high complexity of a multi-loop system, we
assume that the plants are located in a climate-controlled greenhouse, and therefore
we only need to consider global radiation as the dynamic variable determining how
much shortwave radiation is absorbed. In other words, we first need to determine
how much of the added nutrients become available for the plants, and then determine
how much the plants actually take up.
The fish feed rate depends on the total biomass in the system and the feed conversion
ratio (FCR). Timmons and Ebeling (2013) provide a simple approach for determin-
ing fish growth rates for different fish species. However, we recommend taking
industrial data to determine the biomass more precisely. Lupatsch and Kissil (1998)
(Eq. 8.10) provide a general growth formula, for which Goddek and Körner (2019)
determined the growth coefficients by curve fitting using the mathematical software
environment MATLAB (internal function ‘fitnlm’) with empirical data for Nile
tilapia (Oreochromis niloticus). Additional initial and final weights, water
214 S. Goddek et al.
Table 8.2 Fish growth parameters for Eq. 8.10 for a given water temperature (T). W0 and Wf can be
adjusted to one’s own needs
Function Parameters Description Value Source
Fish W0 Initial weight of the tilapia For example, Goddek and Körner
growth fingerlings (in g) 55 (2019)
Wf Target harvest weight of the For example, Goddek and Körner
fish (in g) 600 (2019)
T Water temperature of the RAS 30 Timmons and
(in C) Ebeling (2013)
αw; βw; Species-specific growth 0.0261; 0.4071; Goddek and Körner
γw coefficients 0.0827 (2019)
temperature of the system, and the output for the species-specific growth coefficients
can be found in Table 8.2. Inserting these parameters into Eq. 8.10 gives us the
weight at a specific day for this fish species.
h i1β1
1β
W t ¼ W 0 W þ ð1 βW ÞαW expfγ W T gt W ð8:10Þ
where Wt (g) is the fish weight at a specific time (days), W0 (g) is the initial fish
weight, T is the water temperature (in C), αw βw and γw are species-specific growth
coefficients (no units), and t is the time in days.
Based on the output of the equation above, we were able to determine how much
feed the fish will require per growth stage. Most of the times, the feed rate (X% of the
body weight) or FCR is mentioned by the species-specific feed manufacturer.
However, Timmons and Ebeling (2013) provide a rough guideline for FCR for
tilapia: 0.7–0.9 for tilapia that weigh less than 100 g and 1.2–1.3 for tilapia that
weigh more than 100 g. This is done via the following equation.
where FCR is the feed conversion ratio, WGt is the weight gain (per day), and mfish is
the amount of fish in the fish tank.
The weight gain (WG) per day can be determined with Eq. 8.10 by subtracting the
weight of, e.g. day 10 from the weight of day 11. This can be done for each tank.
Figure 8.6 shows the fish feed input to the system for tilapia using the equations
above. The average feed input per day after the system is totally cycled is 165 kg.
Neto and Ostrensky (2013) report a soluble N excretion of 33% and a soluble P
excretion of 17% of feed input when rearing Nile tilapia (Oreochromis niloticus, L.).
8 Decoupled Aquaponics Systems 215
200
Feed rate (kg day-1)
150
100
50
0
1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52
Week of year
Fig. 8.6 Example of biomass balance for tilapia reared in 13 tanks in cohorts with a total volume
(including biofilter and sump) of 482.000 L at a max. Total biomass of 80 t for a period of 2 years
including start-up phase with average fish weight (a) (each line represents one tank/cohort) and the
daily total feed rate (b) (data taken from Goddek and Körner 2019)
These are the nutrients that finally accumulate in the RAS system and can be taken
up by the plants.
Table 8.3 gives an overview of the crop-specific evapotranspiration (ETc) rates that
are linked to global radiation. One mm of ET per square meter equals 1 L. For simple
sizing, one should take the annual daily average (see next section).
Balancing the loops is necessary for sizing the system. The input should be equal to
the output (Fig. 8.5). In a decoupled aquaponics system incorporating a bioreactor
unit, we have two nutrient inflow streams: (1) the fraction of the feed that is
excreted to the RAS system in a soluble form and (2) the fraction of the nutrients
in the fish sludge that the bioreactor(s) manage to mineralize and mobilize. The
major outflow stream (apart from the periodic removal of demineralized sludge) of
nutrients is the nutrient uptake of the plants. The differential Eq. 8.12. expresses
this balance:
216
Table 8.3 Overview of outside global radiation levels subarctic, temperate maritime, and arid conditions (based on Goddek and Körner 2019) and their
respective crop evapotranspiration (ETc, mm day-1) rates for lettuce and tomato grown in a controlled greenhouse environment of 20 C and 80% relative
humidity. Lettuce was cultivated with continuous planting year round; tomato was planted in January and removed in December (Faroe Islands and the
Netherlands) or July and June (Namibia)
Faroe Islands The Netherlands Namibia
Global radiation ETc/lettuce ETc/tomato Global radiation ETc/lettuce ETc/tomato Global radiation ETc/lettuce ETc/tomato
Month mol m2 day1 kg m2 day1 mol m2 day1 kg m2 day1 mol m2 day1 kg m2 day1
January 1.4 0.78 0.52 4.5 0.78 0.53 54.2 2.74 4.55
February 5.2 0.85 1.38 9.1 0.93 1.40 53.7 2.70 4.47
March 13.7 1.20 2.12 17.0 1.28 2.14 51.2 2.42 3.96
April 30.6 1.90 3.05 27.9 1.82 2.90 40.2 3.05 5.38
May 39.2 2.29 3.57 32.2 2.40 3.74 30.0 2.70 4.59
June 39.6 2.33 3.60 36.6 2.52 3.91 30.5 2.28 3.80
July 34.5 2.17 3.37 36.4 2.54 3.94 32.1 2.40 1.76
August 21.3 1.67 2.73 31.7 2.28 3.51 37.5 2.61 3.92
September 13.2 1.20 2.04 23.1 1.75 2.77 43.2 2.00 3.02
October 6.0 0.91 1.77 13.3 1.17 1.94 51.6 2.07 3.09
November 2.1 0.78 1.60 6.2 0.87 1.62 57.9 2.30 3.58
December 0.4 0.79 1.66 3.5 0.77 1.52 59.8 2.44 3.95
Average 17.3 1.41 2.28 20.6 1.59 2.50 45.6 2.47 3.83
S. Goddek et al.
8 Decoupled Aquaponics Systems 217
QHP ρHP
Mineralization ðEq:8:2Þ þ mfeed ¼ ð8:12Þ
1000
QHP ρHP
nfeed 1000 π feed π sludge ηmin þ mfeed ¼ ð8:13Þ
1000
where nfeed is the average feed (in kg) entering the RAS system, π feedis the proportion
of the nutrient in the feed formulation, π sludge is the proportion of a specific feed-
derived element ending up in the sludge, and ηmin is the mineralization and mobi-
lization efficiency of the reactor system, mfeed is the average amount of a nutrient that
the fish defecate in a dissolved form, QHP is the average total evapotranspiration, and
ρHPis the target (i.e. optimal) nutrient concentration for a specific nutrient in the
hydroponic subsystem.
However, to be able to determine the required area, there are two variables that
need to be redefined in order to solve this equation. Equation 8.14 shows how to
calculate the soluble nutrient excretion. In Eq. 8.15, we show that the average total
evapotranspiration is a product of the area and the plant-specific evapotranspiration
rate (here shown as an average) per m2.
where ηexcr represents the fraction of the nutrient excreted by the fish in a
soluble form.
QHP ¼ A ET c ð8:15Þ
where QHP represents the average total evapotranspiration (in L), A the area, and
ET c the average crop-specific evapotranspiration in mm/m2 (i.e. L/m2).
Solving Eq. 8.13 by incorporating Eqs. 8.14 and 8.15 to find A, we are able to
calculate the required plant area with respect to the average feed input (Eq. 8.15).
nfeed 1000 π feed ηexcr 1000 þ nfeed 1000 π feed π sludge ηmin 1000
A¼
ET c ρHP
ð8:16Þ
218 S. Goddek et al.
Example 8.2
For this example, we want to size (i.e. balance) the system with respect to
P. We assume that the RAS component of our system requires an average daily
feed input of 150 kg. The manufacturer reports the P content of the fish feed to
be 1%. We estimate the P ending up in the sludge to be 55% and the P that fish
excrete in a soluble form to be 17%. The bioreactors perform quite well and
mineralize around 85% of the P.
On the output side, we calculated the average crop-specific evapotranspi-
ration rate for lettuce (by, e.g. using the FAO Penman-Monteith equation). At
our location, it is around 1.3 mm/day (i.e. 1.3 L/day). The optimal P compo-
sition of the nutrient solution is reported to be 50 mg/L (Resh 2013). Finding
the area of plant cultivation needed to uptake the P produced by the system is
then solved by:
nfeed 1000 π feed ηexcr 1000 þ nfeed 1000 π feed π sludge ηmin 1000
A¼
ET c ρHP
The example above shows that the majority of the P in the hydroponics unit
originates from the bioreactors. Thus, implementation of a bioreactor within a
decoupled system has a very high impact on P sustainability. By contrast, in order
to size simple one-loop aquaponics systems, a rule of thumb is usually applied. For
leafy plants approx. 40–50 g and for fruity plants approx. 50–80 g of feed is required
per m2 cultivation area (FAO 2014). When looking at the feed input in the given
example above ¼ 150 kg, and dividing it by 45 (the average of the leafy plant
approximation), the proposed cultivation area is around 3750 m2. Leaving out the
sludge mineralization, our example would suggest a cultivation area of 3333 m2
when sizing the system on P.
The role of the distillation unit is to keep the nutrient concentration of the RAS
system and the hydroponics system at their respective desired levels. Since nutrient
accumulation and the corresponding specific nutrient density are dynamic in RAS
systems (i.e. depending on the ETc rates) that depend on the QHP and QX flow
(Fig. 8.5), the size of the distillation unit cannot be determined using a differential
8 Decoupled Aquaponics Systems 219
200 150
NO3-N (ppm) RAS
PO4-P (ppm) HP
(a) Namibia 0 L h-1
150 5000L h-1
0 L h-1 100
100 5000L h-1
50
50
0 0
7 8 9 101112 1 2 3 4 5 6 7 8 9 101112 1 2 3 4 5 6 7 8 9 101112 1 2 3 4 5 6
200 150
NO3-N (ppm) RAS
PO4-P (ppm) HP
(b) Netherlands
150
100
100
50
50
0 0
1 2 3 4 5 6 7 8 9 10 1112 1 2 3 4 5 6 7 8 9 101112 1 2 3 4 5 6 7 8 9 101112
Fig. 8.7 Simulations comparing NO3-N concentration in the RAS water system on the impact of
distillation flows (no, solid line; 5000 L h-1, dashed line) on hydroponics (yellow, ---) and RAS
(blue, ---) nutrient solution concentrations in (a) Namibia and (b) the Netherlands, i.e. in low and
high latitudes (Namibia 22.6 S and the Netherlands, 52.1 N, respectively) within a 36-month
period (including the system run-up phase) using local climate data and climate-adjusted green-
houses as model input
equation. Thus, a time series model is required to determine the nutrient concentra-
tion in the RAS over time. The nutrient concentration at a specific time is necessary
to be able to execute mass balance equations within the system (Sect. 8.3).
For the system to be balanced (i.e. input ¼ output), we can give a general
guideline on the required capacity of such a distillation unit. The objective is to
avoid nutrient accumulation in the RAS system. Figure 8.7a, b shows the impact of
distillation flows on the hydroponics and RAS nutrient solution without a mineral-
ization loop in two different latitudes. Both systems have the same feed input
(in average 158.6 kg day1; see Fig. 8.6). However, by taking the environmental
conditions and climate-adjusted greenhouses into account, the necessary and optimal
hydroponic area differs between geographical locations (see Chap. 11). Hydroponic
systems with low potential evaporation rates, as are common in locations at high
latitudes (i.e. far from the equator) would need larger cultivation areas than places
closer to the equator. At the same time, a higher annual variation in irradiation and
thus transpiration is common in these regions, thus a higher demand on seasonal
variability on water and nutrients is present (see Fig. 8.7). In greenhouse cultivation,
however, supplementary lighting may be necessary, and in countries such as Nor-
way, vegetable cultivation without supplementary lighting hardly takes place. In
addition, the total crop leaf surface makes a difference; crops with a high leaf area
per unit ground area (i.e. leaf area index) transpire more than crops with smaller leaf
areas, and a distinct difference can be seen between tomato and lettuce crops. All of
these factors need to be considered when planning and sizing the aquaponic system.
220 S. Goddek et al.
250
NNO3-N (ppm)
Tomato Young Plants Tomato Young Plants
200 (a) Faroer Islands Tomato
Lettuce
150 Start-Phase Summer
100
50 Winter Winter
0
1 2 3 4 5 6 7 8 9 101112 1 2 3 4 5 6 7 8 9 101112 1 2 3 4 5 6 7 8 9 101112
250
NNO3-N (ppm)
250
NNO3-N (ppm)
Fig. 8.8 NO3-N in RAS combined with HP growing tomato or lettuce in three climate zones and
decreasing latitudes (Faroe Islands 62.0 N, the Netherlands 52.1 N, Namibia 22.6 S) with opti-
mized area for hydroponics (see above) in a 36-month simulation using local climate data and
climate-adjusted greenhouses as model input
will occur. Based on Goddek and Körner (2019), we show the variation of NO3-N in
RAS for tomato (often not adjusted in aquaponics) and lettuce when no supplemen-
tary lighting is used for three climate zones (Faroe Islands, the Netherlands, and
Namibia) (Fig. 8.8). System balance is achievable by increasing the daily light
integral (i.e. sum of mol light received during a 24-h period) with dynamic supple-
mentary lighting control (Körner et al. 2006).
Applying distillation/desalination technologies can contribute to significant
reductions in nutrient levels in the RAS while adjusting levels in the HP system
closer to optima, i.e. the unit concentrates nutrients to levels required by plants.
Figure 8.9 illustrates the effect of a desalination unit on RAS NO3-N concentration
when applying between 0 and 5000 L h1 and system1. It is obvious that with
increasing desalination flux, the NO3-N concentration in the RAS system is decreas-
ing. The unit, however, is controlled by the demand of PO4 in the HP system. Peaks
need to be avoided and, as stated above, this can be achieved by creating a stable
climatic environment with dynamic light controls. It is obvious that in climate
regions with fewer annual differences in solar radiation, there is less variation in
ETc and the complete system is more stable. Installing lamps and keeping a daily
light integral of at least 10 mol m2 can compensate for seasonal variations.
Interplanting and mixed crop production help level the peak resulting from the
traditional tomato cultivation protocol with young plants in winter when both
222 S. Goddek et al.
NO3-N (ppm)
NO3-N (ppm)
250 250
200 (a) Faroer Islands 0 200 0
1000 1000
150 2000 150 2000
100 3000 100 3000
4000 4000
50 5000 50 5000
0 0
2 4 6 8 1012 2 4 6 8 1012 2 4 6 8 1012 2 4 6 8 1012 2 4 6 8 1012 2 4 6 8 1012
NO3-N (ppm)
NO3-N (ppm)
250 250
200 (b) Netherlands 200
150 150
100 100
50 50
0 0
2 4 6 8 1012 2 4 6 8 1012 2 4 6 8 1012 2 4 6 8 1012 2 4 6 8 1012 2 4 6 8 1012
Month Month
NO3-N (ppm)
NO3-N (ppm)
250 250
200 (c) Namibia 200
150 150
100 100
50 50
0 0
8 1012 2 4 6 8 10 12 2 4 6 8 10 12 2 4 6 8 1012 2 4 6 8 10 12 2 4 6 8 10 12 2 4 6
Fig. 8.9 NO3-N in RAS combined with HP with tomato (right) or lettuce (left) with desalination
between 0 and 5000 L h 1 supply in three climate zones and decreasing latitudes (Faroe Islands
62.0 N, the Netherlands 52.1 N, Namibia 22.6 S) with adjusted area for HP (see above) in a 36-
month simulation using local climate data and climate-adjusted greenhouses as model input
climate (low radiation) and cultivation (small plants, low potential ETc) contribute to
nutrient accumulation.
r ε u y
C P
+
-
Fig. 8.10 Feedback control with controller (C) and process (P). r reference signal, eps tracking
error, u input signal, y output sigma
unknown random inputs and measurement noise. Moreover, the overall process (P)
may change over time as a result of growth, maturation, senescence, etc. Fish feed is
another input into the RAS and its effect on fish growth cannot be directly seen or
measured. For these parameters, model-based controllers (e.g. feedforward, model
predictive, and optimal control) are typically introduced to predict the response of a
change in the control input. However, fish feed is commonly added on the basis of
values found in tables or recipes, but this rule-based control may need some
adjustment in real practice to act as a feedback controller. Fish behaviours in RAS
are a classical feedback control measure as fish react physiologically to environ-
mental changes with variations in movement, location, receptiveness to feed, etc.
Hydroponic production usually takes place in protected environments such as
greenhouses or plant factories where both the root and aerial environment need to be
controlled. On-off controllers that predictively model optimal aerial environments
have been proven superior in experimental research, but commercialization has been
slow, whereas feedback controllers are standard in most climate-controlled green-
houses. However, the actuator varies with the type of controller with heating valves
and vents typically feedback-controlled but lighting usually having an ON-OFF
mechanism and only a few being dimmable. Controllers that rely on sensor or data
input can respond to fast growth in a protected environment and result in high-
quality produce with high market prices that improves its cost benefits. Many
commercial greenhouses still have the classical centrally located sensor hanging
1–2 m above the crop and covering several hundred square meters is still in use, but
multiple wireless sensors covering smaller areas are being introduced although much
of the detailed data cannot be used because rather large climatic zones are controlled
by the same actuators. Advances in sensor technology (e.g. microclimate tempera-
ture sensors, image processors, real-time gas-exchange or chlorophyll fluorescence
measurements) connected to modelling software could use decision-support systems
and become automated control systems.
In typical bioreactor systems, temperature, pH, dissolved oxygen in aerated
systems, and gas fluxes in anaerobic systems are continuously measured and
adjusted with available temperature, pH, and dissolved oxygen controllers. In
addition to this, both hydraulic (HRT) and sludge retention (SRT) times are also
frequently set by controlling (waste)water flows and biomass waste flows,
respectively.
224 S. Goddek et al.
Technologies that generate less profit, but are better for the environment usually only
get implemented when the operators either receive an incentive in the form of
subsidies or policies force them to do so. In the case of one-loop aquaponics systems,
the appeal lies in the novel technology and the system’s approach to sustainable
resource use rather than its economic potential. However, recent publications pro-
vide evidence for production gains: leafy greens grow better in decoupled environ-
ments than in sterile hydroponic systems (Delaide et al. 2016; Goddek and
Vermeulen 2018) and lettuce in decoupled aquaponics systems had a growth
advantage of approximately 40% compared to state-of-the-art hydroponic
approaches.
Even though higher growth rates can be expected, multi-loop aquaponics systems
are still far more complex than hydroponics systems and significant initial invest-
ments are required for implementation. Most geographic locations require a high-
tech greenhouse to control environmental conditions (i.e. a relative humidity of 80%,
constant temperatures of around 20 C). Renewable energy sources can be used for
cooling and heating, but currently such systems are only profitable when setting up
on a large scale (i.e. > 1 ha) where good market conditions prevail.
Based on Example 8.2, there is evidence that treating sludge in digesters can have a
beneficial impact on nutrient reutilization, especially phosphorus. Bioreactor sys-
tems, such as a sequential two-stage UASB reactor system, can increase the phos-
phorus recycling efficiency up to 300% (Chap. 10). Previously, in Chap. 2, we
discussed the phosphorus paradox in relation to both phosphate scarcity and prob-
lems with eutrophication. Bioreactors have significant advantages for increased
nutrient recovery from sludge, thus helping to close the nutrient cycling loop within
aquaponics systems. However, further research is needed to refine such systems to
optimize the bioavailability of specific nutrients. Figures 8.11, 8.12, and 8.13 show
the input, output, and waste streams of stand-alone aquaculture and hydroponics
systems compared with a decoupled aquaponics system. It can be seen that the
decoupled approach constitutes a promising agricultural concept for a waste reduc-
tion and recycling system.
8 Decoupled Aquaponics Systems 225
Hydroponics
Input Output
Fertilizer/ Plants
Micronutrients
Biowaste
Water
Hydroponics
Loss
Pollution
Fig. 8.11 Input, output, and loss streams in a stand-alone hydroponic system
Aquaculture
Input Output
Fingerlings Fish
Water
Aquaculture
Fish Feed:
Protein
Phosphorus
Potassium
Other Minerals
Loss
Pollution
Fig. 8.12 Input, output, and loss streams in a stand-alone aquaculture system
226 S. Goddek et al.
Decoupled Aquaponics
Input Output
Fertilizer/ Plants
Micronutrients
Biowaste
Hydroponics
Methane
Demineralized
Sludge
Nutrient Anaerobic
Concentration Digestion
Fingerlings Fish
Water
Aquaculture
Fish Feed:
Protein
Phosphorus
Potassium
Other Minerals
Loss
Pollution
Fig. 8.13 Input, output, and loss streams in a decoupled multi-loop aquaponics system comprising
an anaerobic reactor system
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Chapter 9
Nutrient Cycling in Aquaponics Systems
Abstract In aquaponics, nutrients originate mainly from the fish feed and water
inputs in the system. A substantial part of the feed is ingested by the fish and either
used for growth and metabolism or excreted as soluble and solid faeces, while the
rest of any uneaten feed decays in the tanks. While the soluble excretions are readily
available for the plants, the solid faeces need to be mineralised by microorganisms in
order for its nutrient content to be available for plant uptake. It is thus more
challenging to control the available nutrient concentrations in aquaponics than in
hydroponics. Furthermore, many factors, amongst others pH, temperature and light
intensity, influence the nutrient availability and plant uptake. Until today, most
studies have focused on the nitrogen and phosphorus cycles. However, to ensure
good crop yields, it is necessary to provide the plants with sufficient levels of all key
nutrients. It is therefore essential to better understand and control nutrient cycles in
aquaponics.
9.1 Introduction
aquaponics has two main advantages for nutrient cycling. First, the combination of a
recirculating aquaculture system with hydroponic production avoids the discharge of
aquaculture effluents enriched in dissolved nitrogen and phosphorus into already
polluted groundwater (Buzby and Lin 2014; Guangzhi 2001; van Rijn 2013), and
second, it allows for the fertilisation of the soilless crops with what can be considered
an organic solution (Goddek et al. 2015; Schneider et al. 2004; Yogev et al. 2016)
instead of using fertilisers of mineral origin made from depleting natural resources
(Schmautz et al. 2016; Chap. 2). Furthermore, aquaponics yields comparable plant
growth as compared with conventional hydroponics despite the lower concentrations
of most nutrients in the aquaculture water (Graber and Junge 2009; Bittsanszky et al.
2016; Delaide et al. 2016), and production can be even better than in soil (Rakocy
et al. 2004). Increased CO2 concentrations in the aerial environment and changes in
the biomes of the root zone are thought to be main reasons for this. In addition, the
mineral content and the nutritional quality of tomatoes grown aquaponically have
been reported to be equivalent or superior to the mineral content of conventionally
grown ones (Schmautz et al. 2016).
Despite having two attractive assets (i.e. the recycling of aquaculture effluents and
the use of organic fertilisers), the use of aquaculture effluents increases the challenge
of monitoring the nutrients within the solution. Indeed, it is harder to control the
composition of a solution where the nutrients originate from a biological degradation
of organic matter than to follow the evolution of the nutrients’ concentration in a
precisely dosed hydroponic solution based on mineral compounds (Bittsanszky et al.
2016; Timmons and Ebeling 2013). Moreover, a plant’s nutritional needs vary during
the growth period in accordance with physiological stages, and it is necessary to meet
these needs to maximise yields (Bugbee 2004; Zekki et al. 1996; Chap. 4).
In order to recycle aquaculture effluents to produce plant biomass, it is necessary
to optimise the recycling rates of phosphorus and nitrogen (Goddek et al. 2016;
Graber and Junge 2009; Chap. 1). Several factors can influence this, such as the fish
species, fish density, water temperature, the type of plants and the microbial com-
munity (ibid.). Therefore, it is of prime importance to understand the functioning of
the nutrient cycles in aquaponics (Seawright et al. 1998). This chapter aims at
explaining the origins of the nutrients in an aquaponic system, describing the
nutrient cycles and analysing the causes of nutrient losses.
The major sources of nutrients in an aquaponic system are the fish feed and the water
added (containing Mg, Ca, S) (see Sect. 9.3.2.) into the system (Delaide et al. 2017;
Schmautz et al. 2016) as further elaborated in Chap. 13. With respect to fish feed,
there are two main types: fishmeal-based and plant-based feed. Fishmeal is the
classic type of feed used in aquaculture where lipids and proteins rely on fish meal
and fish oil (Geay et al. 2011). However, for some time now, concerns regarding the
sustainability of such feed have been raised and attention drawn towards plant-based
9 Nutrient Cycling in Aquaponics Systems 233
diets (Boyd 2015; Davidson et al. 2013; Hua and Bureau 2012; Tacon and Metian
2008). A meta-analysis conducted by Hua and Bureau (2012) revealed that the use of
plant proteins in fish feed can influence the growth of fish if incorporated in high
proportions. Indeed, plant proteins can have an impact on the digestibility and levels
of anti-nutritional factors of the feed. In particular, phosphorus originating from
plants and thus in the form of phytates does not benefit, for example, salmon, trout
and several other fish species (Timmons and Ebeling 2013). It is not surprising that
this observation is highly dependent on the fish species and on the quality of the
ingredients (Hua and Bureau 2012). However, little is known of the impact of
varying fish feed composition on crop yields (Yildiz et al. 2017).
Classical fish feed is composed of 6–8 macro ingredients and contains 6–8%
organic nitrogen, 1.2% organic phosphorus and 40–45% organic carbon (Timmons
and Ebeling 2013) with around 25% protein for herbivorous or omnivorous fish and
around 55% protein for carnivorous fish (Boyd 2015). Lipids can be fish or plant
based as well (Boyd 2015).
Uneaten Feed Faeces Soluble Excretion Uneaten Feed Faeces Soluble Excretion
18% N 13% N 33% N 5-13% N 60-86% N 34% N
18% P 37% P 17% P 20% P 30% P
Neto and Ostrensky 2015 Timmons and Ebeling citing Chen et al. 1993
Yogev et al. 2017
Schneider et al. 2004 (any Fish)
Fig. 9.1 Environmental flow of nitrogen and phosphorus in % for (a) Nile tilapia cage production
(after Neto and Ostrensky 2015) and (b) RAS production (from a variety of sources)
234 M. Eck et al.
Once fish feed is added into the system, a substantial part of it is eaten by the fish
and either used for growth and metabolism or excreted as soluble and solid faeces,
while the rest of the given feed decays in the tanks (Goddek et al. 2015; Schneider
et al. 2004) (Fig. 9.1). In this case, the feed leftovers and metabolic products are
partly dissolved in the aquaponic water, thus enabling the plants to uptake nutrients
directly from the aquaponic solution (Schmautz et al. 2016).
In most cultivation systems (Chaps. 7 and 8), nutrients can be added to
complement the aquaponic solution and ensure a better matching with the plants’
needs (Goddek et al. 2015). Indeed, even when the system is coupled, it is possible to
add iron or potassium (which are often lacking) without harming the fish (Schmautz
et al. 2016).
Ideally, all the given feed should be consumed by the fish (Fig. 9.1). However, a
small part (less than 5% (Yogev et al. 2016)) is often left to decompose in the system
and contributes to the nutrient load of the water (Losordo et al. 1998; Roosta and
Hamidpour 2013; Schmautz et al. 2016), thus consuming dissolved oxygen and
releasing carbon dioxide and ammonia (Losordo et al. 1998), amongst other things.
The composition of fish feed leftovers depends on the composition of the feed.
Logically enough, the composition of fish faeces depends on the fish’s diet which
also has an impact on the water quality (Buzby and Lin 2014; Goddek et al. 2015).
However, the nutrient retention in fish biomass is highly dependent on fish species,
feeding levels, feed composition, fish size and system temperature (Schneider et al.
2004). At higher temperatures, for example, fish metabolism is accelerated and thus
results in more nutrients contained in the solid fraction of the faeces (Turcios and
Papenbrock 2014). The proportion of excreted nutrients also depends on the quality
and digestibility of the diet (Buzby and Lin 2014). The digestibility of the fish feed,
the size of the faeces and the settling ratio should be carefully considered to ensure a
good balance in the system and to maximise crop yields (Yildiz et al. 2017). Indeed,
while it is a priority that fish feed should carefully be chosen to suit fish needs, the
feed components could also be selected to suit plant’s requirements when it makes
no difference to fish (Goddek et al. 2015; Licamele 2009; Seawright et al. 1998).
9.3.1 Solubilisation
aquaculture (Sugita et al. 2005; Turcios and Papenbrock 2014) and aquaponics,
solubilisation is conducted mainly by heterotrophic bacteria (van Rijn 2013;
Chap. 6) which have not yet been fully identified (Goddek et al. 2015). Some studies
have started deciphering the complexity of these bacteria communities (Schmautz
et al. 2017). In current aquaculture, the most commonly observed bacteria are
Rhizobium sp., Flavobacterium sp., Sphingobacterium sp., Comamonas sp.,
Acinetobacter sp., Aeromonas sp. and Pseudomonas sp. (Munguia-Fragozo et al.
2015; Sugita et al. 2005). An example of the major role of bacteria in aquaponics
could be the transformation of insoluble phytates into phosphorus (P) made available
for plant uptake through the production of phytases which are particularly present in
γ-proteobacteria (Jorquera et al. 2008). (More research needs to be done in this
area). Other nutrients than P can also be trapped as solids and evacuated from the
system with the sludge. Efforts are thus being made to remineralise this sludge with
UASB-EGSB reactors in order to reinject nutrients into the aquaponic system
(Delaide 2017; Goddek et al. 2016; Chap. 10). Furthermore, different minerals are
not released at the same rate, depending on the composition of the feed (Letelier-
Gordo et al. 2015), thus leading to more complicated monitoring of their concen-
tration in the aquaponic solution (Seawright et al. 1998).
9.3.2 Nitrification
The main nitrogen source in an aquaponic system is the fish feed and the proteins it
contains (Goddek et al. 2015; Ru et al. 2017; Wongkiew et al. 2017; Yildiz et al.
2017). Ideally, 100% of this feed should be eaten by the fish. However, is has been
observed that fish only use about 30% of the nitrogen contained in the given feed
(Rafiee and Saad 2005). The ingested feed is partly used for assimilation and
metabolism (Wongkiew et al. 2017), while the rest is excreted either through the
gills or as urine and faeces (Ru et al. 2017). The nitrogen which is excreted through
the gills is mainly in the form of ammonia, NH3 (Wongkiew et al. 2017; Yildiz et al.
2017), while urine and faeces are composed of organic nitrogen (Wongkiew et al.
2017) which is transformed into ammonia by proteases and deaminases (Sugita et al.
2005). In general, the fish excrete nitrogen under the form of TAN, i.e. NH3 and
NH4+. The balance between NH3 and NH4+ depends mostly on the pH and temper-
ature. Ammonia is the major waste produced by fish catabolism of the feed proteins
(Yildiz et al. 2017).
Nitrification is a two-step process during which the ammonia NH3 or ammo-
nium NH4+ excreted by the fish is transformed first into nitrite NO2 and then into
nitrate NO3 by specific aerobic chemosynthetic autotrophic bacteria. A high
availability of dissolved oxygen is required as nitrification consumes oxygen
(Carsiotis and Khanna 1989; Madigan and Martinko 2007; Shoda 2014). The
first step of this transformation is carried out by ammonia-oxidising bacteria
(AOB) such as Nitrosomonas, Nitrosococcus, Nitrosospira, Nitrosolobus and
Nitrosovibrio. The second step is conducted by nitrite-oxidising bacteria (NOB)
236 M. Eck et al.
9.4.1 Context
Carbon (C)
Carbon is provided to the fish via the feed (Timmons and Ebeling 2013) and to the
plants via CO2 fixation. Fish can use 22% of the carbon contained in the fish feed for
biomass increase and metabolism. The rest of the ingested carbon is either expirated
under the form of CO2 (52%) or excreted in a dissolved (0.7–3%) and solid (25%)
form (Timmons and Ebeling 2013). The expirated CO2 can be used by plants for
their own carbon source as well (Körner et al. 2017). The uneaten part of the feed
carbon is left to decompose in the system. The type of carbohydrates found in fish
feed (e.g. starch or non-starch polysaccharides) can also influence the digestibility of
the feed and the biodegradability of the waste in an aquaculture or aquaponic system
(Meriac et al. 2014).
Nitrogen (N)
Nitrogen is absorbed by the plants either in the nitrate or ammonium form
(Sonneveld and Voogt 2009; Xu et al. 2012) depending on the concentration and
plant’s physiology (Fink and Feller 1998 cited by Wongkiew et al. 2017). Associ-
ations between plants and microorganisms should not be overlooked as plants affect
the presence of the microorganisms in aquaponics, and microorganisms can play a
significant role in the nitrogen uptake capacity of plants (Wongkiew et al. 2017). The
uptake of nitrogen by plants is affected by the ambient carbon dioxide concentration
(Zhang et al. 2008 cited by Wongkiew et al. 2017).
Phosphorus (P)
Phosphorus is one of the essential elements for plant growth and can be absorbed
under its ionic orthophosphate form (H2PO4 , HPO42 , PO43 ) (Prabhu et al.
2007; Resh 2013). Little is known about the dynamics of phosphorus in
aquaponics. The main input of phosphorus in the system is the fish feed (Cerozi
and Fitzsimmons 2017; Delaide et al. 2017; Schmautz et al. 2015), and in
un-supplemented systems (Chap. 7), phosphorus tends to be limiting and thus
can impede plant growth (Graber and Junge 2009; Seawright et al. 1998).
According to Rafiee and Saad (2005), fish can use up to 15% of the phosphorus
contained in the feed. In a system growing lettuce, Cerozi and Fitzsimmons (2017)
noticed that the amount of phosphorus provided by the fish feed can be sufficient
or insufficient depending on the growth stage. Up to 100% of phosphorus present
in the fish water can be recycled in the plant biomass, depending on the design of
the system. Graber and Junge (2009) observed a 50% recycling, while Schmautz
et al. (2015) reported that 32% of the phosphorus could be found in the fruit and
28% in the leaves. The solubility of phosphorus depends on the pH, and a higher
pH will foster the precipitation of phosphorus, thus rendering it unavailable for
the plants (Yildiz et al. 2017). Phosphorus can precipitate as struvite (magnesium
ammonium phosphate) (Le Corre et al. 2005) and/or hydroxyapatite (Cerozi and
9 Nutrient Cycling in Aquaponics Systems 239
Fitzsimmons 2017; Goddek et al. 2015). These insoluble complexes are removed
via solid fish sludge from the system. Schneider et al. (2004) reported that
30–65% of the phosphorus contained in the fish feed remains unavailable to
plants as it is fixed in the solid excretions which are then removed through
mechanical filtration. Yogev et al. (2016) estimated that this loss can be up to
85%. One option to prevent this massive loss of P via solid sludge is to add a
digestion compartment to the aquaponic system. During aerobic or anaerobic
digestion, the P is released into the digestate and could be re-introduced into the
circulating water (Goddek et al. 2016).
Potassium (K)
Delaide et al. (2017) found that the major source of K in their system was the fish
feed. Fish can use up to 7% of the K contained in the fish feed (Rafiee and Saad
2005). However, potassium is not necessary for fish which leads to a low potassium
composition of the fish feed and to even lower levels of potassium available for the
plants (Graber and Junge 2009; Seawright et al. 1998; Suhl et al. 2016). To supply
potassium, a KOH pH buffer is often used as the pH often decreases in aquaponics
due to nitrification (Graber and Junge 2009). In an aquaponic system planted with
tomatoes, potassium accumulated mainly in the fruits (Schmautz et al. 2016).
Magnesium (Mg), Calcium (Ca) and Sulphur (S)
The main source for Mg, Ca and S is tap water which facilitates the absorption by the
plants as the nutrients are already available (Delaide et al. 2017). Calcium is however
present in insufficient levels in aquaponics (Schmautz et al. 2015; Seawright et al.
1998) and is added under the form of calcium hydroxide Ca(OH)2 (Timmons and
Ebeling 2013). According to Rafiee and Saad (2005), fish can use on average 26.8%
of the calcium and 20.3% of the magnesium present in the feed. Sulphur is often at
low levels in aquaponic systems (Graber and Junge 2009; Seawright et al. 1998).
Iron (Fe), manganese (Mn) and zinc (Zn) derive mainly from the fish feed, while
boron (B) and copper (Cu) derive from the tap water (Delaide et al. 2017). In
aquaponics, key micronutrients are often present but at too low levels (Delaide
et al. 2017), and supplementation from external sources of nutrients is then necessary
(Chap. 8). Iron deficiencies occur very often in aquaponics (Schmautz et al. 2015;
Seawright et al. 1998; Fitzsimmons and Posadas; 1997 cited by Licamele 2009),
mostly because of the non-availability of the ferric ion form. This deficiency can be
solved by the use of bacterial siderophore (i.e. organic iron-chelating compounds)
produced by genera such as Bacillus or Pseudomonas (Bartelme et al. 2018) or by
iron supplementation with chemical chelated iron to avoid iron precipitation.
240 M. Eck et al.
size of the hydroponic area to the fish tanks, biofilters and other equipment can be
calculated (Goddek and Körner 2019). This is particularly important with decoupled
multi-loop systems which comprise various types of equipment. For example,
UASB (upflow anaerobic sludge blanket) (Goddek et al. 2018) or desalination
units (Goddek and Keesman 2018) need to be sized carefully as discussed in
Chap. 8. The basic mismatch of nutrients supplied by the fish environment and the
needs of the crops needs to be rectified and balanced. For the purpose of
up-concentrating the nutrients, Goddek and Keesman (2018) have described an
appropriate desalination unit (Chap. 8). This approach, however, only solves part
of the problem, as the perfectly balanced system is driven by a non-dynamic
evaporation rate achievable only in closed chambers and perfectly working plants.
The reality, however, is that the evapotranspiration of the crop (ETc) in greenhouse-
based aquaponics systems is highly dependent on multiple factors such as physical
climate and biological variables. ETc is calculated per area of the ground surface
covered by the crop and is calculated for different levels in the canopy (z) by
integrating irradiative net fluxes, boundary layer resistance, stomata resistance and
the vapour pressure deficit, in the canopy (Körner et al. 2007) using the Penman–
Monteith equation. This equation, nevertheless, only calculates the water flux
through the crop. Nutrient uptake can either be calculated simply by assuming that
all diluted nutrients in the water are taken up by the crop. In reality though, uptake of
nutrients is a highly complicated matter. Different nutrients have different states,
changing with parameters such as pH. Meanwhile nutrient availability to the plants
strongly depends on pH and the relationships of nutrients to each other (e.g. K/Ca
availability). In addition, the microbiome in the root zone plays an important role
(Orozco-Mosque et al. 2018) which is not yet implemented in models although some
models differentiate between phloem and xylem pathways. Thus, the vast amount of
nutrients is not modelled in detail for aquaponic nutrient balancing and sizing of
systems. The easiest way to estimate nutrient uptake is the assumption that nutrients
are taken up/absorbed as dissolved in irrigation water and apply to the above-
explained ETc calculation approach and assuming that no element-specific chemical,
biological or physical resistances exist. Consequentially, to maintain equilibrium, all
nutrients taken up by the crop as contained in the nutrient solution need to be added
back to the hydroponic system.
9.5 Conclusions
In hydroponics, the nutrient solution is accurately determined and the nutrient input
into the system is well understood and controlled. This makes it relatively easy to
adapt the nutrient solution for each plant species and for each growth stage. In
aquaponics, according to the definition (Palm et al. 2018), the nutrients have to
originate at least at 50% from uneaten fish feed, fish solid faeces and fish soluble
242 M. Eck et al.
excretions, thus making the monitoring of the nutrient concentrations available for
plant uptake more difficult. A second drawback is the loss of nutrients through
several pathways such as sludge removal, water renewal or denitrification. Sludge
removal induces a loss of nutrients as several key nutrients such as phosphorus often
precipitate and are then trapped in the evacuated solid sludge. Water renewal, which
has to take place even if in small proportions, also adds to the loss of nutrients from
the aquaponic circuit. Finally, denitrification happens because of the presence of
denitrifying bacteria and conditions favourable to their metabolisms.
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Chapter 10
Aerobic and Anaerobic Treatments
for Aquaponic Sludge Reduction
and Mineralisation
B. Delaide (*)
Developonics asbl, Brussels, Belgium
e-mail: boris@developonics.com; borisdelaide@hotmail.com
H. Monsees
Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany
e-mail: h.monsees@igb-berlin.de
A. Gross
Department of Environmental Hydrology and Microbiology, Zuckerberg Institute for Water
Research, Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev,
Beersheba, Israel
e-mail: amgross@bgu.ac.il
S. Goddek
Mathematical and Statistical Methods (Biometris), Wageningen University, Wageningen,
The Netherlands
e-mail: simon.goddek@wur.nl; simon@goddek.nl
10.1 Introduction
In aquaponics, the wastewater charged with solids (i.e. the sludge) is a valuable
source of nutrients, and appropriate treatments need to be carried out. The treatment
goals differ from conventional wastewater treatment because in aquaponics solids
and water conservation is of interest. Moreover, regardless of the wastewater
treatment applied, its aim should be to reduce solids and at the same time mineralise
its nutrients. In other words, the aim is to obtain a solid-free effluent but rich in
solubilised nutrients (i.e. anions and cations) that can be reinserted into the water
loop in a coupled setup (Fig. 10.1a) or directly into the hydroponic grow beds in a
decoupled setup (Fig. 10.1b). Fish sludge solids are mainly composed of degradable
organic matter so that the solid reduction can be called organic reduction. Indeed, the
complex organic molecules (e.g. proteins, lipids, carbohydrates, etc.) are principally
composed of carbon and will be successively reduced to lower molecular weight
compounds until the ultimate gaseous forms of CO2 and CH4 (in the case of
anaerobic fermentation). During this degradation process, the macronutrients
(i.e. N, P, K, Ca, Mg and S) and micronutrients (i.e. Fe, Mn, Zn, Cu, B and Mo)
that were bound to the organic molecules are released into the water in their ionic
forms. This phenomenon is called nutrient leaching or nutrient mineralisation. It can
be assumed that when high organic reduction is achieved, high nutrient
mineralisation would also be achieved. On the one hand, sludge contains a propor-
tion of undissolved minerals, and on the other hand, some macro- and micronutrients
are released during the mineralisation process. These can quickly precipitate together
and form insoluble minerals. The state between ions and precipitated minerals of
most of the macro- and micronutrients is pH dependent. The most well-known
minerals that precipitate in bioreactors are calcium phosphate, calcium sulphate,
calcium carbonate, pyrite and struvite (Peng et al. 2018; Zhang et al. 2016). Conroy
and Couturier (2010) observed that Ca and P were released in anaerobic reactor
when the pH dropped under 6. They showed that the release corresponded exactly to
the mineralisation of calcium phosphate. Goddek et al. (2018) also observed the
solubilisation of P, Ca and other macronutrients in upflow anaerobic sludge blanket
reactor (UASB) that turned acidic. Jung and Lovitt (2011) reported a 90% nutrient
mobilisation of aquaculture-derived sludge at a very low pH value of 4. In this
condition, all the macro- and micronutrients were solubilised. There is thus an
antagonism between organic reduction and nutrient mineralisation. Indeed, organic
reduction is maximal when the microorganisms are active for degrading the organic
compounds, and this happens at pH in a range of 6–8. Because nutrient leaching
occurs at pH below 6, for optimal organic reduction and nutrient mineralisation, the
most effective would be to divide the process in two steps, i.e. an organic reduction
step at pH close to neutral and a nutrient leaching step under acidic conditions. To
our knowledge, no operation using this two-step approach has been yet reported.
This opens a new field in wastewater treatment and more research for implementa-
tion in aquaponics is needed.
10 Aerobic and Anaerobic Treatments for Aquaponic Sludge Reduction and. . . 251
(a)
Biofilter
Biogas and
Stabilised Sludge
Fish Tank
Water Loop
(b)
Biofilter
Biogas and
Stabilised Sludge
Hydroponic
Beds
RAS
Water Loop
HP
Water Loop
Fig. 10.1 Schematic implementation of sludge treatment in one loop aquaponic system (a) and in
decoupled aquaponic system (b)
The choice of feed is also important in this context. In animal-based feeds where a
major ingredient fraction is still based on animal sources (e.g. fishmeal, bone meal),
bound phosphate, e.g. as apatite (derived from bone meal), is easily available under
acidic conditions, whereas plant-based feeds contain phytate as a major phosphate
source. Phytate in contrast to, e.g. apatite requires enzymatic (phytase) conversion
(Kumar et al. 2012), and so the phosphate is not as easily available.
252 B. Delaide et al.
Aerobic treatment enhances the oxidation of the sludge by supporting its contact
with oxygen. In this case, the oxidation of the organic matter is driven mainly by the
respiration of heterotrophic microorganisms. CO2, the end product of respiration, is
released as is shown in Eq. (10.1).
This process in aerobic reactors is mainly achieved by injecting air into the
sludge–water mixture with air blowers connected to diffusers and propellers. Air
injection also ensures a proper mixing of the sludge.
During this oxidative process, the macro- and micronutrients bound to the organic
matter are released. This process is called aerobic mineralisation. Therefore, further
nutrients can be recycled during the mineralisation process, whereas some nutrients,
e.g. sodium and chloride, can also exceed their threshold for hydroponic application
and must be monitored carefully before application (Rakocy et al. 2007). Aerobic
mineralisation of organic matter, derived from the solid removal unit (e.g. clarifier or
drum filter) in RAS, is an easy way to recycle nutrients for subsequent aquaponic
application.
Moreover, during the aerobic digestion process, the pH drops and promotes the
mineralisation of bound minerals trapped in the sludge. For example, Monsees et al.
(2017) showed that P was released from RAS sludge due to this pH shift. This
decrease in pH is mainly driven by respiration and to a lower extent probably by
nitrification.
Due to a constant supply of oxygen via aeration of the mineralisation chamber
and the abundance of organic matter, heterotrophic microorganisms find ideal
conditions to grow. This results in an increase of respiration and the release of
CO2 that dissolves in water. CO2 forms carbonic acid which dissociates and thereby
lowers the pH of the process water as illustrated in the following equation:
This is at least valid for the starting phase where the pH is still above 6. At a
pH 6, nitrification might significantly slow down or even cease (Ebeling et al.
2006). However, this does not represent a problem for the mineralisation unit.
The general decrease of the pH in the aerobic mineralisation unit in the ongoing
process is the main driver of the release of nutrients present under the form of
precipitated minerals as calcium phosphates. Monsees et al. (2017) noted that around
50% of the phosphate in the sludge was acid soluble, derived from a tilapia RAS
where a standard feed containing fishmeal was applied. Here, around 80% of the
phosphate within the RAS was lost by the cleaning of the decanter and the discarding
of the sludge–water mixture. Considering this fact, the big potential of
mineralisation units for aquaponic applications becomes clears.
The advantages of aerobic mineralisation are the low maintenance with no need
for skilled personnel and no subsequent reoxygenation. The enriched water can be
used directly for plant fertilisation, ideally managed by an online system for the
adequate preparation of the nutrient solution. A disadvantage compared to anaerobic
mineralisation is that no methane is produced (Chen et al. 1997) and, as already
mentioned, the higher energy demand due to the need for constant aeration.
Sieve Plate
pore size: 50-100 µm
Inlet
Outlet
Air Diffuser
Vertical movement of
water-sludge mixture by air bubbles
Fig. 10.2 Schematic example of an aerobic mineralisation unit operated in a batch mode.
Mineralisation chamber (brown) is separated from the outlet chamber (blue) by a sieve plate that
is covered by a solid cover plate during the mineralisation process (strong aeration) to prevent
clogging and formation of fine particles. Organic-rich water from a clarifier or drum filter enters the
mineralisation unit via the inlet. After a mineralisation cycle is completed, nutrient-rich, solid-free
water exits the mineralisation unit via the outlet and is either directly transferred to the hydroponic
unit or kept in a storage tank until needed
254 B. Delaide et al.
10.3.2 Implementation
RAS Hydroponics
Fish Tank
Fish Tank
Fish Tank
Fish Tank
Clarifier Mineralisation
Unit
Biofilter Nutrient
Reservoir
Fig. 10.3 Schematic picture of a decoupled aquaponic system including an aerobic mineralisation
unit. Water can be transferred to the nutrient reservoir either from the RAS water loop or directly
from the mineralisation unit
Anaerobic digestion (AD) has long been used for the stabilisation and reduction of
sludge mass process, mainly because of the simplicity of operation, relatively low
costs and production of biogas as potential energy source. General stoichiometric
representation of anaerobic digestion can be described as follows:
256 B. Delaide et al.
Acetogenesis
Hydrolysis Acidogenesis Methanogenesis
H2
CO2
Formate
Acetate
Organic Monomeric
1 2 3 4 CH4
Matter Compound
Aceton
Butanol
Propannol
Ethanol
Butyrat
Propionate
Lactate
Fig. 10.4 Schematic diagram showing anaerobic degradation of organic matter based on Garcia
et al. (2000)
Effluent
Deflector
Sludge Blanket
Influent
biogas is produced. An inverted cone settler at the top of the digester allows gas–
liquid separation. When the biogas is released from the floc, it is oriented into the
cone by the deflectors to be collected. A slow mixing in the reactor results from the
upwards flow coupled with the natural movement of the microbial flocs that are
attached to biogas bubbles. At some point, the floc leaves the gas bubble and settles
back down allowing for the effluent to be free from TSS, which can then be recycled
258 B. Delaide et al.
back to the system or released. The main advantages of the UASB are the low
operational costs and simplicity of operation while providing high (>92%) solid-
removal efficiency for wastes with low (1–3%) TSS content (Marchaim 1992;
Yogev et al. 2017).
Two recent case studies demonstrated the use of UASB as a treatment for solids in
pilot scale marine and saline RAS, which provide an example of the potential
advantages of this unit in aquaponics (Tal et al. 2009; Yogev et al. 2017). A detailed
look at the carbon balance suggested that about 50% of the introduced carbon (from
feed) was removed by fish assimilation and respiration, 10% was removed by
aerobic biodegradation in the nitrification bioreactor and 10% was removed in the
denitrification reactor (Yogev et al. 2017). Therefore, overall about 25% carbon was
introduced into the UASB reactor of which 12.5% was converted to methane, 7.5%
to CO2 and the rest (~5%) remained as nondegradable carbon in the UASB. In
summary, it was demonstrated that the use of UASB allowed better water
recirculation (>99%), smaller (<8%) production of sludge when compared with
typical RAS that do not have on-site solid treatment, and recovery of energy that
can account for 12% of the overall energy demand of the RAS. It should be noted
that using UASB in aquaponics will also allow significant recovery of up to 50%
more nutrients such as nitrogen, phosphorus and potassium since they are released
into the water as a result of solid biodegradation (Goddek et al. 2018).
The anaerobic membrane bioreactor (AnMBR) is a more advanced technology.
The main process consists of using a special membrane to separate the solids from
the liquid instead of using a decanting process as in UASB. The sludge fermentation
occurs in a simple anaerobic tank and the effluents leave it through the membrane.
Depending on the membrane pore size (going down to 0.1–0.5 μm) even microor-
ganisms can be retained. There are two types of membrane bioreactor design: one
uses a side-stream mode outside the tank, and the other has the membrane unit
submerged into the tank (Fig. 10.6), the latter being more favourable in AnMBR
application due to its more compact configuration and lower energy consumption
(Chang 2014). Membranes of different materials such as ceramic or polymeric
(e.g. polyvinylidene fluoride (PVDF), polyethylene, polyethersulfone (PES), poly-
vinyl chloride (PVC)) may be configured as plate and frame, hollow fibre or tubular
units (Gander et al. 2000; Huang et al. 2010). AnMBR has several significant
advantages over typical biological reactors such as the UASB, namely, decoupling
of (long) sludge retention time (SRT) and (short) hydraulic residence time (HRT),
hence enabling the problem of the AD process’s slow kinetics to be overcome; very
high effluent quality in which most nutrients remain; and removal of pathogens and a
small footprint (Judd and Judd 2008). In addition, efficient biogas production in the
AnMBR can possibly result in a net energy balance.
While this technology deserves a lot of attention and research, it should be noted
that since it is a fairly new technology, there are still several significant drawbacks
that must be addressed before AnMBR would be adopted by the aquaculture
industry. These are the high operational costs due to membrane maintenance to
prevent biofouling, regular membrane exchange and high CO2 fraction (30–50%) in
the biogas which limits its utilisation and contributes to greenhouse gas (GHG)
10 Aerobic and Anaerobic Treatments for Aquaponic Sludge Reduction and. . . 259
(a) (b)
Permeate Permeate
Waste Sludge
Waste Sludge
Bioreactor Bioreactor
Fig. 10.6 (a) Side-stream MBR with a separate filtration unit with the retained fluid recycled back
to the bioreactor; (b) submerged MBR: filtration unit integrated into the bioreactor. (Gander et al.
2000)
emission (Cui et al. 2003). On a positive note, in the near future, new biofouling
prevention techniques will be developed while the membrane cost will certainly drop
with the broader use of this technology. The combination of a UASB with a
membrane reactor to filter the UASB effluent has been successfully studied to
remove organic carbon and nitrogen (An et al. 2009). This combination seems a
promising option for aquaponics for safe and sanitary use of UASB effluents.
10.4.1 Implementation
Biogas Acids
Supernatant Fertilizer
pH ~7 pH ~4
Fig. 10.7 Two-stage anaerobic system. In the first stage (high pH), the carbon will be removed
from the sludge as biogas, whereas the low pH in the second stage allows nutrients that are trapped
in the sludge do dissolve in the water. Usually, volatile fatty acids (VFA) would form in low pH
environments. The removal of the carbon source in the first stage, however, limits VFA production
in such a sequential setup
Organic Waste
Anaerobic Heat and
(e.g. piggeries, Methane
Digestion Electricity
abattoir etc.)
An. Digestion
CO2
Effluent
Extensive
Algal Aquaculture
Animal
Culture Waste Water
Production
Aquaculture
Clean Water
Biomass (Fish, Prawn,
(irrigation etc.)
Pearl etc.)
Bio-Char/ Aquaculture
Animal Feed
Biofertiliser Feed
Fig. 10.8 Anaerobic digestion system integrated with aquaculture and algal culture based on Ayre
et al. (2017)
where ΔS is the sludge inside the reactor at the end of the studied period minus the
one at the beginning of the period, Sout is the total sludge that left the reactor in the
outflow, and Sin is the total sludge that entered the reactor via inflow.
For organic reduction, the sludge (i.e. the term S) can be characterised by the dry
mass of sludge (i.e. TSS) or the mass of oxygen needed to oxidise the sludge
(i.e. COD). Thus, for COD and TSS reduction performances, the smaller the
accumulation and the smaller the quantity in the outflow, the higher the reduction
performance (i.e. high percentage) and so the less solids discharged out of the loop.
Based on the same mass balance, the nutrient mineralisation performance of the
treatment (ζ), i.e. the conversion into soluble ions of the macro- and micronutrients
present in the sludge under undissolved forms, the following formula can be used:
where ζ is the recovery of N nutrient at the end of the studied period in percent,
DNout is the total mass of dissolved nutrient in the outflow, DNin is the total mass of
dissolved nutrient in the inflow and TNin is the total mass of dissolved plus
undissolved nutrients in the inflow.
262 B. Delaide et al.
Thus, similar to the organic reduction performances, the smaller the accumulation
inside the reactor and undissolved nutrient content in the outflow, the higher the
mineralisation performance (i.e. high percentage) and so the dissolved nutrient
recovered in the effluent (or outflow) for aquaponic crop fertilisation (see Example
10.1). The presented mass balance equations are used in the example box.
Example 10.1
The digestion performance of a 250-L anaerobic bioreactor has been evaluated
for an 8-week period. It was fed once a day with 25 L of fresh sludge coming
from a tilapia RAS system, and the equivalent supernatant volume (or output)
was removed from the bioreactor. The fresh sludge (input) had a TSS of 10 g
dry mass (DM) per litre or 1%, and the supernatant (output) had a TSS of
1 gDM/L or 0.1%. The TSS inside the bioreactor at the beginning and at the
end of the period was 20 gDM/L. Consequently, the total DM inputs, outputs
and inside the bioreactor during the evaluated period are calculated as follows:
DM in ¼ 0.01 kg/Ld 25 L 7 days 8 weeks ¼ 14 kg
DM out ¼ 0.001 kg/Ld 25 L 7 days 8 weeks ¼ 1.4 kg
DM to ¼ DM tf ¼ 250 L 0.02 kg/L ¼ 5 kg
The TSS reduction performance (ηTSS) of the bioreactor can then be calculated
as follows:
ηTSS ¼ 100%ð1 ðð5 5Þ þ 1:4Þ=14Þ ¼ 90%
10.6 Conclusions
Fish sludge treatment for reduction and nutrient recovery is in an early phase of
implementation. Further research and improvements are needed and will see the day
with the increased concern of circular economy. Indeed, fish sludge needs to be
considered more as a valuable source instead of a disposable waste.
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Chapter 11
Aquaponics Systems Modelling
Abstract Mathematical models can take very different forms and very different
levels of complexity. A systematic way to postulate, calibrate and validate, as
provided by systems theory, can therefore be very helpful. In this chapter, dynamic
systems modelling of aquaponic (AP) systems, from a systems theoretical perspec-
tive, is considered and demonstrated to each of the subsystems of the AP system,
such as fish tanks, anaerobic digester and hydroponic (HP) greenhouse. It further
shows the links between the subsystems, so that in principle a complete AP systems
model can be built and integrated into daily practice with respect to management and
control of AP systems. The main challenge is to choose an appropriate model
complexity that meets the experimental data for estimation of parameters and states
and allows us to answer questions related to the modelling objective, such as
simulation, experiment design, prediction and control.
11.1 Introduction
In general, mathematical models can take very different forms depending on the
system under study, which may range from social, economic and environmental to
mechanical and electrical systems. Typically, the internal mechanisms of social,
economic or environmental systems are not very well known or understood and
often only small data sets are available, while the prior knowledge of mechanical and
electrical systems is at a high level, and experiments can easily be done. Apart from
this, the model form also strongly depends on the final objective of the modelling
procedure. For instance, a model for process design or simulation should contain
much more detail than a model used for studying different long-term scenarios.
In particular, for a wide range of applications (e.g. Keesman 2011), models are
developed to:
• Obtain or enlarge insight in different phenomena, for example, recovering phys-
ical or economic relationships.
• Analyse process behaviour using simulation tools, for example, process training
of operators or weather forecasts.
• Estimate state variables that cannot be easily measured in real time on the basis of
available measurements, for instance, online process information.
• Control, for instance, in the internal model control or model-based predictive
control concept or to manage processes.
A critical step in the modelling of any system is to find a mathematical model
which adequately describes the actual situation or state. Firstly, the system bound-
aries and the system variables have to be specified. Then relationships between these
variables have to be specified on the basis of prior knowledge, and assumptions
about the uncertainties in the model have to be made. Combining this information
defines the model structure. Still the model may contain some unknown or incom-
pletely known coefficients, the model parameters, which in case of time-varying
behaviour define an additional set of system variables. For a general introduction to
mathematical modelling we refer to, for instance, Sinha and Kuszta (1983), Willems
and Polderman (1998) and Zeigler et al. (2000).
In this chapter, the modelling of an aquaponic (food) production (AP) system will
be described. Figure 11.1 shows a typical example of an AP system, i.e. the so-called
decoupled three-loop aquaponic system. As a result of basic principles modelling,
using conservation laws and constitutive relationships, mathematical models of all
kinds of AP systems are usually represented as a set of ordinary or partial differential
equations. These mathematical models are commonly used for design, estimation
and control. In each of these specific modelling objectives, we distinguish between
analysis and synthesis.
11 Aquaponics Systems Modelling 269
Fig. 11.1 Decoupled, three-loop aquaponic system with RAS, hydroponic and remineralization
subsystems. (Goddek, 2017)
11.2 Background
Many definitions of a system are available, ranging from loose descriptions to strict
mathematical formulations. In what follows, a system is considered to be an object in
which different variables interact at all kinds of time and space scales and that produces
observable signals. These types of systems are also called open systems. A graphical
representation of a general open system (S) with vector-valued input and output signals
is represented in Fig. 11.2. Thus, multiple inputs or outputs are combined in one single
arrow. So, the system variables may be scalars or vectors. In addition, they can be
continuous or discrete functions of time. It is important to stress that the arrows in
Fig. 11.2 represent signal flows and thus not necessarily physical flows.
It is also possible to connect systems into a network, as in an AP system, with parallel,
feedback and feedforward paths. Figure 11.3 presents an example of such a network.
For controller/management analysis and synthesis, it is often convenient to
connect the system (S) to the controller or management strategy (C), as in
Fig. 11.4. Most often the input to the controller or management strategy is the
external steering signal of the controlled system, and the output of the system is
the observed system’s behaviour.
270 K. J. Keesman et al.
S1 S2 ... Sn
S3
Fig. 11.3 Open system network representation
C S
Fig. 11.4 Controlled system
v(.)
w(.)
System: x(.) y(.)
g(.)
state x(.)
u(.)
dxðt Þ
¼ f ðt; xðt Þ; uðt Þ; wðt Þ; pÞ, xð0Þ ¼ x0
dt ð11:1Þ
yðt Þ ¼ gðt; xðt Þ; uðt Þ; pÞ þ vðt Þ, t 2 ℜþ
where the first equation describes the nonlinear and time-varying dynamics of the
system in terms of state variables (x) and the second one expresses the algebraic
relationship between u, x and y. This state-space model representation has been a
starting point for many software implementations for design, control and estimation.
In what follows, however, only deterministic models, thus without the stochastic
vectors v and w, are considered. Let us illustrate this theory on a fish tank system.
Example: Fish Tank System
Consider the following fish tank, which is a typical example of the general system
presented in Fig. 11.7.
Let us start with specifying our prior knowledge of the internal system mecha-
nisms. The following mass balance can be defined in terms of the volume of the
storage tank (V ), also called the state of the system, inflows u(t) and outflows y(t):
dV ðt Þ
¼ uð t Þ y ð t Þ ð11:2Þ
dt
Suppose there is a level controller (LC) that keeps the outflow proportional to the
volume in the tank. This can be enforced by implementing the following propor-
tional control law,
Y ðt Þ ¼ KV ðt Þ ð11:3Þ
with K a real, positive constant. Hence, after substituting Eq. (11.3) into (11.2), we
obtain the following differential equation
dV ðt Þ
þ KV ðt Þ ¼ uðt Þ ð11:4Þ
dt
272 K. J. Keesman et al.
y(t)
For this specific linear differential equation with constant coefficients, an analyt-
ical solution exists and is given by
Z t
yðt Þ ¼ yð0ÞeKt þ KeK ðtsÞ uðsÞds ð11:5Þ
0
under the assumption that u(t) ¼ 0 for t < 0. From this example it is clear that
applying first principles – mass conservation in this case – directly leads to an
ordinary differential equation. In state-space format, the model can be represented as
dxðt Þ
¼ Kxðt Þ þ uðt Þ ð11:6Þ
dt
yðt Þ ¼ Kxðt Þ
With x volume, u flow input and K controller gain. Thus, in terms of the general
state-space Eq. (11.1), f(t, x(t), u(t); p) Kx(t) + u(t) and g(t, x(t), u(t); p) Kx(t).
For two volume-controlled fish tanks in series with volume V1 and V2, and
controller gain K1 and K2, respectively, two mass balances can be formulated, i.e.
dV 1 ðt Þ
¼ K 1 V 1 ðt Þ þ uðt Þ
dt ð11:7Þ
dV 2 ðt Þ
¼ K 1 V 1 ðt Þ K 2 V 2 ðt Þ
dt
K 1 x1 ðt Þ þ uðt Þ
And thus, with x1 ¼ V1,x2 ¼ V2: f ðt; xðt Þ; uðt Þ; pÞ and g
K 1 x1 ð t Þ K 2 x2 ð t Þ
(t, x(t), u(t); p) K2x2(t).
In the next sections, each of the subsystems of the AP system (Fig. 11.1) will be
described in more detail.
Global fish aquaculture reached 50 million tons in 2014 (FAO 2016). Given the
growing human population, there is a growing demand for fish proteins. Sustain-
able growth of aquaculture requires novel (bio)technologies such as recirculating
aquaculture systems (RAS). RAS have a low water consumption (Orellana 2014)
and allow for a recycling of excretory products (Waller et al. 2015). RAS provide
suitable living conditions for fish, as a result of a multistep water treatment, such as
particle separation, nitrification (biofiltration), gas exchange and temperature con-
trol. Dissolved and particulate excretory products can be transferred to secondary
treatment such as plant (Waller et al. 2015) or algae production in integrated aqua-
agriculture (IAAC) systems. IAAC systems are sustainable alternatives to conven-
tional aquaculture systems and in particular are a promising expansion to RAS. In
RAS it would be necessary to circulate the process water which has special
implications for the process technology in both, the RAS and the algae/plant
system. To combine RAS and algae/plant system, a deep understanding of the
interaction between fish and water treatment is prerequisite and can be derived
from dynamic modelling. The metabolism in fish follows a daily pattern which is
well represented by the gastric evacuation rate (Richie et al. 2004). Particle
separation, biofiltration and gas exchange are subjected to the same pattern. For
design purposes the characterization of the basic components of a RAS treatment
system should be investigated through simulation models. These simulation
models are highly complex. Available numerical models for RAS capture only a
small part of the complexity and consider only a part of the components with
corresponding mechanisms. Hence, in this chapter, only a small part of a dynamic
RAS model will be presented, i.e. nitrification-based biofiltration. The conversion
of toxic ammonia into nitrate is a central process in the water treatment process in
RAS. In the following, the dynamic modelling of the mass balance of ammonia
excretion of fish and the conversion of ammonia into nitrate will be demonstrated
as well as the transfer of the nutrient into an aquaponic system. With this it is
possible not only to engineer a RAS but also to integrate fish production into an
IAAC system based on valid parameters.
274 K. J. Keesman et al.
The model is subdivided into a fish model for European seabass, Dicentrarchus
labrax, a model describing the time- dependenting excretion of ammonia, and a
nitrification model (Fig. 11.8). The fish excretion pattern is introduced into the model
through the input vector u (Eq. 11.15), similar to the approach used by Wik et al.
(2009). The complexity of the fish model is kept low to be able to explain its method
of implementation. Nonetheless, a short introduction into modelling fish is presented
in Sect. 11.3.2. Four basic aspects important to describe the nutrient flow in RAS
(Badiola et al. 2012) are:
1. The flow Q, which is the total process water flow per unit time through the RAS,
determines the mass transfer of all dissolved and particulate matter, including
ammonia and nitrate.
2. The excretion of the fish input ammonia to the RAS process water and is depicted
by the product of matrix B and vector u (Eq. 11.15).
3. The ammonia conversion into nitrate, taking place in the nitrification, is depicted
in the nitrification vector n (Eq. 11.15).
4. The nutrient transfer from the RAS to a connected HP system is depicted in vector
u (Eq. 11.15). Other important aspects of the RAS process chain such as solid
removal, dissolved oxygen concentration and carbon dioxide concentration are
not considered here. Hints for modelling these can be found in Sects. 3.1.1 and
3.2.2 of this book.
RAS-System boundary
X NHx-N,excreted
fish excretion
X NO3-N,1 Q X NO3-N,2
X NHx-N,1 X NHx-N,2
Q Exc
hydroponics tank (V1) reactor (V2)
X NHx-N,hydroponics
Fig. 11.8 RAS setup with fish tank, pump, nitrification reactor and water transfer to hydroponic
system
11 Aquaponics Systems Modelling 275
11.3.2 Fish
A variety of models in the scientific literature predict growth and feed intake of
different aquatic species. The models describe growth as weight gain per day, as
percentage growth increment or as specific growth rate based on an exponential
growth model. Models are often valid for specific life stages. Feed consumption,
biomass and gender are influencing the model output as well as the environmental
conditions such as temperature, oxygen level and nutrient concentration (Lugert
et al. 2014). Careful research is needed to identify the correct model used for the
specific application. Commercial RAS that consists of several cohorts of fish in
different life stages require the modelling to incorporate cohorts into the model
(Fig. 8.6) (Halamachi and Simon 2005). The excretory mass flow for the European
seabass (Dicentrarchus labrax) can be estimated with algorithms published by
Lupatsch and Kissil (1998).
Here the net nitrogen mass flow into the process water is estimated from the
feed composition (protein content), the amount of given feed and the nitrogen
retained in body tissues through the growth (weight increment) of fish. The faecal
nitrogen losses are not included in the model, but excretion rate is corrected
assuming a share of 0.25 and 0.75 of nitrogen excretion for faecal loss and
ammonia excretion, respectively. The nitrogen input through the feeding of fish
is estimated from the protein content and the average relative nitrogen content of
proteins which is assumed to be 0.16. The protein content of seabass tissue is
reported at around 0.17 g proteins g1 seabass (Lupatsch et al. 2003). For a fish
gaining body weight by consuming a given amount of feed, the nitrogen excretion
(XN,excreted, g) can be calculated from Eq. (11.9). It is assumed that the feed (Xfeed)
contains 0.5 g protein g1 fish. It is further assumed that the feed conversion rate
equals 1, i.e. 1 g of feed consumption is resulting in 1 g of body weight increase
(Fig. 11.9):
Dissolved ammonia excreted via the gills of fish follows similar daily pattern as
the gastric evacuation rate (GER). GER is described for cold water and warm water
fish by He and Wurtsbaugh (1993) and Richie et al. (2004), respectively. The
excretory pattern can be well simulated with a sine function. The ammonia excretion
can be calculated from Eq. (11.10):
2π
X NHx N , excreted ¼ X N , excreted ½g sin þ1 ð11:10Þ
1440
276 K. J. Keesman et al.
water
biomass [1000g]
protein
feed [1000g]
moisture dissolved
[ TAN, COD phosphor]
lipid
Fig. 11.9 Representation of the mass flows (Sankey chart) of feed ingredients and excretory
products for a fish consuming 1000 g of feed assuming an FCR of 1
11.3.3 RAS
The model as it is described in the following is only valid for the RAS presented in
Fig. 11.8. Other possible process chains for RAS are discussed in Sect. 11.3 of this
chapter. For the mathematical depiction of physical systems, the following assump-
tions were made:
(a) Density of water is assumed to be constant.
(b) Tank and reactor are assumed to be well mixed.
(c) Tank and reactor volume are assumed to be constant.
(d) Process water flow is always greater than zero.
The assumption of a well-mixed tank and reactor leads to a mass balance equation
for continuous stirred-tank reactor (CSTR) as described by Drayer and Howard
(2014) in Eq. (11.11). It must be mentioned that diffusive processes can usually be
neglected in RAS calculations because of a typically high process water flow rate.
For a multi-tank RAS, the following holds:
In the above given equation n represents the number of tanks in the System, x_ i is
the change of concentration of a given substrate x in a volume given by Vi.. The
process water flow into the tank or reactor is represented by Qin. Vi is the volume of
the component where the process water flow Qin is entering in. The process water
flow Qin came from a component having the volume Vj.
The conversion of XNHx-N into XNO3-N in nitrifying biofilters takes place on the
surface area A [m2] available on the bio-carriers in the nitrification reactor (Rusten
2006). The available bioactive surface in the nitrification is calculated by multiplying
the volume of the reactor with the volume-specific active surface of the bio-carriers AS
[m2 m3]. The total bioactive surface is calculated (Eq. 11.12) from the relative filling
fbc of the nitrification reactor which usually is 0.6 (for details, see Rusten 2006).
A ¼ Vnitrification AS f bc ð11:12Þ
The total daily TAN microbial conversion μmax [g d1] (nitrification) was calcu-
lated by multiplying the specific TAN conversion (nitrification) rate, NHxconversion-
2 1
rate [g m d ], with the total active surface area, A [m2], of the bio-carriers. Values
for TAN conversion in different types of nitrifying biofilters can be found in
literature. For moving bed biofilm reactors (MBBR), values are reported by Rusten
(2006). This rate is valid for certain process conditions, and it is assumed that the
bacteria biofilm is fully developed over the whole.
278 K. J. Keesman et al.
The total mass of NHx converted into NO3-N can subsequently be calculated with
a Monod kinetic (Eq. 11.14). For this the NHx-N concentration, XNHx-N,2 [g l1], in
the volume of the nitrification reactor (MBBR) V2, is needed.
d X NHx N,2 1 μ
X NHx N,2 ¼ μmax with Ks ¼ max
dt K
s þ X NHx N,2 V 2
2
ð11:14Þ
d X NHx N,2 1 μmax
X N0s N,2 ¼ þμmax with Ks ¼
dt K s þ X NHx N,2 V2 2
Given Eqs. (11.9, 11.10, 11.11, 11.12, 11.13 and 11.14), the following state-
space model (combining fish-nitrification) results
dxðt Þ
¼ A X þ B u þ n
dt 2 3
2 3 2 3 0
X NHx N,1 X NHx N, excreted 6 μmax ½X 2 1 7
6 X NHx N,2 7 6 7 6 7
0 7 n¼6 K s þ ½X 2 V 2 7
X¼64 X NO3 N,1 5
7 u¼6
4 QExc X NHx N, hydroponics 5
6 7
6 0 7
4 μmax ½X 2 1 5
X NO3 N,2 0 þ
2 3 K s þ ½X 2 V 2
Q QExc Q
0 0
6 V1 V1 V1 7
6 7
6 Q Q 7
6 0 0 7
6 V V 7
A¼6 2 2
Q 7
6 Q QExc
7
6 0 0 7
6 V1 V1 V1 7
4 Q Q5
0 0
2 3 V2 V1
1
0 0 0
6 V1 7
6 7
6 1 7
6 0 0 0 7
6 V 7
B ¼ 6 2
7
6 0 1
0 7
6 0 7
6 V1 7
4 1 5
0 0 0
V2
ð11:15Þ
11 Aquaponics Systems Modelling 279
Example
In this example, a theoretical RAS with V_reactor ¼ 1300 l and
V_tank ¼ 6000 l is simulated.
All simulations had a daily feed input of 2000 g/day with 500 g protein/kg
feed (Eq. 11.8). The daily TAN excretion was assumed to be a sine curve
(Eq. 11.9). Active surface of the bio-carriers AS is 300 [m2 m3], and the
relative filling of the reactor fbc is 0.6. Specific TAN conversion rate,
NHxconversion-rate, is 1.2 [g m2 d], and the biofilm is supposed to be fully
developed (Eqs. 11.11 and 11.12). The state-space representation (Eq. 11.14)
was implemented in MATLAB Simulink. The Example showcases the impor-
tance of mass flow for nutrient concentrations in coupled systems (Fig. 11.10
and 11.11).
Anaerobic digestion (AD) of organic material is a process that involves the sequential
steps of hydrolysis, acidogenesis, acetogenesis and methanogenesis (Batstone et al.
2002). The anaerobic digestion of a mixture of proteins, carbohydrates and lipids is
visualized in Figure 11.11. Most often, hydrolysis is considered as the rate-limiting
step in the anaerobic digestion of complex organic matter (Pavlostathis and Giraldo-
Gomez 1991). Thus, increasing the hydrolysis reaction rate will most likely lead to a
Fig. 11.10 Simulation of TAN (XNHx-N,1) in [mg/l] over 2 days ¼ 2880 min with Q ¼ 300 l/min
(blue) and Q ¼ 200 l/min (orange)
Fig. 11.11 Simulation of nitrate-N (XNO3-N,1) in [mg/l] over 50 days ¼ 72,000 min with
QExc ¼ 300 l/day (yellow), QExc ¼ 480 l/day (orange) and QExc ¼ 600 l/day (blue)
280 K. J. Keesman et al.
higher anaerobic digestion reaction rate. However, increasing the reaction rates needs
further understanding of the related process. Further understanding can be obtained via
experimentation and/or mathematical modelling. As there are many factors influenc-
ing, for instance, the hydrolysis process, such as ammonia concentration; temperature;
substrate composition; particle size; pH; intermediates; degree of hydrolysis; i.e. the
potential of hydrolysable content; and residence time, it is almost impossible to
evaluate the total effect of the factors on the hydrolysis reaction rate through exper-
imentation. Mathematical modelling could therefore be an alternative, but as a result of
all the uncertainties in model formulation, rate coefficients and initial conditions, no
unique answers can be expected. But, a mathematical modelling framework would
allow sensitivity and uncertainty analyses to facilitate the modelling process. As
mentioned before, hydrolysis is just one of the steps in anaerobic digestion. Conse-
quently, understanding and optimization of the full anaerobic digestion process needs
connections from hydrolysis to the other processes taking place during anaerobic
digestion and interactions between all these steps.
The well-known and widely used ADM1 (anaerobic digestion model #1) is a
structured model including disintegration and hydrolysis, acidogenesis, acetogenesis
and methanogenesis steps. Disintegration and hydrolysis are two extracellular steps.
In the disintegration step, composite particulate substrates are converted into inert
material, particulate carbohydrates, protein and lipids. Subsequently, the enzymatic
hydrolysis step decomposes particulate carbohydrates, protein and lipids to mono-
saccharides, amino acids and long-chain fatty acids (LCFA), respectively (Batstone
et al. 2002) (see Fig. 11.12).
ADM1 is a mathematical model that describes the biological processes and
physicochemical processes of anaerobic digestion as a set of differential and alge-
braic equations (DAE). The model contains 26 dynamic state variables in terms of
concentrations, 19 biochemical kinetic processes, 3 gas-liquid transfer kinetic pro-
cesses and 8 implicit algebraic variables for each process unit. As an alternative, Galí
et al. (2009) described the anaerobic process as a set of differential equations with
32 dynamic state variables in terms of concentrations and an additional 6 acid-base
kinetic processes per process unit. For an overview of the modelling of anaerobic
digestion processes, we refer to Ficara et al. (2012). However, in what follows and
for some first insights into the AD process, we will present a simple nutrient-balance
model of AD in a sequencing batch reactor (SBR).
The nutrient mineralization can be calculated using the following equation (Delaide
et al. 2018):
DNout DNin
NR ¼ 100% ð11:15aÞ
TNin DNin
11 Aquaponics Systems Modelling 281
Hydrolysis
Acidogenesis
Acetogenesis
Methanogenesis
CH4, CO2
Fig. 11.12 A simplified scheme for the anaerobic digestion of complex particulate organic matter.
(based on El-Mashad 2003)
where NR is the nutrient recovery at the end of the experiment in percent, DNout is
the total mass of dissolved nutrient in the outflow, DNin is the total mass of dissolved
nutrient in the inflow and TNin is the total mass of dissolved plus undissolved
nutrients in the inflow (see also Fig. 11.13).
The organic reduction performance of the reactor can be calculated using the
following equation:
ΔOM þ T OM out
ηOM ¼ 1 ð11:15bÞ
T OM in
where ΔOM is the organic matter (i.e. COD, TS, TSS, etc.) inside the reactor at the
end of the experiment minus the one at the beginning of the experiment, TOM out is
the total OM outflow and TOM in is the total OM inflow (see also Fig. 11.14).
282 K. J. Keesman et al.
The crop water use and nutrient uptake is a central subsystem of aquaponics. The HP
part is complex, as pure uptake of water and dissolved nutrients do not simply follow
a rather simple linear relationship as, e.g. fish growth. To create a full-functional
model, a complete greenhouse simulator is needed. This involves sub-model systems
of greenhouse physics including climate controllers and crop biology covering
interactive processes with biological and physical stressors.
However, from the HP point of view, greenhouse climate is the main driver for
the complete aquaponic system, including, next to the nutrient balances, feedback
loops of heat produced by the fish and additional CO2 supplied to the plants as
reported by Körner et al. (2017) (Fig. 11.15).
In this model, the fish culture produces heat through metabolic processes. The
amount of heat produced by the fish is directly calculated from oxygen consumption
that is a function of temperature and a constant for heat production for one unit
oxygen consumed (i.e. 13608 J g1 fish). Heat from breakdown of organic matter
(Qbio), e.g. faeces and feed remain, is also contributing to the heat balance. Energy
supply to the water system can then be calculated by heat production through the fish
calculated from an average oxygen consumption rate (fO2,Twb). Additional heat
production can then be calculated by biological breakdown of faeces (Fig. 11.16).
CO2 production from the aquatic subsystem (dCO2 , g h1 ), i.e. delivery to the aerial
environment (d, g h1), can be calculated for the given water temperature (TH2O, K)
from oxygen delivery to the system ( d O2 , g h1) at water base temperature (TH2O,b, K)
and the Q10 value of fish respiration (Q10,R). The following relationships are used:
11 Aquaponics Systems Modelling 283
GH Climate
Microclimate
TC , ETC
HP Fish
Heat Demand
Heat Energy
with feed amount for the fish (ffish, g h1), oxygen consumption rate at base
temperature (fO2, kg [O2] kg1 [feed]), fraction of feed loss wO2 () and mass
balance of O2/CO2 ().
To calculate the basis of aquaponics, i.e. the process flow (indicated with arrows,
!) greenhouse macroclimate ! microclimate ! evapotranspiration ! nutrients
uptake, various greenhouse simulators that were developed in the past can be used
and combined with aquaculture to an aquaponic system. All greenhouse models
include a crop growth model. The model quality, however, can vary a lot from
simple empirical regression models, e.g. Boote and Jones (1987), via deterministic
models, e.g. Heuvelink (1996), to functional structural plant models (FSPM),
e.g. Buck-Sorlin et al. (2011). As current crop growth and development models
are inaccurate and have limited predictive power (Poorter et al. 2013), models are
occasionally employed in crop management, but then mainly for planning issues in
greenhouse simulators, e.g. Vanthoor (2011) and Körner and Hansen (2011). Pre-
diction accuracy is jeopardized by many sources of uncertainty, such as modelling
284 K. J. Keesman et al.
Fig. 11.16 Aquaculture system implemented in the greenhouse with humidity, temperature and
CO2 concentrations of the air (RHair Tair, CO2,air), heat from (Q) fish environment (fish), biological
breakdown (bio) and heat fluxes (ɸ), taken from Körner et al. (2017)
with greenhouse air temperature (Ta, K), vapour pressure air density (ρa, g m2),
Stefan-Boltzmann constant (σ, Wm2 K4), specific heat capacity of the air (cp, J
g1 K1), the psychrometric constant (γ, Pa K1) and the slope between saturated
vapour pressure and greenhouse air temperature (δ, Pa K1).
Leaf temperature is the central part of the microclimate model, it has feedback
loops to several input variables and especially stomata resistance (often also used as
its reciprocal, the conductance), and the calculation needs several simulation steps
for equilibrium. For HP, as part of the aquaponic system, however, modelling water
and nutrient fluxes is most important. All water and nutrient balances in a closed
multi-loop system are controlled based on the evapotranspiration rate of the crop ETc
(Chap. 8). Commonly ETc is calculated as latent heat of evaporation, i.e. in energy
terms (λE, Wm2), and can be in accordance to leaf temperature expressed in
different canopy layers z
0 1
δ ρa cp
γRn, a ðzÞ þ þ ρ c =4σT VPDs ðzÞ
1 1
γ r b ð zÞ 3
λE ðzÞ ¼ @ a p A ð11:18Þ
a
1 þ δγ þ rrbs ððzzÞÞ þ ρ c 1
3 ð r s ð zÞ þ r b ð zÞ Þ
a p =4σT a
Disturbances
Outside Temperature
Heat Aquasystem
Outside Humidity
CO2 Aquasystem
Solar Radiation
Outside Wind
(Indoor Conditions)
CO2 Temperature
(Control Actions)
Heat Greenhouse RH
Climate
Output
Input
Equation (11.18), however, only calculates the water flux through the crop, while
the easiest way to estimate nutrient uptake is the assumption that nutrients are taken
up/absorbed as dissolved in irrigation water and assuming that no element specific
chemical, biological or physical resistances exist. In reality uptake of nutrients is a
highly complicated matter. Consequently, to maintain equilibrium, all nutrients
taken up by the crop as contained in the nutrient solution need to be added back to
the hydroponics system (see Chap. 8). However, Eq. (11.18) only calculates the
potential ETc, while too high potential levels can result in a higher transpiration than
plants can handle, and then potential water loss may exceed water uptake. For that,
the simple assumption of nutrient uptake is not satisfying. As described in Chap. 10,
the different nutrients can have different states and change states with, e.g. pH, while
the plant availability strongly depends on pH and the relation of nutrients to each
other. In addition, the microbiome in the root zone plays an important role, which is
not implemented in models yet. Some models, however, differentiate between
phloem and xylem pathways. The vast amount of nutrients, however, is not modelled
in detail for aquaponics nutrient balancing and sizing of systems, while the easiest
way to estimate nutrient uptake is the assumption that nutrients are taken
up/absorbed as dissolved in irrigation water and apply the above explained ETc
calculation approach.
For control purposes the greenhouse is typically considered as a black box, where
outside climate conditions determine the disturbance inputs, CO2 supply, heating
and ventilation are the control inputs, and the greenhouse macro- and microclimate
define the output of the system (Fig. 11.17).
11 Aquaponics Systems Modelling 287
To control the greenhouse, the actions are directed to minimize the fast impacts of
the disturbances, i.e. being ahead of expected changes by smart control. For that,
control actions such as feedback and feedforward are used (Chap. 8). The best
control, however, can be achieved when using a complete greenhouse model and
combine it with weather forecast (Körner and Van Straten, 2008) attaining a model-
based optimal greenhouse climate control, as worked out by Van Ooteghem (2007).
In aquaponics, flow charts or stock and flow diagrams (SFD) and causal loop
diagrams (CLDs) are commonly used to illustrate the functionality of the aquaponic
system. In the following, flow chart and CLDs will be described.
To get a systemic understanding of the aquaponics, flow charts with the most
important components of the aquaponics are a good tool to show how material
flows in the system. This can help, for example, in finding missing components and
unbalanced flows and mainly influencing determinants of the subprocesses. Fig-
ure 11.18 shows a simple flow chart in aquaponics. In the flow chart, fish food and
water are added to the fish tank, where the feed is taken by the fish for growth, the
water is enriched with the fish waste and the nutrient-enriched water is added to the
hydroponics system to produce plant biomass. From the flow chart, a CLD shown in
Fig. 11.19 can be easily constructed.
Fish
Waste
Sediment
Fig. 11.18 Example of a flow chart in aquaponics (only RAS and HP exchange)
11 Aquaponics Systems Modelling 289
+
Nutrients
Fish Feed Input Concentration -
+
R B
+
Plant Biomass Nutrients Uptake
+ Fish Biomass +
Fig. 11.19 Causal loop diagram (CLD) illustrating examples of a reinforcing and a balanced loop
within aquaponic systems. The reinforcing loop (R) is one in which an action produces a result
which influences more of the same action and consequently resulting in growth or decline, where as
a balancing loop (B) attempts to bring things to a desired state and keep them there (e.g. temperature
regulation in the house)
Causal loop diagrams (CLDs) are a tool to show the feedback structure of a system
(Sterman 2000). These diagrams can create a foundation for understanding complex
systems by visualizing the interconnection of different variables within a system.
When drawing a CLD, variables are pictured as nodes. These nodes are connected by
edges, which form a connection between two variables accordingly. Figure 11.19
shows that such edges can be marked as either positive or negative. This depends on
the relation of the variables to one another. When both variables change into the
same direction, then one can speak of a positive causal link. A negative causal link
thus causes a change in opposite directions. When connecting two nodes from both
sides, one creates a closed cycle that can have two characteristics: (1) a reinforcing
loop that describes a causal relationship, creating exponential growth or collapse
within the loop or (2) a balancing loop in which the causal influences keep the
system in an equilibrium. Figure 11.19 shows an example of both types of loops.
Let us illustrate this (Fig. 11.20) for the flow chart of Fig. 11.18.
It is obvious that CLD and SFD are very useful for system understanding, when
the model does not require numerical accuracy. If numerical accuracy is required, the
process should be studied further with a system dynamic tool diagram (SDTD) and
modelled in dynamic system simulation software. For example, the CLD in
Fig. 11.20 can be augmented with differential equations to a SDTD (Fig. 11.21).
290 K. J. Keesman et al.
Fish Feed
Input
+
Fish Biomass Plant Biomass
+
- -
+
Fish Tanks: Hydroponics:
Nutrients Out
Nutrients in Water Nutrients in Water
+ +
+ +
Nutrients Nutrients
Concentration Concentration
- -
- -
Fish Tanks: Hydroponics:
Water Out
Water Volume Water Volume
+
+ +
Water Input
From the SDTD, we can now see how the differential equations for the nutrients
balance in the tank look like. We know that the nutrient flow out of the fish tank
(Mxfout) must be the water flow (Qfout) times the concentration in the out stream (Cxf):
M xfout ¼¼ C xf Qfout
Assuming a stirred tank gives the nutrient concentration of the fink tank to:
C xf ¼ M xf =V f
Mfeed
+
Mxfin Mplant
+
- -
+
Mxf Mxfout Mxh
+ +
+ +
Cxf = Mx / Vf Cxh = Mxh / Vh
- -
- -
Vf Qfout Vh
+
+ +
Qfin
11.7.3 Software
In addition to basic computer languages, such as Fortran, C++ and Python, for fast
computation and fully user-specific implementation, all kinds of advanced software
tools are available. These advanced software tools offer a variety of environments,
concepts and options. We can model state variables, differential equations, connec-
tions and loops. In addition, we can use the model for simulations, stability analysis,
optimization and control.
292 K. J. Keesman et al.
The main reasons for modelling of a system are to understand and control
it. Therefore, the model helps to predict the system dynamics or behaviour. The software
applications could allow us to do three consequent tasks: (a) the modelling itself, (b) the
simulations of the model(s) and (c) optimization of the model and/or simulation.
Mathematica software is for functional analysis of mathematically described
problems (Wolfram 1991). The concept is based on the LISP approach (McCarthy
and Levin 1965.), a very effective functional programming language. The syntax is
reasonably simple, and this software is popular in mathematics, physics and systems
biology. Especially, the Ndsolve module helps to solve ordinary differential equa-
tions, plot the solution and find specific values.
Very similar tools for solving ODEs are offered by the Maple. This software is
very powerful; between its features belong boundary problems solution, exact
solutions and mathematical approximations. Copasi (complex pathway simulator)
is a software tool for simulation and analysis of biochemical networks via ordinary
differential equations.
SageMath is a free open-source mathematics software system. The software is
Python-based and facilitates the simulation of ODE models. Data2Dynamics soft-
ware is a collection of numerical methods for quantitative dynamic modelling and is
a comprehensive model and data description language. The software allows the
analysis of noise, calibration and uncertainty predictions and has libraries of biolog-
ical models.
Probably the best simulation language is Simula (probably not in use anymore)
and Simula 67, considered at the beginning as a package for Algol 60. These were
the first fully object-oriented languages, introducing classes, inheritance, subclasses,
garbage collector and others. In the beginning of the twenty-first century, the creators
Ole-Johan Dahl and Kristen Nygaard were awarded the IEEE John von Neumann
Medal and the A. M. Turing Award (Dahl and Nygaard 1966).
The idea behind Simula was that objects have life; they start to exist, do their
being and cease. The objects are defined as general classes (template code), and each
instance of such object has a ‘life’ in the simulation. The language was quite difficult
to learn. However, it offered the possibility to model processes object by object and
run simulation of their lives. The simulation runs on the basis of discrete events, and
it is possible to simulate objects in co-routine. More tasks can start, run, detach,
resume and complete in overlapping time periods in quasiparallel processes. Today’s
hardware allows us modelling and simulation in fully parallel threads. However,
many of the Simula concepts were already used for development of other languages,
namely, Java, C/C++/C# and persistent objects libraries like DOL (Soukup and
Machacek 2014). Current successor of Simula is BETA, extending and featuring
the possibilities of inheritance in concepts of nested (sub)classes (with nested local
time) and patterns (Madsen et al. 1993).
It is always an option to use any of the object-oriented languages and specific
libraries and program all the necessary code for a specific model. On the other hand,
already existing graphical programming environments allow to design and link the
structure of the modelled system from libraries of objects (signal generator, sum,
integrator, etc.), parametrize them and run the simulation in virtual time.
11 Aquaponics Systems Modelling 293
Aquaponics are complex technical and biological systems. For example, possible
explanations for fish not growing properly can be small food rations, adverse water
quality, technical problems causing stress, etc. Due to the inherently slow biology,
scientific investigations of the validity of these explanations would be tedious and
require several experimental trials to get all important factors and their interactions,
demanding a lot of facilities, expertise, research time and financial assets. Therefore,
the issue of modelling aquaponic systems was addressed in this chapter. In
aquaponics, modelling is required for different objectives: (i) insight/understanding,
(ii) analysis, (iii) estimation and (iv) management and control. For all these objec-
tives, appropriate models are required. For example, to achieve objectives (ii) and
(iii), an empirical approach can be utilized which uses statistical models to analyse
data from previous experimental trials with the objective of extracting as much
information as possible without conducting new experiments. Statistical models
can reveal the most important factors affecting fish and crop production in the
aquaponic systems. Future experiments could concentrate on these factors, thus
making the utilization of costly research assets more effective.
The complexity of aquaponic systems, due to their feedback character and the
interactions between RAS and hydroponic system, water treatment and fish growth,
implies that in order to fulfil objectives (i) and (iv), i.e. to understand or optimize a
plant (configuration, size, fish, feed, flows, etc.) with respect to cost, stability,
robustness and water quality, non-trivial theoretical models of most of the system
components described in this chapter are required. The advantage of these theoretical
models presented over statistical models is their stronger ability to analyse the
11 Aquaponics Systems Modelling 295
process underlying the aquaponics and the possibility to model the time aspect
(dynamics). Statistical models just confirm or refute a hypothesis and to what extent
variables covary but give no evidence of the underlying processes. On the other
hand, theoretical models allow us to simulate the processes according to a hypoth-
esis, compare simulated with observed data, evaluate both the hypothesis and the
model and make adaptions. The validity of statistical models may not be beyond the
operational range they were trained for, whereas theoretical models can be defined
and used for a wide range of environments, provided that the models are validated
for these ranges before application. For example, the multiple regression model used
to assess relationships between fish growth with Oreochromis niloticus as fish
species and environmental variables in an aquaponics facility in Germany cannot
be easily applied to Spain with Cyprinus carpio, whereas a theoretical model
describing the underlying processes (e.g. fish behaviour, aquaculture, freshwater
ecology) as mathematical equations can be adjusted relatively easily because the fish
and ecological process underlying that model are basically the same for the two sites.
Nevertheless, theoretical models also require some parameters such as reaction
constants and substance settling velocity in settling tank to be determined. This is
achieved commonly based on empirical study of one facility or very few facilities or
in most cases from previously published studies (secondary sources). Studies based
on secondary sources have limitations imposed by the given structure and amount of
the available data, which is not existent when the data come from an experimental
setup designed ad hoc for the study. However, estimating model parameters using
experimental data from one aquaponics facility only can have problems regarding
generalizability and replication of the results due to particular conditions present in
the study. The data scarcity sometimes imposes strong restrictions to models that
limit their practicality. The development of studies for parameter estimation with
primary data that use a larger number of aquaponics facilities than earlier studies
does help to overcome the present limitations and provide better and reliable results.
This, however, is not an easy challenge for aquaponics researchers.
Simulation of aquaponics with the mathematical models under a wide range of
management conditions will improve the understanding of aquaponics, verify dif-
ferent aquaponics configurations and point the way to the most promising strategies
for improving aquaponics facilities. Again, this can lead to a more efficient way of
conducting experiments.
Some modelling tools were also presented in this chapter. Traditionally, stock and
flow diagrams (SFD) have been used for understanding processes as support tools
for quantitative analysis. They are used to comprehend the flow and fluxes of
quantities but lack the ability to illustrate the information associated to the flow
and fluxes. Causal loop diagram (CLD) can be used to transfer complex SFD system
into understandable simplified feedback structures. Together, the SFDs and the
CLDs fully define the differential equation system. If only a simple qualitative
understanding of the system is required, then CLD and SFD may be enough, but if
the answer requires a numerical accuracy, then the problem can be investigated
further with system dynamic tool diagrams (SDTD) and subsequently be modelled
in a software tool for numerical simulation.
296 K. J. Keesman et al.
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Chapter 12
Aquaponics: Alternative Types
and Approaches
B. Kotzen (*)
School of Design, University of Greenwich, London, UK
e-mail: b.kotzen@greenwich.ac.uk
M. G. C. Emerenciano
Santa Catarina State University (UDESC), Aquaculture Laboratory (LAQ), Laguna, SC, Brazil
CSIRO Agriculture and Food, Aquaculture Program, Bribie Island Research Centre, Bribie
Island, QLD, Woorim, Australia
e-mail: mauricio.emerenciano@csiro.au
N. Moheimani
Algae R&D Centre Director, School of Veterinary and Life Sciences, Murdoch University,
Murdoch, WA, Australia
e-mail: n.moheimani@murdoch.edu.au
G. M. Burnell
School of Biological, Earth and Environmental Sciences, University College Cork, Cork,
Ireland
e-mail: g.burnell@ucc.ie
12.1 Introduction
This chapter discusses a number of key allied and alternative technologies that either
expand or have the potential to expand the functionality/productivity of aquaponic
systems or are associated/stand-alone technologies that can be linked to aquaponics.
The creation and development of these systems have at their core the ability,
amongst other things, to increase production, reduce waste and energy and in most
cases reduce water usage. Unlike aquaponics, which may be seen to be in a
mid/teenage stage of development, the novel approaches discussed below are in
their infancy. This, however, does not mean that they are not technologies valuable
in their own right and have the potential to deliver future food, efficiently and
sustainably. The methods discussed below include aeroponics, aeroaquaponics,
algaeponics, biofloc technology for aquaponics, maraponics and haloponics and
vertical aquaponics.
12.2 Aeroponics
12.2.1 Background
Aeroponic systems thus function by spraying or misting the root zone area with
nutrient solution. The roots of the plants are thus suspended in air and are subjected
to a continuous or intermittent/periodic spray/misting of nutrient-rich water droplets,
in the form of droplets or very fine mists, with droplet sizes from 5 to 50 μm
(microns). It is usual to find ‘hobby/domestic’ kit with spray droplet sizes of
30–80 μm. Ultrasonic or dry-fog atomizers produce a droplet size <5 μm, but
these require compressed air and very fine nozzles, or it may be possible to use
ultrasonic transducers to produce these mists.
In aeroponics, as with hydroponics, nutrient supply can be optimized and in a
comparison between hydroponics and aeroponics, Hikosaka et al. (2014) note that
no difference was found between growth and harvest quality in lettuce using dry-fog
aeroponics. However, there was a significant increase in root respiration rates and
photosynthesis rates of leaves. They also note that this system also uses less water
and that it can be more efficient and easier to manage than conventional hydroponics
(Hikosaka et al. 2014). In a review paper on modern plant cultivation technologies in
agriculture under controlled environments, Lakhiar et al. (2018) note that aeroponics
‘is considered the best plant growing method for food security and sustainable
development’.
Clawson et al. (2000) report the tests by Tibbits et al. (1994) that continuous misting
can ‘contribute to fungal and bacterial growth in the vicinity of or on the plants’, and
furthermore some researchers have found that due to fine droplets and with
continuous fogging systems, there can be difficulties ‘in delivering nutrients to all
304 B. Kotzen et al.
the plants where there is a high density of plants’. In this respect it has been shown
that misting at intervals delivers a healthier system and healthier roots compared to
continuous fogging and hydroponic techniques. Using intervals also makes the
plants more resistant to any interruptions in misting, conditioning the plants to thrive
longer on lower moisture levels, with a likely reduction in pathogen levels. For
effective misting, ‘droplet size and velocity are also important aeroponic parameters.
The root’s mist collection efficiency depends on its filament size, drop size, and
velocity’ (Clawson et al. 2000).
12.3 Algaeponics
12.3.1 Background
Microalgae are unicellular photoautotrophs (ranging from 0.2 μm up to 100 μm) and
are classified in various taxonomic groups. Microalgae can be found in most
environments but are mostly found in aquatic environments. Phytoplankton are
responsible for over 45% of world’s primary production as well as generating over
50% of atmospheric O2. In general, there is no major difference in photosynthesis of
microalgae and higher plants (Deppeler et al. 2018). However, due to their smaller
size and the reduction in a number of internally competitive physiological organ-
elles, microalgae can grow much faster than higher plants (Moheimani et al. 2015).
Microalgae can also grow under limited nutrient conditions and have the ability to
adapt to a wider range of environmental conditions (Gordon and Polle 2007). Most
importantly, microalgal culture does not compete with food crop production regard-
ing arable land and freshwater (Moheimani et al. 2015). Furthermore, microalgae
12 Aquaponics: Alternative Types and Approaches 305
can efficiently utilize inorganic nutrients from waste effluents (Ayre et al. 2017). In
general, microalgal biomass contains up to 50% carbon making them a perfect
candidate for bioremediating atmospheric CO2 (Moheimani et al. 2012).
The increase in extensive worldwide agriculture and animal farming has resulted
in significant increases in biologically available nitrogen and phosphorus entering
the terrestrial biosphere (Galloway et al. 2004). Crop and animal farming and sewage
systems contribute significant amounts to these nutrient loads (Schoumans et al.
2014). The infiltration of these nutrients into water streams can cause massive
environmental issues such as harmful algal blooms and mass fish mortality. For
instance, in the USA, nutrient pollution from agriculture is acknowledged as one of
the major sources of eutrophication (Sharpley et al. 2008). Controlling the flow of
nutrients from farming operations into the surrounding environment results in both
technical and economic challenges that must be overcome to reduce such effects.
There have been various successful processes developed to treat waste effluent with
high organic loads. However, almost all of these methods are not very effective in
removing inorganic elements from water. Furthermore, some of these methods are
rather expensive to operate. One simple method for treating organic waste is
anaerobic digestion (AD). The AD process is well understood and when operated
efficiently, it can convert over 90% of the wastewater organic matters to bio-methane
and CO2 (Parkin and Owen 1986). The methane can be used to generate electricity
and the generated heat can be used for various additional purposes. However, the AD
process results in creating an anaerobic digestion effluent (ADE) which is very rich
in inorganic phosphate and nitrogen as well as high COD (carbon oxygen demand).
In certain locations, this effluent can be treated using microalgae and macroalgae
(Ayre et al. 2017).
A number of inhibitory physical, chemical and biological factors can inhibit high
microalgal production. These are described in Table 12.1.
A basic knowledge of the critical growth limitations is probably the most
essential factor before applying any microalgae to any process. Light is by far
the most important limiting factor affecting the growth of any alga. Temperature is
also a critical factor for mass algal production (Moheimani and Parlevliet 2013).
However, these variables are difficult to control (Moheimani and Parlevliet 2013).
Next to light and temperature, nutrients are the most important limiting factor
affecting the growth of any alga (Moheimani and Borowitzka 2007) and each
microalgal species tends to have its own optimum nutrient requirements. The most
important nutrients are nitrogen, phosphorus and carbon (Oswald 1988). Most
308 B. Kotzen et al.
Organic Waste
Anaerobic Heat and
(e.g. piggeries, Methane
Digestion Electricity
abattoir etc.)
An. Digestion
CO2
Effluent
Extensive
Algal Aquaculture
Animal
Culture Waste Water
Production
Aquaculture
Clean Water
Biomass (Fish, Prawn,
(irrigation etc.)
Pearl etc.)
Bio-Char/ Aquaculture
Animal Feed
Biofertiliser Feed
Fig. 12.1 Integrated process system to use algal culture for treating organic waste and potential end
users. (The process is designed based on information from Ayre et al. 2017 and Moheimani et al.
2018)
may attract insects, reduce water quality and when decomposing can deplete oxygen.
However, an experiment by Addy et al. (2017) shows that algae can improve water
quality in an aquaponic system, help control pH drops related to the nitrification
process, generate dissolved oxygen in the system, ‘produce polyunsaturated fatty
acids as a value-added fish feed and add diversity and improve resilience to the
system’. One of the ‘holy grails’ of aquaponics is to produce at least part of the food
that is fed to the fish as part of the system and it is here that research is required in
producing algae that could be grown with part of the aquaponics water, most
probably in a separate loop, which can then be fed as part of the diet to the fish.
increasing in many parts of the world (Turcios and Papenbrock 2014). This has led to
an increased interest and/or move towards alternative water sources (e.g. brackish to
highly saline water as well as seawater) and the use of euryhaline or saltwater fish,
halophytic plants, seaweed and low salt-tolerant glycophytes (Joesting et al. 2016). It
is interesting to note that whilst the amount of saline in underground water is only
estimated as 0.93% of world’s total water resources at 12,870,000 km3, this is more
than the underground freshwater reserves (10,530,000 km3) which makes up 30.1%
of all freshwater reserves (Appelbaum and Kotzen 2016).
The use of saline water in aquaponics is a relatively new development and as with
most new developments the terms used to describe the range/hierarchy of types
needs to be established on a firm footing. In its short history, the term maraponics
(i.e. marine aquaponics) has been coined for seawater aquaponics (SA), in other
words, systems that use seawater as well as brackish water (Gunning et al. 2016).
These systems are mainly located on-land, in coastal locations and in the case of SA,
close to a seawater source. But there are fish as well as plants that grow and can be
used in aquaponic units where water salinity levels vary. Thus whilst it makes
etymological sense to use the term ‘maraponics’ for seawater aquaponics, it makes
less sense to term brackish water aquaponics using this term. We thus suggest that a
new term needs to be added to the aquaponic lexicon and this is ‘haloponics’,
deriving from the Latin word halo meaning salt and combining this with suffix
ponics. Thus maraponics is an on-land integrated multitrophic aquaculture (IMTA)
system combining the aquacultural production of marine fish, marine crustaceans,
marine molluscs, etc. with the hydroponic production of marine aquatic plants
(e.g. marine seaweeds, marine algae and seawater halophytes) using oceanic strength
seawater (approximately 35,000 ppm [35 g/L]). However aquaponic systems utiliz-
ing saline water below oceanic levels in a range of salinities should be termed
haloponics (slightly saline water –1000 to 3000 ppm [1–3 g/L], moderately saline
3000–10,000 ppm [3–10 g/L] and high salinity 10,000–35,000 ppm [10–35 g/L]).
These systems are also on-land IMTA systems combining aquacultural production
with the hydroponic production of aquatic plants, but both the fish and plants are
adapted to or grow well in what may be termed brackish water.
Although the concept of maraponics is very new, an interest in on-land seaweed-
based integrated mariculture began to appear in the 1970s, starting from a
laboratory-scale and then expanding to outdoor pilot-scale trials. In some of the
earliest experimental studies, Langton et al. (1977) successfully demonstrated the
growth of the red seaweed, Hypnea musciformis, cultured in tanks with shellfish
culture effluent. Alternatively, crops that would usually be classed as glycophytes,
such as the common tomato (Lycopersicon esculentum), the cherry tomato
(Lycopersicon esculentum var. Cerasiforme) and basil (Ocimum basilicum), can
achieve remarkably successful production levels at up to 4 g/L (4000 ppm) salinity
and are often referred to as having low-moderate levels of salt tolerance (not to be
confused with true halophytes, which are resistant to high salinities). Other crops that
are tolerant of low-moderate salinities include turnip, radish, lettuce, sweet potato,
broad bean, corn, cabbage, spinach, asparagus, beets, squash, broccoli and cucumber
(Kotzen and Appelbaum 2010; Appelbaum and Kotzen 2016). For example, Dufault
312 B. Kotzen et al.
et al. (2001) and Dufault and Korkmaz (2000) experimented with shrimp waste
(shrimp faecal matter and decomposed feed) as a fertilizer for broccoli (Brassica
oleracea italica) and bell pepper (Capsicum annuum) production, respectively.
Although their studies did not use maraponic techniques, they involved plants that
are commonly grown using aquaponic (freshwater) techniques. Therefore, due to
their salinity tolerance levels, these crops have enormous potential as candidate
species for production in haloponic systems using low to medium salinities.
Recently, a number of studies have shown that halophytes can be successfully
irrigated with aquacultural wastewater from marine systems using hydroponic tech-
niques or as part of a recirculating aquaculture system (RAS). Waller et al. (2015)
demonstrated the feasibility of nutrient recycling from a saltwater (16 psu salinity
[16,000 ppm]) RAS for European sea bass (D. labrax) through the hydroponic
production of three halophytic plants: Tripolium pannonicum (sea aster), Plantago
coronopus (buck’s horn plantain) and Salicornia dolichostachya (long spiked
glasswort).
The majority of the maraponic work conducted so far involves the integration of
two trophic levels – plants/algae and fish. However, an example of a system
incorporating more than two trophic levels can be seen in an experiment conducted
by Neori et al. (2000), who designed a small system for the intensive land-based
culture of Japanese abalone (Haliotis discus hannai), seaweeds (Ulva lactuca and
Gracilaria conferta) and pellet-fed gilthead bream (Sparus aurata). This system
consisted of unfiltered seawater (2400 L/day) pumped to two abalone tanks and
drained through a fish tank and finally through a seaweed filtration/production unit
before being discharged back to the sea. Filter feeding molluscs could also be used in
such a system. Kotzen and Appelbaum (2010) and Appelbaum and Kotzen (2016)
compared the growth of common vegetables using potable water and moderately
saline water (4187–6813 ppm) and found that basil (Ocimum basilicum), celery
(Apium graveolens), leeks (Allium ampeloprasum porrum), lettuce (Lactuca sativa –
various types), Swiss chard (Beta vulgaris. ‘cicla’), spring onions (Allium cepa) and
watercress (Nasturtium officinale) performed extremely well.
Maraponics (SAs) and haloponics offer a number of advantages over traditional
crop and fish production methods. Because they use saline water (marine to brack-
ish), there is a reduced dependence on freshwater, which in some parts of the world
has become a very limited resource. It is typically practiced in a controlled environ-
ment (e.g. a greenhouse; controlled flow-rate tanks) giving better opportunities for
intensive production. Many maraponic and haloponic systems are closed RAS with
organic and/or mechanical biofilters and subsequently, water reuse is high, waste-
water pollution is vastly reduced or eliminated, and contaminants are removed or
treated. Even systems that are not RAS can significantly reduce the excess nutrients
in the wastewater prior to discharge. Additionally, the occurrence of contaminants in
non-RAS maraponic and haloponic systems can be reduced or eliminated through
the use of water containing low levels of naturally occurring contaminants and the
use of alternatives aquafeeds that do not contain dioxins or PCDs (e.g. novel feeds
made from macroalgae). This improvement in water quality reduces the potential for
12 Aquaponics: Alternative Types and Approaches 313
disease occurrence and the need for antibiotic use is therefore vastly reduced. Due to
their versatile configuration and low water requirements, maraponics and haloponics
can be successfully implemented in a wide variety of settings, from fertile coastal
areas to arid deserts (Kotzen and Appelbaum 2010), as well as in urban or peri-urban
settlements. Another potential benefit is that many of the species that are suitable for
these systems have a high commercial value. For example, the euryhaline European
sea bass (Dicentrarchus labrax) and gilthead sea bream (Sparus aurata) can fetch a
market price of €9/kg and €6/kg, respectively. Additionally, edible halophytes tend
to have a high market price, with sea-agretti (Salsola soda), for example, having a
market price of €4–€4.5/kg and marsh samphire (Salicornia europaea) selling at
€18/kg in supermarkets.
The evidence is therefore compelling. Maraponics and haloponics provide a
dynamic and rapidly growing field that has the potential to provide a number of
services to communities, many of which are explored elsewhere in this publication.
12.5.1 Introduction
Whilst aquaponics can be seen as part of a global solution to increase food produc-
tion in more sustainable and productive ways and where growing more food in urban
areas is now recognized as part of the solution to food security and a global food
crisis (Konig et al. 2016), aquaponic systems can themselves become more produc-
tive and sustainable by adopting alternative growing technologies and learning from
emerging technologies such as vertical farming and living walls [LWs] (Khandaker
and Kotzen 2018). Additionally by being space-efficient, they can be better inte-
grated into urban areas.
In the developed world most aquaponic systems are placed in greenhouses in
order to control temperature; in northern Europe and North America for example,
winter temperatures are too cold in winter and in Mediterranean areas such as Spain,
Italy, Portugal, Greece and Israel, summer temperatures are too warm. There are of
course many additional advantages in growing food in controlled greenhouses, such
as the ability to regulate relative humidity and control air movement, to quarantine
fish as well as plants from diseases as well as pests and potentially being able to add
CO2, to aid plant growth. However, growing produce in a greenhouse can readily
raise costs through (a) the capital costs of the greenhouse (a broad estimate of US
$350/m2 Arnold 2017) and (b) allied infrastructure such as microclimate controls
which include heating and cooling systems and lighting. On top of the initial
infrastructure costs, there are also the specific greenhouse production costs which
include the energy/power supply for heating and cooling as well as lighting.
Most aquaponic systems such as the University of the Virgin Island (UVI) system
(Fig. 12.1), designed by Dr. James Rakocy and his colleagues, use horizontal grow
314 B. Kotzen et al.
Degassing Tank
Clarifying Filter for
Fish Tanks 1 and 4
1st Filter Tank
with Netting
Fish Tanks
Vegetable Raft Tanks 1, 2 and 3 1 and 4
5 1 2
Rao of Plants : Filter : Fish Tanks
Fig. 12.2 Schematic diagram of a typical UVI system illustrating the ratio of fish tanks/filters/plant
growing tanks which is 2:1:5. This shows that the greatest area is subsumed by the plants and it is in
this area that space savings may be considered. (Khandaker and Kotzen 2018)
1
Terapia Urbana S.L. produces a felt pocket type of living wall in Seville, Spain.
12 Aquaponics: Alternative Types and Approaches 315
Living Walls
Living walls have yet to be used in aquaponics except in a number of trial systems
such as at the University of Greenwich, London (Khandaker and Kotzen 2018).
Whereas most VFS use nutrient film technique (NFT) grow channels or encapsu-
lated mineral wool blocks, LWs sometimes also use soil type substrates in pots or
troughs, which provide the rooting medium. Whilst this is fine for growing
ornamental plants as well as vegetables and herbs, when coupled with fish tanks,
any addition of soil to the system may complicate the microbial character of the
system and be detrimental to the fish. This is however unknown and requires
research. Experiments undertaken at the University of Greenwich (Khandaker
and Kotzen 2018) indicate that from a number of single, inert substrates tested
(including hydroleica, perlite, straw, sphagnum moss, mineral wool and coconut
fibre), coconut fibre and then mineral wool were superior in terms of root pene-
tration and root growth in lettuce (Lactuca sativa).
Vertical v. Horizontal: Factors to Be Considered
There are four key aspects which need to be taken into account when comparing the
benefits (productivity and sustainability) of vertical growing, compared to horizontal
growing. These are (1) space, (2) lighting, (3) energy and (4) life cycle costs.
12 Aquaponics: Alternative Types and Approaches 317
1. Space
The benefits of being able to grow produce vertically, back to back, need to be
balanced with the amount of space that is required to provide an even spread of
lighting as well as the row space required for management and maintenance. The
width of a row in hydroponic systems varies. As noted the standard ZipGrowTM
system is approximately 0.5 metres, whereas the usual row width for growing
tomatoes and cucumbers hydroponically varies from 0.9 to 1.2 metres (Badgery-
Parker and James 2010). Growing smaller plants such as lettuce and herbs such as
basil, may allow for narrower rows, but of course row width must ensure that
produce is not compromised by moving items such as trolleys and scissor lifts. A
key issue with growing vertically is the conflict that occurs between having fixed
rows and fixed lighting, which needs to be located in the rows between the planting
facades. These lights will impede people movements and thus either the lights need
to be (i) part of the growing structure or (ii) retractable or movable, so that workers
can readily undertake tasks, or (iii) the planting structures are movable and the lights
remain static.
2. Lighting
Greenhouse production of vegetables and other plants rely on specific spatial
arrangements which allow for planting, management through growth and then
harvesting. The spatial arrangement will depend on the types of plants and the
types of mechanization that is installed. Additionally, growing efficiently relies on
the supplement of additional light of different types, which have their own pros and
cons. In general what these lights do is provide specific wavelengths for plant growth
and for fruit or flower production. Whereas it is relatively simple and more common
to evenly light plants grown horizontally, it is more of a challenge to evenly light a
vertical surface.
With regard to types of lighting, many producers have moved to or are tempted to
install LEDs (light-emitting diodes), due to their long lifespan, up to 50,000 hours or
more (Gupta 2017), their low power requirements and their recent reduction in cost.
Virsile et al. in Gupta (2017) note that most applications of LED lighting in
greenhouses choose the combinations of red and blue wavelengths with high photon
efficiency but that green and white light containing substantial amounts of green
wavelengths has a positive physiological impact on plants. However, the combina-
tion of blue and red lights creates a purplish-grey image, and this hampers the visual
evaluation of plant health. The type of wavelengths chosen is complex and can have
benefits at different stages in the plant’s life and even according to the cultivars of,
for example, lettuce. Red-leafed lettuces, for example, respond to blue LED lighting,
increasing their pigmentation (Virsile et al. in Gupta 2017). Additionally, blue LED
lighting can improve the nutritional quality of green vegetables, reducing nitrate
content, increasing antioxidants and phenolic and other beneficial compounds. The
light spectra also affect taste, shape and texture (Virsile et al. in Gupta 2017). The
costs of LEDs have dropped significantly and as the efficacy of LEDs has increased
so the break-even return time on investment has decreased (Bugbee in Gupta 2017).
318 B. Kotzen et al.
Other lighting of course exists and this includes fluorescent lighting, metal halide
(MH) lighting and high pressure sodium (HPS) lighting. The type of lighting that is
used in vertical farming and with living walls varies considerably depending on the
scale and location. Compact fluorescent lamps (CFLs) are relatively thin and can
easily fit into small spaces, but they require an inductive ballast to regulate current
through the tubes. CFLs use only 20–30% of an incandescent bulb and they last six to
eight times longer but they are almost 50% less efficient than LEDs. They are by far
the cheapest of the three major types of grow lights. HPS grow light technology is over
75 years old and is well established for growing under glass, but they produce a lot of
heat and are thus not suitable for vertical farming and living walls, where light needs to
be delivered quite close to the plants. The heat produced by LED grow lights, on the
other hand, is minimal. The cost however is higher than other two types, and eye
protection is needed for longer-term exposure to LEDs as the long-term exposure to
the light spectra can be damaging to the eyes. The arrangement of VFS units will
dictate the lighting arrangement but on the whole these are lit by LEDs. The method of
lighting living walls will depend on the height of the wall. The taller the wall the more
difficult it is to apply an even spread across the surface, although it should be noted
that the number of lights used should be no different to those used in horizontal grow
beds and if the wall is tall then the lights may need to be staggered. As most living
walls are located for aesthetic purposes, lighting needs to be kept as far as possible, out
of the way and the lighting has to not only provide adequate light for plant growth and
health, but also so that the plants look good (Fig. 12.4).
The advances in LED technology, where lighting frequencies and intensity can be
engineered to suit individual species and cultivars as well as their various life cycles
means that LEDs will become the technology of choice in the near future. This will
additionally be enhanced by reductions in costs.
3. Energy
More energy for lighting is likely to be required for VFS as well as LWs as even
natural lighting cannot be achieved over vertical surfaces. Additionally more
pumping power for irrigation will be required and this will be relative to the height
of the VFS or LWs.
4. Comparative Life Cycle Analysis (LCA)
Whilst there are numerous studies undertaken on life cycle analysis of aquaponics
and various aspects of aquaponic systems, there are no comparative studies that
compare vertical versus horizontal aquaponics. This has yet to be done. We are
getting to a point where vertical aquaponics is likely to warrant further testing and
research and in time vertical aquaponics, which couples vertical farming systems or
living wall systems with the fish tanks and filtration units, is likely to become more
mainstream, as long as these can be profitable and sustainable.
12.6.1 Introduction
Fig. 12.5 Biofloc technology (BFT) applied for marine shrimp culture in Brazil (a) and for tilapia
culture in Mexico (b) (Source: EMA-FURG, Brazil and Maurício G. C. Emerenciano)
The first commercial BFT operations and probably the most famous commenced
in the 1980s at the ‘Sopomer’ farm in Tahiti, French Polynesia, and in the early
2000s at the Belize Aquaculture farm or ‘BAL’, located in Belize, Central America.
The yields obtained using 1000 m2 concrete tanks and 1.6 ha lined grow-out ponds
were approximately 20–25 ton/ha/year with two crops at Sopomer and 11–26 ton/ha/
cycle at BAL, respectively. More recently, BFT has been successfully expanded in
large-scale shrimp farming in Asia, in South and Central America as well as in small-
scale greenhouses in the USA, Europe and other areas. At least in one phase
(e.g. nursery phase) BFT has been used with great success in México, Brazil,
Ecuador and Peru. For commercial-scale tilapia culture, farms in Mexico, Colombia
and Israel are using BFT with productions around 7 to 30 kg/m3 (Avnimelech 2015)
(Fig. 12.5b). Additionally, this technology has been used (e.g. in Brazil and Colom-
bia) to produce tilapia juveniles (~30 g) for further stock in cages or earthen ponds
(Durigon et al. 2017). BFT has mainly been applied to shrimp culture and to some
extent with tilapia. Other species have been tested and show promise, as noted for
silver catfish (Rhamdia quelen) (Poli et al., 2015), carp (Zhao et al., 2014),
piracanjuba (Brycon orbignyanus) (Sgnaulin et al., 2018), cachama (Colossoma
macropomum) (Poleo et al., 2011) and other crustacean species such as
Macrobrachium rosenbergii (Crab et al., 2010), Farfantepenaeus brasiliensis
(Emerenciano et al., 2012), F. paulensis (Ballester et al., 2010), Penaeus
semisulcatus (Megahed, 2010), L. stylirostris (Emerenciano et al., 2011) and
P. monodon (Arnold et al., 2006). The interest in BFT is evident by the increasing
number of universities and research centres carrying out research particularly in the
key fields of grow-out management, nutrition, reproduction, microbial ecology,
biotechnology and economics.
Microorganisms play a key role in BFT systems (Martinez-Cordoba et al. 2015). The
maintenance of water quality, mainly by the control of the bacterial community over
autotrophic microorganisms, is achieved using a high carbon to nitrogen ratio (C:N)
12 Aquaponics: Alternative Types and Approaches 321
Table 12.2 Recent studies around the world applying the BFT in aquaponic systems for different
aquatic and plant species
Aquatic
species Plant species Main results References
Tilapia Lettuce Biofloc technology did not improve lettuce pro- Rahman
duction as compared to conventional hydroponic (2010)
solution
Tilapia Lettuce Yield and visual quality of lettuce was improved Pinho
using BFT as compared to clear-water recirculation et al.
system (2017)
Tilapia Lettuce Plant performance (lettuce) using tilapia in a nurs- Pinho
(nursery) ery phase (1–30 g) was negatively influenced by (2018)
biofloc wastewater as compared to RAS wastewater
after two plant cycles (13 days each). Plant visual
aspects were better in RAS as compared to BFT
Tilapia Lettuce The presence of filtering elements (mechanical filter Barbosa
and biological filter) positively affected the lettuce (2017)
production in aquaponic systems as compared to
treatment without filters using BFT
Tilapia Lettuce Low salinity (3 ppt) can be performed in aquaponics Lenz et al.
using BFT. Visual and performance parameters (2017)
indicated that the purple variety had better perfor-
mance than the smooth and crisped varieties
Silver Lettuce The use of bioflocs in the aquaponic system may Rocha
catfish improve the productivity of lettuce in an integrated et al.
culture with silver catfish (2017)
Litopenaeus Sarcocornia The performance of marine shrimp L. vannamei was Pinheiro
vannamei ambigua not affected by the S. ambigua integrated et al.
aquaponics production and also improve the use of (2017)
nutrients (e.g. nitrogen) in the culture system
Fig. 12.6 Experimental aquaponics greenhouse comparing biofloc technology and RAS wastewa-
ter at Santa Catarina State University (UDESC), Brazil. (Source: Pinho et al. 2017)
higher microbial activity. However, this trend was not observed in the study by
Rahman (2010), who compared effluent from fish culture in a BFT system to a
conventional hydroponic solution in a lettuce production. In addition, Pinho
12 Aquaponics: Alternative Types and Approaches 323
Fig. 12.8 Aquaponics lettuce production integrated with tilapia using biofloc technology (left) and
accumulation of suspended solids in lettuce roots (right). Barbosa (2017)
12.7 Digeponics
It would be remiss in this chapter not to mention earthworms and their introduction
into aquaponics, and thus this chapter concludes with a brief résumé of these
detritivore invertebrates and their abilities to convert organic waste into fertilizer.
It is said that worms and the way that they digest matter were of interest to Aristotle
and Charles Darwin as well as the philosophers Pascal and Thoreau (Adhikary 2012)
and they were protected by law under Cleopatra. Earthworms are valued in agricul-
ture and horticulture as they are ‘vital to soil health because they transport nutrients
and minerals from below to the surface via their waste, and their tunnels aerate the
ground’ (National Geographic).
Modern vermiculture is attributed to Mary Appelhof, who in the early 1970s and
1980s produced a number of publications on composting with worms. Contempo-
rary vermicomposting occurs on large and small scales with the objective of getting
rid of organic waste and producing fertilizer in the forms of compost and ‘worm tea’.
Worm tea can be produced by soaking worm casts or by leaching the nutrients from
the compost through wetting or natural wetting leachate from precipitation.
Vermiponics uses the worm casts of mainly red wriggler worms also known as
tiger worms (Eisenia fetida) or (E. foetida) to provide nutrients in a hydroponic
system. When worms are introduced into an aquaponic system, we suggest that the
system is termed ‘vermi-aquaponics’ to differentiate the systems. It is thus the
introduction of worms into the growing beds of the plant parts of an aquaponic
system. It should be noted that vermi-aquaponics is in its infancy and mainly
practiced by hobbyists and in research laboratories. The worms are introduced
mainly into the plant growing media, usually gravel beds, where they can help to
break down any solid waste from the fish and any detritus from the plants and
additionally provide additional nutrients for the plants, and they can also be fed to
carnivore fish. In most instances the beds are of a flood and drain type, so that the
worms are not constantly under water.
Acknowledgements The authors thank National Council for Scientific and Technological
Development-CNPq (Project Number 455349/2012-6) and Scientific and Technological Research
Foundation of Santa Catarina State-FAPESC (Project Number 2013TR3406 and 2015TR453).
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Part III
Perspective for Sustainable Development
Chapter 13
Fish Diets in Aquaponics
Abstract Fish and feed waste provide most of the nutrients required by the plants in
aquaponics if the optimum ratio between daily fish feed inputs and the plant growing
area is sustained. Thus, the fish feed needs to fulfil both the fish’s and plant’s
nutritional requirements in an aquaponic system. A controlled fish waste production
strategy where the nitrogen, phosphorus and mineral contents of fish diets are
manipulated and used provides a way of influencing the rates of accumulation of
nutrients, thereby reducing the need for the additional supplementation of nutrients.
To optimize the performance and cost-effectiveness of aquaponic production, fish
diets and feeding schedules should be designed carefully to provide nutrients at the
right level and time to complement fish, bacteria and plants. To achieve this, a
species-specific tailor-made aquaponic feed may be optimized to suit the aquaponic
system as a whole. The optimal point would be determined based on overall system
performance parameters, including economic and environmental sustainability mea-
sures. This chapter thus focuses on fish diets and feed and reviews the state of the art
L. Robaina (*)
Aquaculture Research Group (GIA), Ecoaqua Institute, University of Las Palmas de Gran
Canaria, Telde, Gran Canaria, Spain
e-mail: lidia.robaina@ulpgc.es
J. Pirhonen
Department of Biological and Environmental Science, University of Jyväskylä, Jyväskylä,
Finland
e-mail: juhani.pirhonen@jyu.fi
E. Mente
Department of Ichthyology and Aquatic Environment, University of Thessaly, Volos, Greece
e-mail: emente@uth.gr
J. Sánchez
Department of Physiology, Faculty of Biology, Regional Campus of International Excellence
“Campus Mare Nostrum”, University of Murcia, Murcia, Spain
e-mail: javisan@um.es
N. Goosen
Department of Process Engineering, Stellenbosch University, Stellenbosch, South Africa
e-mail: njgoosen@sun.ac.za
13.1 Introduction
Aquatic food is recognized to be beneficial to human nutrition and health and will
play an essential role in future sustainable healthy diets (Beveridge et al. 2013). In
order to achieve this, the global aquaculture sector must contribute to increasing the
quantity and quality of fish supplies between now and 2030 (Thilsted et al. 2016).
This growth should be promoted not only by increasing the production and/or
number of species but also by systems diversification. However, fish from aquacul-
ture has only recently been included in the food security and nutrition (FSN) debate
and the future strategies and policies, demonstrating the important role of this
production to prevent malnutrition in the future (Bénét et al. 2015), as fish provide
a good source of protein and unsaturated fats, as well as minerals and vitamins. It is
important to note that many African nations are promoting aquaculture as the answer
to some of their current and future food production challenges. Even in Europe, fish
supply is currently not self-sufficient (with an unbalanced domestic supply/demand),
being increasingly dependent on imports. Therefore, ensuring the successful and
sustainable development of global aquaculture is an imperative agenda for the global
and European economy (Kobayashi et al. 2015). Sustainability is generally required
to show three key aspects: environmental acceptability, social equitability and
economic viability. Aquaponic systems provide an opportunity to be sustainable,
by combining both animal and plant production systems in a cost-efficient, environ-
mentally friendly and socially beneficial ways. For Staples and Funge-Smith (2009),
sustainable development is the balance between ecological well-being and human
well-being, and in the case of aquaculture, an ecosystem approach has been only
recently understood as a priority area for research.
Aquaculture has been the fastest growing food production sector during the last
40 years (Tveterås et al. 2012), being one of the most promising farming activities to
meet near-future world food needs (Kobayashi et al. 2015). Total production statis-
tics from aquaculture (FAO 2015) reveal an annual increment in global production
of 6%, which is expected to provide up to 63% of global fish consumption by 2030
(FAO 2014), for an estimated population of nine billion people in 2050. In the case
of Europe, the predicted increase is seen not only within the marine sector but also in
terrestrially produced products. Some of the expected challenges to the growth of
aquaculture during the coming years are the reduction in the use of antibiotics and
other pathological treatments, the development of efficient aquaculture systems and
equipment, together with species diversification and increased sustainability in the
13 Fish Diets in Aquaponics 335
area of feed production and feed use. The shift from fishmeal (FM) in feed to other
protein sources is also an important challenge, as well as the ‘fish-in-fish-out’ ratios.
There is a long history, reaching back to the 1960s, of promoting the growth of the
aquaculture sector towards proper sustainability including the encouragement to
adapt and create new and more sustainable feed formulas, reduce feed spilling and
reduce the food conversion ratio (FCR). Although aquaculture is recognized as the
most efficient animal production sector, when compared with terrestrial animal
production, there is still room for improvement in terms of resource efficiency,
diversification of species or methods of production, and moreover a clear need for
an ecosystem approach taking full advantage of the biological potential of the
organisms and providing adequate consideration of environmental and societal
factors (Kaushik 2017). This growth in aquaculture production will need to be
supported by an increase in the expected total feed production. Approximately
three million additional tons of feed will need to be produced each year to support
the expected aquaculture growth by 2030. Moreover, replacing fishmeal and fish oil
(FO) with plant and terrestrial substitutes is needed which requires essential research
into formula feed for animal farming.
The animal and aquafeed industries are part of a global production sector, which is
also the focus for future development strategies. Alltech’s yearly survey (Alltech
2017) reveals that total animal feed production broke through 1 billion metric tons,
with a 3.7% increase in production from 2015 despite a 7% decrease in the number of
feed mills. China and the USA dominated production in 2016, accounting for 35% of
the world’s total feed production. The survey indicates that the top 10 producing
countries have more than half of the world’s feed mills (56%) and account for 60% of
total feed production. This concentration in production means that many of the key
ingredients traditionally used in formulations for commercial aquaculture feeds are
internationally traded commodities, which subjects aquafeed production to any global
market volatility. Fishmeal for example is expected to double in price by 2030, whilst
fish oil is likely to increase by over 70% (Msangi et al. 2013). This illustrates the
importance of reducing the amount of these ingredients in fish feed whilst increasing
the interest and focus on new or alternative sources (García-Romero et al. 2014a, b;
Robaina et al. 1998, 1999; Terova et al. 2013; Torrecillas et al. 2017).
Whilst new offshore platforms have been developed for aquaculture production,
there is also a significant focus on marine and freshwater recirculating aquaculture
systems (RAS), as these systems use less water per kg fish feed used, which
increases fish production whilst reducing environmental impacts of aquaculture
including reductions in water usage (Ebeling and Timmons 2012; Kingler and
Naylor 2012). RAS can be integrated with plant production in aquaponic systems,
which readily fit into local and regional food system models (see Chap. 15) that can
be practised in or near large population centres (Love et al. 2015a). Water, energy
and fish feed are the three largest physical inputs for aquaponic systems (Love et al.
2014, 2015b). Approximately 5% of feed is not consumed by the farmed fish,
whilst the remaining 95% is ingested and digested (Khakyzadeh et al. 2015). Of
this share, 30–40% is retained and converted into new biomass, whilst the
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Aquaponic Technology
R+D+I Consortium Processing / Testing
Aquaponics
Technological Hydroponic
Innovation Agriculture
Validation/
Marketing
Upscaling
Economy Management
remaining 60–70% is released in the form of faeces, urine and ammonia (FAO
2014). On average, 1 kg of feed (30% crude protein) globally releases about 27.6 g
of N, and 1 kg of fish biomass releases about 577 g of BOD (biological oxygen
demand), 90.4 g of N and 10.5 g of P (Tyson et al. 2011).
Aquaponics is currently a small but rapidly growing sector which is clearly suited
to take advantage of the following political and socio-economic challenges, where 1)
aquatic produce meets the need for food security and nutrition, 2) fish self-sufficient
regions are established around the world, 3) aquaculture is a key sector but global
ingredients and global feed production comes under focus, 4) innovation in agricul-
ture promotes biodiversity in more sustainable ways and as part of the circular
economy and 5) there is a greater take up of locally produced foods. These aspects
tie in with the recommendations from the International Union for the Conservation
of Nature (Le Gouvello et al. 2017), regarded the sustainability of the aquaculture
and fish feed, which has recommended that efforts should be made to localize
aquaculture production and the circular approach, and for putting in place a quality
control programme for new products and by-products, as well as processing local
fish feed within regions. So far, aquaponics as ‘small-scale aquaculture farms’ could
provide examples for the implementation of the bioeconomy and local-scale
13 Fish Diets in Aquaponics 337
production, thus promoting ways of using products and by-products from organic
matter not suitable for use for other purposes, e.g. farmed insects and worms, macro-
and microalgae, fish and by-product hydrolysates, new agro-ecology-produced
plants and locally produced bioactives and micronutrients, whilst reducing the
environmental footprint with quality food (fish and plants) production and moving
towards zero waste generation. Moreover, aquaponics provides a good example for
promoting a multidisciplinary way of learning about sustainable production and
bioresource valorization, e.g. the ‘Islandap Project’ (INTERREG V-A MAC 2014-
2020) (Fig. 13.1).
The following sections of this chapter review the state of the art of fish diets,
ingredients and additives, as well as nutritional/sustainable challenges to consider
when producing specific aquaponic feeds.
Many studies have shown that FM can be successfully replaced by soybean meal in
aquafeeds, but soybean meal has anti-nutritional factors such as trypsin inhibitors,
soybean agglutinin and saponin, which limit its use and high replacement percentages
in farming carnivorous fish. High FM replacement by plant meals in fish diets can also
reduce nutrient bioavailability in fish, which results in nutrient alterations in the final
quality of the product (Gatlin et al. 2007). It can also cause undesirable disturbances to
the aquatic environment (Hardy 2010) and reduce fish growth due to the reduced
levels of essential amino acids (especially methionine and lysine), and reduced
palatability (Krogdahl et al. 2010). Gerile and Pirhonen (2017) noted that a 100%
FM replacement with corn gluten meal significantly reduced growth rate of rainbow
trout but FM replacement did not affect oxygen consumption or swimming capacity.
High levels of plant material can also affect the physical quality of the pellets, and
may complicate the manufacturing process during extrusion. Most of the alternative
plant-derived nutrient sources for fish feeds contain a wide variety of anti-nutritional
factors that interfere with fish protein metabolism by impairing digestion and
utilization, therefore leading to increased N release in the environment which can
affect fish health and welfare. In addition, diets including high levels of phytic acid
altered phosphorus and protein digestion that lead to high N and P release into the
surrounding environment. Feed intake and palatability, nutrient digestibility and
retention may vary according to fish species’ tolerance and levels and can change
the quantity and composition of the fish waste. Taking into consideration these
results, fish diet formulations in aquaponics should investigate ‘the tolerance’ dietary
levels of anti-nutritional factors (i.e. phytate) for different feed ingredients and for
each fish species used in aquaponics and also the effects of the addition of minerals
such as Zn and phosphate in the diets. It also should be noted that even if plant
material is regarded as an ecologically sound option to replace FM in aquafeeds,
plants need irrigation, and thus may induce ecological impacts in the form of their
water and ecological footprints (Pahlow et al. 2015) from nutrient run-off from the
fields.
Terrestrial animal by-products such as non-ruminant processed animal proteins
(PAPs) derived from monogastric farmed animals (e.g. poultry, pork) that are fit for
human consumption at the point of slaughter (Category 3 materials, EC regulation
142/2011; ΕC regulation 56/2013) could also replace FM and support the circular
economy. They have higher protein content, more favourable amino acid profiles and
fewer carbohydrates compared to plant feed ingredients whilst also lacking anti-
nutritional factors (Hertrampf and Piedad-Pascual 2000). It has been shown that
meat and bone meals may serve as a good phosphorus source when it is included
in the diet of Nile tilapia (Ashraf et al. 2013), although it has been strictly banned in the
feed of ruminant animals due to the danger of initiating bovine spongiform enceph-
alopathy (mad cow disease). Certain insect species, such as black soldier fly (Hermetia
illucens), could be used as an alternative protein source for sustainable fish feed diets.
The major environmental advantages of insect farming are that (a) less land and water
are required, (b) that greenhouse gas emissions are lower and that (c) insects have high
feed conversion efficiencies (Henry et al. 2015). However, there is a continuing need
13 Fish Diets in Aquaponics 339
for further research to provide evidence on quality and safety issues and screening for
risks to fish, plants, people and the environment.
It is important to note that fish cannot synthesize several essential nutrients
required for their metabolism and growth and depend on the feed for this supply.
However, there are certain animal groups that can use nutrient-deficient diets, as they
bear symbiotic microorganisms that can provide these compounds (Douglas 2010),
and thus, fish can obtain maximal benefit when the microbial supply of their essential
nutrients is scaled to demand. Undersupply limits fish growth, whilst oversupply can
be harmful due to the need for the fish to neutralize toxicity caused by non-essential
compounds. The extent to which the microbial function varies with the demands of
different fish species and what are the underlying mechanisms are largely unknown.
Importantly, an aquatic animal’s gut microbiota can in theory play a critical role in
providing the necessary nutrients and obtaining sustainability in fish farming
(Kormas et al. 2014; Mente et al. 2016). Further research in this field will help
facilitate the selection of ingredients to be used in fish feeds that promote gut
microbiota diversity to improve fish growth and health.
Research into the utilization of alternative plant and animal protein sources and
low trophic fish feed ingredients is ongoing. The substitution of marine sourced raw
ingredients in fish feed, which could be used directly for human food purposes
should decrease fishing pressure and contribute to preserving biodiversity. Low
trophic-level organisms, such as black soldier fly, which may serve as aquafeed
ingredients may be grown on by-products and waste of other agricultural industrial
practices given different nutritional quality meals, thereby adding additional envi-
ronmental benefits. However, efforts to succeed with the circular economy and the
recycling of organic and inorganic nutrients should be handled with care since
undesirable compounds in raw materials and seafood products could increase the
risk to animal health, welfare, growth performance and safety of the final product for
consumers. Research and continuous monitoring and reporting on contaminants of
farmed aquatic animals in relation to the maximum limits in feed ingredients and
diets are essential to inform revisions in and introductions of new regulations.
Since the end of the twentieth century, there have been significant changes in the
composition of aquafeeds but also advances in manufacturing. These transforma-
tions have originated from the need to improve the economic profitability of
aquaculture as well as to mitigate its environmental impacts. However, the driving
forces behind these changes is the need to decrease the amount of fishmeal (FM) and
fish oil (FO) in the feeds, which have traditionally constituted the largest proportion
of the feeds, especially for carnivorous fish and shrimp. Partly because of overfishing
but especially due to the continuous increase in global aquaculture volume, there is
340 L. Robaina et al.
4,0 0,40
3,0 0,30
Fish In - Fish Out
2,5 0,25
2,0 0,20
1,5 0,15
1,0 0,10
0,5 0,05
0,0 0,00
by-products from fish processing (offal and waste trimmings) are commonly used to
produce FM and FO. However, due to EU regulations (EC 2009), the use of FM of a
species is not allowed as feed for the same species, e.g. salmon cannot be fed FM
containing salmon trimmings.
FM and FO replacements with other ingredients can affect the quality of the
product that is sold to customers. Fish has the reputation of being a healthy food,
especially due to its high content of poly and highly unsaturated fatty acids. Most
importantly, seafood is the only source of EPA (eicosapentaenoic acid) and DHA
(docosahexaenoic acid), both of which are omega-3 fatty acids, and essential
nutrients for many functions in the human body. If FM and FO are replaced with
products from terrestrial origin, this will directly affect the quality of the fish flesh,
most of all its fatty acid composition, as the proportion of omega-3 fatty acids
(especially EPA and DHA) will decrease whilst the amount of omega-6 fatty acids
will increase along with the increase of plant material that is replacing FM and FO
(Lazzarotto et al. 2018). As such, the health benefits of fish consumption are partly
lost, and the product that ends up on the plate is not necessarily what consumers
expected to buy. However, in order to overcome the problem of decreased omega-3
fatty acids in the final product resulting from lower fish ingredients in aquafeeds, fish
farmers could employ so-called finishing diets with high FO content during the final
stages of cultivation (Suomela et al. 2017).
A new interesting option for replacing FO in fish feeds is the possibility of genetic
engineering, i.e. genetically modified plants which can produce EPA and DHA,
e.g. oil from genetically modified Camelina sativa (common name of camelina,
gold-of-pleasure or false flax which is known to have high levels of omega-3 fatty
acids) was successfully used to grow salmon, ending up with very high concentra-
tion on EPA and DHA in the fish (Betancor et al. 2017). The use of genetically
modified organisms in human food production, however, is subject to regulatory
approval and may not be an option in the short term.
Another new possibility to replace FM in aquafeeds is proteins made of
insects (Makkar et al. 2014). This new option has become possible within the EU
only recently when the EU changed legislation, allowing insect meals in aquafeeds
(EU 2017). The species permitted to be used are black soldier fly (Hermetia illucens),
common housefly (Musca domestica), yellow mealworm (Tenebrio molitor), lesser
mealworm (Alphitobius diaperinus), house cricket (Acheta domesticus), banded
cricket (Gryllodes sigillatus) and field cricket (Gryllus assimilis). Insects must be
reared on certain permitted substrates. Growth experiments done with different fish
species show that replacing FM with meal made of black soldier fly larvae does not
necessarily compromise growth and other production parameters (Van Huis and
Oonincx 2017). On the other hand, meals made of yellow mealworm could replace
FM only partially to avoid decrease in growth (Van Huis and Oonincx 2017).
However, FM replacement with insect meal can cause a drop in omega-3 fatty
acids, as they are void of EPA and DHA (Makkar and Ankers 2014).
In contrast to insects, microalgae typically have nutritionally favourable amino
acid and fatty acid (including EPA and DHA) profiles but there is also a wide
variation between species in this respect. Partial replacement of FM and FO in
342 L. Robaina et al.
2016; Delaide et al. 2017). A further challenge is the significant amounts of sodium
chloride in conventional fishmeal-based aquafeeds and the potential accumulation of
sodium in aquaponic systems (Treadwell et al. 2010). Different approaches can be
developed to address these challenges such as technological solutions,
e.g. decoupled aquaponic systems (Goddek et al. 2016) (also see Chap. 8), direct
nutrient supplementation in the plant production system via foliar spray or addition
to the recirculating water (Rakocy et al. 2006; Roosta and Hamidpour 2011) , or the
culture of better salt-tolerant plant (see Chap. 12). A new approach is the develop-
ment of tailored aquafeeds specifically for use in aquaponics.
In order to address plant nutrient shortages in aquaponics, tailored aquaponic
feeds need to increase the amount of plant-available nutrients, either by increasing
the concentrations of specific nutrients after excretion by the cultured animals, or by
rendering the nutrients more bio-available after excretion and biotransformation, for
rapid uptake by the plants. Achieving this increased nutrient excretion is, however,
not as simple as supplementing increased amounts of the desired nutrients to the
aquaculture diets, as there are many (often conflicting) factors that need to be
considered in an integrated aquaponic system. For example, although optimal
plant production will require increased concentrations of specific nutrients, certain
minerals, e.g. certain forms of iron and selenium, can be toxic to fish even at low
concentrations and would therefore have maximum allowable levels in the circulat-
ing water (Endut et al. 2011; Tacon 1987). Apart from total nutrient levels, the ratio
between nutrients (e.g. the P:N ratio) is also important for plant production (Buzby
and Lin 2014), and imbalances in the ratios between nutrients can lead to accumu-
lation of certain nutrients in aquaponic systems (Kloas et al. 2015). Furthermore,
even if an aquaponic feed increases plant nutrient levels, the overall system water
quality and pH still needs to be maintained within acceptable limits to ensure
acceptable animal production, efficient nutrient absorption by plant roots, optimal
operation of biofilters and anaerobic digesters (Goddek et al. 2015b; Rakocy et al.
2006) and to avoid precipitation of certain important nutrients like phosphates, as
this will render them unavailable to plants (Tyson et al. 2011). To achieve this
overall balance is no mean feat, as there are complex interactions between the
different forms of nitrogen in the system (NH3, NH4+, NO2 , NO3 ), the system
pH and the assortment of metals and other ions present in the system (Tyson et al.
2011; Goddek et al. 2015; Bittsanszky et al. 2016).
Common Nutrient Shortages in Aquaponic Systems
Plants require a range of macro- and micronutrients for growth and development.
Aquaponic systems are commonly deficient in the plant macronutrients potassium
(K), phosphorus (P), iron (Fe), manganese (Mn) and sulphur (S) (Graber and Junge
2009; Roosta and Hamidpour 2011). Nitrogen (N) is present in different forms in
aquaponic systems, and is excreted as part of the protein metabolism of the cultured
aquatic animals (Rakocy et al. 2006; Roosta and Hamidpour 2011; Tyson et al.
2011) after which it enters the nitrogen cycle in the integrated aquaponic environ-
ment. (Nitrogen is discussed in detail in Chap. 9 and is therefore excluded from the
present discussion.)
344 L. Robaina et al.
The use of selected specialist aquaculture feed additives can contribute to the
development of tailored aquafeeds specifically for aquaponics, by providing addi-
tional nutrients to the cultured aquatic animals and/or plants, or by adjusting the ratio
of nutrients. Aquaculture feed additives are diverse, with a wide range of functions
and mechanisms of working. Functions can be nutritive and non-nutritive, and the
additives can be targeted towards action in the feeds or towards the physiological
processes of the cultured aquatic animals (Encarnação 2016). For the purposes of
this chapter, emphasis is on three specific types of additives which could assist the
tailoring of aquaponic diets: (1) mineral supplements added directly to the feeds,
(2) minerals that are added co-incidentally as part of additives that serve a
non-mineral purpose and (3) additives which render minerals, which are already
present in the feeds, more available to the cultured aquatic animals and/or plants in
aquaponic systems.
1. Direct mineral supplementation in aquaponic feeds
Supplementing minerals directly in aquaculture diets used in aquaponic systems
is one potential method to either increase the amount of minerals excreted by the
cultured animals or to add specific minerals required by the plants in aquaponic
systems. Minerals are routinely added in the form of mineral premixes to aquaculture
diets, to supply the cultured aquatic animals with the essential elements required for
growth and development (Ng et al. 2001; NRC 2011). Any minerals not absorbed by
the fish during digestion are excreted, and if these are in the soluble (mostly ionic)
form in the aquaponic system, these are available for plant uptake (Tyson et al. 2011;
Goddek et al. 2015). It is unclear how feasible such an approach would be, as there is
scant information about the efficacy of adding mineral supplements to aquafeeds for
the purpose of enhancing aquaponic plant production. In general, mineral require-
ments and metabolism in aquaculture are poorly understood compared to terrestrial
animal production, and the feasibility of this approach is therefore not well
described. Potential advantages to this approach would be that it could prove to be
a fairly simple intervention to improve overall system performance, it could allow
supplementation of a wide range of nutrients, and it is likely to be relatively low cost.
However, substantial research is still required to avoid any major potential pitfalls
that may arise. One of these centres on the fact that the supplemented minerals
destined for the plants first need to pass through the digestive tract of the cultured
aquatic animals and these could either be absorbed fully or partially during this
passage. This could lead to unwanted accumulation of minerals in the aquatic
animals, or interference in normal intestinal nutrient and/or mineral absorption and
physiological processes (Oliva-Teles 2012). Significant interactions can occur
between dietary minerals in aquaculture diets (Davis and Gatlin 1996), and these
need to be determined before direct mineral supplementation in aquaponic diets can
be employed. Other potential effects may include altered physical structure and
chemosensory characteristics of the feeds, which in turn could affect feed palatabil-
ity. Clearly, there is still substantial research required before this method of tailoring
aquaponic feeds can be adopted.
13 Fish Diets in Aquaponics 345
The design of feeds for fish is crucial in aquaponics because fish feed is the single or
at least the main input of nutrients for both animals (macronutrients) and plants
(minerals) (Fig. 13.3).
Nitrogen is introduced to the aquaponic system through protein in fish feed which
is metabolized by fish and excreted in the form of ammonia. The integration of
recirculating aquaculture with hydroponics can reduce the discharge of unwanted
nutrients to the environment as well as generate profits. In an early economic study,
phosphorus removal in an integrated trout and lettuce/basil aquaponic system proved
to be cost-saving (Adler et al. 2000). Integrating fish feeding rates is also paramount
to fulfil the nutritional requirements of plants. Actually, farmers need to know the
amount of feed used in the aquaculture unit to calculate how much nutrient needs to
be supplemented to promote plant growth in the hydroponic unit. For instance, in a
13 Fish Diets in Aquaponics 347
optimize the performance and cost-effectiveness of aquaponic systems, fish diets and
feeding schedules should be designed carefully to provide nutrients at the right level
and the right time to complement both fish and plants.
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Chapter 14
Plant Pathogens and Control Strategies
in Aquaponics
14.1 Introduction
Nowadays, aquaponic systems are the core of numerous research efforts which aim
at better understanding these systems and at responding to new challenges of food
production sustainability (Goddek et al. 2015; Villarroel et al. 2016). The cumulated
number of publications mentioning “aquaponics” or derived terms in the title went
from 12 in early 2008 to 215 in 2018 (January 2018 Scopus database research
results). In spite of this increasing number of papers and the large area of study topics
they are covering, one critical point is still missing, namely plant pest management
(Stouvenakers et al. 2017). According to a survey on EU Aquaponic Hub members,
only 40% of practitioners have some notions about pests and plant pest control
(Villarroel et al. 2016).
In aquaponics, the diseases might be similar to those found in hydroponic systems
under greenhouse structures. Among the most problematic pathogens, in term of
spread, are hydrophilic fungi or fungus-like protists which are responsible for root or
collar diseases. To consider plant pathogen control in aquaponics, firstly, it is
important to differentiate between coupled and decoupled systems. Decoupled
systems allow disconnection between water from the fish and crop compartment
(see Chap. 8). This separation allows the optimisation and a better control of
different parameters (e.g. temperature, mineral or organic composition and pH) in
each compartment (Goddek et al. 2016; Monsees et al. 2017). Furthermore, if the
water from the crop unit does not come back to the fish part, the application of
phytosanitary treatments (e.g. pesticides, biopesticides and chemical disinfection
agents) could be allowed here. Coupled systems are built in one loop where water
recirculates in all parts of the system (see Chaps. 5 and 7). However, in coupled
systems, plant pest control is more difficult due to the both presence of fish and
beneficial microorganisms which transform fish sludge into plant nutrients. Their
existence limits or excludes the application of already available disinfecting agents
and chemical treatments. Furthermore no pesticides or biopesticides have been
specifically developed for aquaponics (Rakocy et al. 2006; Rakocy 2012; Somerville
et al. 2014; Bittsanszky et al. 2015; Nemethy et al. 2016; Sirakov et al. 2016).
Control measures are consequently mainly based on non-curative physical practices
(see Sect. 14.3.1) (Nemethy et al. 2016; Stouvenakers et al. 2017).
On the other hand, recent studies highlight that aquaponic plant production offers
similar yields when compared to hydroponics although concentrations of mineral
plant nutrients are lower in aquaponic water. Furthermore, when aquaponic water is
complemented with some minerals to reach hydroponic concentrations of mineral
nutritive elements, even better yields can be observed (Pantanella et al. 2010;
Pantanella et al. 2015; Delaide et al. 2016; Saha et al. 2016; Anderson et al. 2017;
14 Plant Pathogens and Control Strategies in Aquaponics 355
Wielgosz et al. 2017; Goddek and Vermeulen 2018). Moreover, some informal
observations from practitioners in aquaponics and two recent scientific studies
(Gravel et al. 2015; Sirakov et al. 2016) report the possible presence of beneficial
compounds and/or microorganisms in the water that could play a role in
biostimulation and/or have antagonistic (i.e. inhibitory) activity against plant path-
ogens. Biostimulation is defined as the enhancement of plant quality traits and plant
tolerance against abiotic stress using any microorganism or substance.
With regard to these aspects, this chapter has two main objectives. The first is to
give a review of microorganisms involved in aquaponic systems with a special focus
on plant pathogenic and plant beneficial microorganisms. Factors influencing these
microorganisms will be also considered (e.g. organic matter). The second is to
review available methods and future possibilities in plant diseases control.
Microorganisms are present in the entire aquaponics system and play a key role in
the system. They are consequently found in the fish, the filtration (mechanical and
biological) and the crop parts. Commonly, the characterisation of microbiota
(i.e. microorganisms of a particular environment) is carried out on circulating
water, periphyton, plants (rhizosphere, phyllosphere and fruit surface), biofilter,
fish feed, fish gut and fish faeces. Up until now, in aquaponics, most of microbial
research has focused on nitrifying bacteria (Schmautz et al. 2017). Thus, the trend at
present is to characterise microorganisms in all compartments of the system using
modern sequencing technologies. Schmautz et al. (2017) identified the microbial
composition in different parts of the system, whereas Munguia-Fragozo et al. (2015)
give perspectives on how to characterize aquaponics microbiota from a taxonomical
and functional point of view by using cutting-edge technologies. In the following
sub-sections, focus will be only brought on microorganisms interacting with plants
in aquaponic systems organised into plant beneficial and plant pathogenic
microorganisms.
the entire system extremely quickly. Once a plant is infected, the disease can rapidly
spread out the system, especially because of the water’s recirculation (Jarvis 1992;
Hong and Moorman 2005; Sutton et al. 2006; Postma et al. 2008; Vallance et al.
2010; Rakocy 2012; Rosberg 2014; Somerville et al. 2014). Though Oomycetes are
among the most prevalent pathogens detected during root diseases, they often form a
complex with other pathogens. Some Fusarium species (with existence of species
well adapted to aquatic environment) or species from the genera Colletotrichum,
Rhizoctonia and Thielaviopsis can be found as part of these complexes and can also
cause significant damage on their own (Paulitz and Bélanger 2001; Hong and
Moorman 2005; Postma et al. 2008; Vallance et al. 2010). Other fungal genera
like Verticillium and Didymella, but also bacteria, such as Ralstonia, Xanthomonas,
Clavibacter, Erwinia and Pseudomonas, as well as viruses (e.g. tomato mosaic,
cucumber mosaic, melon necrotic spot virus, lettuce infectious virus and tobacco
necrosis), can be detected in hydroponics or irrigation water and cause vessel, stem,
leaf or fruit damage (Jarvis 1992; Hong and Moorman 2005). However note that not
all microorganisms detected are damaging or lead to symptoms in the crop. Even
species of the same genus can be either harmful or beneficial (e.g. Fusarium, Phoma,
Pseudomonas). Disease agents discussed above are mainly pathogens linked to
water recirculation but can be identified in greenhouses also. Section 14.2.2 shows
the results of the first international survey on plant diseases occurring specifically in
aquaponics, while Jarvis (1992) and Albajes et al. (2002) give a broader view of
occurring pathogens in greenhouse structures.
In hydroponics or in aquaponic systems, plants generally grow under greenhouse
conditions optimized for plant production, especially for large-scale production
where all the environmental parameters are computer managed (Albajes et al.
2002; Vallance et al. 2010; Somerville et al. 2014; Parvatha Reddy 2016). However,
optimal conditions for plant production can also be exploited by plant pathogens. In
fact, these structures generate warm, humid, windless and rain-free conditions that
can encourage plant diseases if they are not correctly managed (ibid.). To counteract
this, compromises must be made between optimal plant conditions and disease
prevention (ibid.). In the microclimate of the greenhouse, an inappropriate manage-
ment of the vapour-pressure deficit can lead to the formation of a film or a drop of
water on the plants surface. This often promotes plant pathogen development.
Moreover, to maximise the yield in commercial hydroponics, some other parameters
(e.g. high plant density, high fertilisation, to extend the period production) can
enhance the susceptibility of plants to develop diseases (ibid.).
The question now is to know by which route the initial inoculum (i.e. the first step
in an epidemiological cycle) is brought into the system. The different steps in plant
disease epidemiological cycle (EpC) are represented in Fig. 14.1. In aquaponics, as
in greenhouse hydroponic culture, it can be considered that entry of pathogens could
be linked to water supply, introduction of infected plants or seeds, the growth
material (e.g. reuse of the media), air exchange (dust and particles carriage), insects
(vectors of diseases and particles carriage) and staff (tools and clothing) (Paulitz and
Bélanger 2001; Albajes et al. 2002; Hong and Moorman 2005; Sutton et al. 2006;
Parvatha Reddy 2016).
1
Inoculum
2 Plant Contact
3 6
Infection Release and Spread
Germ Tube Appressorium
Latency
4 Symptoms
5
Contagious Period
Infectious Tissues
Death
Fig. 14.1 Basic steps (1 to 6) in plant disease epidemiological cycle (EpC) according to Lepoivre
(2003). (1) Arrival of the pathogen inoculum, (2) contact with the host plant, (3) tissues penetration
and infection process by the pathogen, (4) symptoms development, (5) plant tissues that become
infectious, (6) release and spread of infectious form of dispersion
358 G. Stouvenakers et al.
Once the inoculum is in contact with the plant (step 2 in the EpC), several cases of
infection (step 3 in the EpC) are possible (Lepoivre 2003):
– The pathogen-plant relationship is incompatible (non-host relation) and disease
does not develop.
– There is a host relation but the plant does not show symptoms (the plant is tolerant).
– The pathogen and the plant are compatible but defence response is strong enough
to inhibit the progression of the disease (the plant is resistant: interaction between
host resistance gene and pathogen avirulence gene).
– The plant is sensitive (host relation without gene for gene recognition), and the
pathogen infects the plant, but symptoms are not highly severe (step 4 in the EpC).
– And lastly, the plant is sensitive and disease symptoms are visible and severe
(step 4 in the EpC).
Regardless of the degree of resistance, some environmental conditions or factors
can influence the susceptibility of a plant to be infected, either by a weakening of the
plant or by promoting the growth of the plant pathogen (Colhoun 1973; Jarvis 1992;
Cherif et al. 1997; Alhussaen 2006; Somerville et al. 2014). The main environmental
factors influencing plant pathogens and disease development are temperature, rela-
tive humidity (RH) and light (ibid.). In hydroponics, temperature and oxygen
concentrations within the nutrient solution can constitute additional factors (Cherif
et al. 1997; Alhussaen 2006; Somerville et al. 2014). Each pathogen has its own
preference of environmental conditions which can vary during its epidemiologic
cycle. But in a general way, high humidity and temperature are favourable to the
accomplishment of key steps in the pathogen’s epidemic cycle such as spore
production or spore germination (Fig. 14.1, step 5 in the EpC) (Colhoun 1973;
Jarvis 1992; Cherif et al. 1997; Alhussaen 2006; Somerville et al. 2014). Colhoun
(1973) sums up the effects of the various factors promoting plant diseases in soil,
whereas Table 14.1 shows the more specific or adding factors that may encourage
plant pathogen development linked to aquaponic greenhouse conditions.
In the epidemiological cycle, once the infective stage is reached (step 5 in the
EpC), the pathogens can spread in several ways (Fig. 14.1, step 6 in the EpC) and
infect other plants. As explained before, root pathogens belonging to Oomycetes
taxa can actively spread in the recirculating water by zoospores release (Alhussaen
2006; Sutton et al. 2006). For other fungi, bacteria and viruses responsible for root or
aerial diseases, the dispersion of the causal agent can occur by propagation of
infected material, mechanical wounds, infected tools, vectors (e.g. insects) and
particles (e.g. spores and propagules) ejection or carriage allowed by drought,
draughts or water splashes (Albajes et al. 2002; Lepoivre 2003).
During January 2018, the first international survey on plant diseases was made
among aquaponics practitioner members of the COST FA1305, the American
Aquaponics Association and the EU Aquaponics Hub. Twenty-eight answers were
14 Plant Pathogens and Control Strategies in Aquaponics 359
Table 14.1 Adding factors encouraging plant pathogen development under aquaponic greenhouse
structure compared to classical greenhouse culture
Promoting factor Profiting to Causes References
Nutrient film tech- Pythium spp., Easy spread by water Koohakan et al. (2004)
nique (NFT), Deep Fusarium spp. recirculation; possibility and Vallance et al.
flow technique of post contamination (2010)
(DFT) after a disinfection step;
poor content in oxygen in
the nutrient solution
Inorganic media Higher content in Unavailable organic Khalil and Alsanius
(e.g. rockwool) bacteria compounds in the media (2001), Koohakan
(no information et al. (2004), Vallance
about their possible et al. (2010)
pathogenicity)
Organic media Higher content in Available organic com- Koohakan et al.
(e.g. coconut fibre fungi; higher con- pounds in the media (2004), Khalil et al.
and peat) tent in Fusarium (2009), and Vallance
spp. for coconut et al. (2010)
fibre
Media with high Pythium spp. Zoospores mobility; plant Van Der Gaag and
water content and stress Wever (2005),
low content in Vallance et al. (2010),
oxygen and Khalil and
(e.g. rockwool) Alsanius (2011)
Media allowing lit- Pythium spp. Better condition for zoo- Sutton et al. (2006)
tle water move- spores dispersal and che-
ment motaxis movement; no
(e.g. rockwool) loss of zoospore flagella
High temperature Pythium spp. Plant stressed and optimal Cherif et al. (1997),
and low concentra- condition for Pythium Sutton et al. (2006),
tion of DO in the growth Vallance et al. (2010),
nutrient solution and Rosberg (2014)
High host plant Pathogens growth; Warm and humid Albajes et al. (2002)
density and diseases spread environment and Somerville et al.
resulting (2014)
microclimate
Deficiencies, Fungi, viruses and Plant physiological mod- Colhoun (1973),
excess or imbal- bacteria ifications (e.g. action on Snoeijers and
ance of macro/ defence response, tran- Alejandro (2000),
micronutrients spiration, integrity of cell Mitchell et al. (2003),
walls); plant morphologi- Dordas (2008),
cal modifications Veresoglou et al.
(e.g. higher susceptibility (2013), Somerville
to pathogens, attraction of et al. (2014), and
pests); nutrient resources Geary et al. (2015)
in host tissues for patho-
gens; direct action on the
pathogen development
cycle
360 G. Stouvenakers et al.
received describing 32 aquaponic systems from around the world (EU, 21; North
America, 5; South America, 1; Africa, 4; Asia, 1). The first finding was the small
response rate. Among the possible explanations for the reluctance to reply to the
questionnaire was that practitioners did not feel able to communicate about plant
pathogens because of a lack of knowledge on this topic. This had already been
observed in the surveys of Love et al. (2015) and Villarroel et al. (2016).
Key information obtained from the survey are:
– 84.4% of practitioners observe disease in their system.
– 78.1% cannot identify the causal agent of a disease.
– 34.4% do not apply disease control measures.
– 34.4% use physical or chemical water treatment.
– 6.2% use pesticides or biopesticides in coupled aquaponic system against plant
pathogens.
These results support the previous arguments saying that aquaponic plants do get
diseases. Yet, practitioners suffer from a lack of knowledge about plant pathogens
and disease control measures actually used are essentially based on non-curative
actions (90.5% of cases).
In the survey, a listing of plant pathogens occurring in their aquaponic system was
provided. Table 14.2 shows the results of this identification. To remedy the lack of
practitioner’s expertise about plant disease diagnostics, a second survey version was
Table 14.2 Results of the first identifications of plant pathogens in aquaponics from the 2018
international survey analysis and from existing literature
Plant host Plant pathogen References or survey results
Allium schoenoprasu Pythium sp.(b) Survey
Beta vulgaris (swiss chard) Erysiphe betae(a) Survey
Cucumis sativus Podosphaera xanthii(a) Survey
Fragaria spp. Botrytis cinerea(a) Survey
Lactuca sativa Botrytis cinerea(a) Survey
Bremia lactucae(a) Survey
Fusarium sp.(b) Survey
Pythium dissotocum(b) Rakocy (2012)
Pythium myriotylum(b) Rakocy (2012)
Sclerotinia sp.(a) Survey
Mentha spp. Pythium sp.(b) Survey
Nasturtium officinale Aspergillus sp.(a) Survey
Ocimum basilicum Alternaria sp.(a) Survey
Botrytis cinerea(a) Survey
Pythium sp.(b) Survey
Sclerotinia sp.(a) Survey
Pisum sativum Erysiphe pisi(a) Survey
Solanum lycopersicum Pseudomononas solanacearum(a) McMurty et al. (1990)
Phytophthora infestans(a) Survey
Plant pathogens identified by symptoms in the aerial plant part are annotated by (a) and in root part
by (b) in exponent
14 Plant Pathogens and Control Strategies in Aquaponics 361
sent with the aim to identify symptoms without disease name linkage (Table 14.3).
Table 14.2 mainly identifies diseases with specific symptoms, i.e. symptoms that can
be directly linked to a plant pathogen. It is the case of Botrytis cinerea and its typical
grey mould, powdery mildew (Erysiphe and Podosphaera genera in the table) and its
white powdery mycelium/conidia, and lastly Sclerotinia spp. and its sclerotia pro-
duction. The presence of 3 plant pathologists in the survey respondents expands the
list, with the identification of some root pathogens (e.g. Pythium spp.). General
symptoms that are not specific enough to be directly related to a pathogen without
further verification (see diagnosis in Sect. 14.3) are consequently found in
Table 14.3. But it is important to highlight that most of the symptoms observed in
this table could also be the consequence of abiotic stresses. Foliar chlorosis is one of
the most explicit examples because it can be related to a large number of pathogens
(e.g. for lettuces: Pythium spp., Bremia lactucae, Sclerotinia spp., beet western
yellows virus), to environmental conditions (e.g. temperature excess) and to mineral
deficiencies (nitrogen, magnesium, potassium, calcium, sulfur, iron, copper, boron,
zinc, molybdenum) (Lepoivre 2003; Resh 2013).
Table 14.3 Review of occurring symptoms in aquaponics from the 2018 international survey
analysis
Symptoms Plants species
Foliar chlorosis Allium schoenoprasum 1, Amaranthus viridis 1, Coriandrum sativum 1,
Cucumis sativus 1, Ocimum basilicum 6, Lactuca sativa 4, Mentha spp. 2,
Petroselinum crispum 1, Spinacia oleracea 2, Solanum lycopersicum 1,
Fragaria spp. 1
Foliar necrosis Mentha spp. 2, Ocimum basilicum 1,
Stem necrosis Solanum lycopersicum 1,
Collar necrosis Ocimum basilicum 1
Foliar Mosaic Cucumis sativus 1, Mentha spp. 1, Ocimum basilicum 1,
Foliar wilting Brassica oleracea Acephala group 1, Lactuca sativa 1, Mentha spp. 1,
Cucumis sativus 1, Ocimum basilicum 1, Solanum lycopersicum 1
Foliar, stem and collar Allium schoenoprasum 1, Capsicum annuum 1, Cucumis sativus 1,
mould Lactuca sativa 2, Mentha spp. 2, Ocimum basilicum 4, Solanum
lycopersicum 1
Foliar spots Capsicum annuum 1, Cucumis sativus 1, Lactuca sativa 2, Mentha spp. 1,
Ocimum basilicum 5
Damping off Spinacia oleracea 1, Ocimum basilicum 1, Solanum lycopersicum 1,
seedlings in general 5
Crinkle Beta vulgaris (swiss chard) 1, Capsicum annuum 1, Lactuca sativa 1,
Ocimum basilicum 1
Browning or Allium schoenoprasum 1, Amaranthus viridis 1, Beta vulgaris (swiss
decaying root chard) 1, Coriandrum sativum 1, Lactuca sativa 1, Mentha spp. 2,
Ocimum basilicum 2, Petroselinum crispum 2, Solanum lycopersicum 1,
Spinacia oleracea 1
Numbers in exponent represent the occurrence of the symptom for a specific plant on a total of
32 aquaponic systems reviewed
362 G. Stouvenakers et al.
Postma et al. (2008) and Vallance et al. (2010), microbial involvement in the
suppressive effect is generally verified via a destruction of the microbiota of the
soilless substrate by sterilisation first and eventually followed by a re-inoculation.
When compared with an open system without recirculation, suppressive activity in
soilless systems could be explained by the water recirculation (McPherson et al.
1995; Tu et al. 1999, cited by Postma et al. 2008) which could allow a better
development and spread of beneficial microorganisms (Vallance et al. 2010).
Since 2010, suppressiveness of hydroponic systems has been generally accepted
and research topics have been more driven on isolation and characterization of
antagonistic strains in soilless culture with Pseudomonas species as main organisms
studied. If it was demonstrated that soilless culture systems can offer suppressive
capacity, there is no similar demonstration of such activity in aquaponics systems.
However, there is no empiric indication that it should not be the case. This optimism
arises from the discoveries of Gravel et al. (2015) and Sirakov et al. (2016) described
in the second paragraph of this section. Moreover, it has been shown in hydroponics
(Haarhoff and Cleasby 1991 cited by Calvo-bado et al. 2003; Van Os et al. 1999) but
also in water treatment for human consumption (reviewed by Verma et al. 2017) that
slow filtration (described in Sect. 14.3.1) and more precisely slow sand filtration can
also act against plant pathogens by a microbial suppressive action in addition to
other physical factors. In hydroponics, slow filtration has been demonstrated to be
effective against the plant pathogens reviewed in Table 14.4. It is assumed that the
microbial suppressive activity in the filters is most probably due to species of
Bacillus and/or Pseudomonas (Brand 2001; Déniel et al. 2004; Renault et al.
2007; Renault et al. 2012). The results of Déniel et al. (2004) suggest that in
hydroponics, the mode of action of Pseudomonas and Bacillus relies on competition
for nutrients and antibiosis, respectively. However, additional modes of action could
be present for these two genera as already explained for Pseudomonas spp. Bacillus
species can, depending on the environment, act either indirectly by plant
biostimulation or elicitation of plant defences or directly by antagonism via produc-
tion of antifungal and/or antibacterial substances. Cell wall-degrading enzymes,
bacteriocins, and antibiotics, lipopeptides (i.e. biosurfactants), are identified as key
molecules for the latter action (Pérez-García et al. 2011; Beneduzi et al. 2012;
Table 14.4 Review of plant pathogens effectively removed by slow filtration in hydroponics
Plant pathogens References
Xanthomonas campestris Brand (2001)
pv. Pelargonii
Fusarium oxysporum Wohanka (1995), Ehret et al. (1999) cited by Ehret et al. (2001),
van Os et al. (2001), Déniel et al. (2004), and Furtner et al. (2007)
Pythium spp. Déniel et al. (2004)
Pythium aphanidermatum Ehret et al. (1999) cited by Ehret et al. (2001), and Furtner et al.
(2007)
Phytophthora cinnamomi Van Os et al. (1999), 4 references cited by Ehret et al. (2001)
Phytophthora cryptogea Calvo-bado et al. (2003)
Phytophthora cactorum Evenhuis et al. (2014)
364 G. Stouvenakers et al.
Narayanasamy 2013). All things considered, the functioning of a slow filter is not so
different from the functioning of some biofilters used in aquaponics. Furthermore,
some heterotrophic bacteria like Pseudomonas spp. were already identified in
aquaponics biofilters (Schmautz et al. 2017). This is in accordance with the results
of other researchers who frequently detected Bacillus and/or Pseudomonas in RAS
(recirculated aquaculture system) biofilters (Tal et al. 2003; Sugita et al. 2005;
Schreier et al. 2010; Munguia-Fragozo et al. 2015; Rurangwa and Verdegem
2015). Nevertheless, up until now, no study about the possible suppressiveness in
aquaponic biofilters has been carried out.
Good agricultural practices (GAP) for plant pathogens control are the various actions
aiming to limit crop diseases for both yield and quality of produce (FAO 2008). GAP
transposable to aquaponics are essentially non-curative physical or cultivation prac-
tices that can be divided in preventive measures and water treatment.
Preventive Measures
Preventive measures have two distinct purposes. The first is to avoid the entry of the
pathogen inoculum into the system and the second is to limit (i) plant infection,
14 Plant Pathogens and Control Strategies in Aquaponics 365
(ii) development and (iii) spread of the pathogen during the growing period. Pre-
ventive measures aiming to avoid the entry of the initial inoculum in the greenhouse
are, for example, a fallow period, a specific room for sanitation, room sanitation
(e.g. plant debris removal and surface disinfection), specific clothes, certified seeds,
a specific room for plant germination and physical barriers (against insect vectors)
(Stanghellini and Rasmussen 1994; Jarvis 1992; Albajes et al. 2002; Somerville et al.
2014; Parvatha Reddy 2016). Among the most important practices used for the
second type of preventive measures are, the use of resistant plant varieties, tools dis-
infection, avoidance of plant abiotic stresses, good plant spacing, avoidance of algae
development and environmental conditions management. The last measure,
i.e. environmental conditions management, means to control all greenhouse param-
eters in order to avoid or limit diseases by intervening in their biological cycle (ibid.).
Generally, in large-scale greenhouse structures, computer software and algorithms
are used to calculate the optimal parameters allowing both plant production and
disease control. The parameters measured, among others, are temperature (of the air
and the nutrient solution), humidity, vapour pressure deficit, wind speed, dew
probability, leaf wetness and ventilation (ibid.). The practitioner acts on these
parameters by manipulating the heating, the ventilation, the shading, the supplement
of lights, the cooling and the fogging (ibid.).
Water Treatment
Physical water treatments can be employed to control potential water pathogens.
Filtration (pore size less than 10 μm), heat and UV treatments are among the most
effective to eliminate pathogens without harmful effects on fish and plant health
(Ehret et al. 2001; Hong and Moorman 2005; Postma et al. 2008; Van Os 2009;
Timmons and Ebeling 2010). These techniques allow the control of disease out-
breaks by decreasing the inoculum, the quantity of pathogens and their proliferation
stages in the irrigation system (ibid.). Physical disinfection decreases water patho-
gens to a certain level depending on the aggressiveness of the treatment. Generally,
the target of heat and UV disinfection is the reduction of the initial microorganisms
population by 90–99.9% (ibid.). The filtration technique most used is slow filtration
because of its reliability and its low cost. The substrates of filtration generally used
are sand, rockwool or pozzolana (ibid.). Filtration efficiency is essentially dependent
on pore size and flow. To be effective as disinfection treatment, the filtration needs to
be achieved with a pore size less than 10 μm and a flow rate of 100 l/m2/h, even if
less binding parameters show satisfactory performances (ibid.). Slow filtration does
not eliminate all of the pathogens; more than 90% of the total aerobic bacteria remain
in the effluent (ibid.). Nevertheless, it allows a suppression of plant debris, algae,
small particles and some soil-borne diseases such as Pythium and Phytophthora (the
efficiency is genus dependent). Slow filters do not act only by physical action but
also show a microbial suppressive activity, thanks to antagonistic microorganisms,
as discussed in Sect. 14.2.3 (Hong and Moorman 2005; Postma et al. 2008; Van Os
2009; Vallance et al. 2010). Heat treatment is very effective against plant pathogens.
However it requires temperatures reaching 95 C during at least 10 seconds to
366 G. Stouvenakers et al.
suppress all kind of pathogens, viruses included. This practice consumes a lot of
energy and imposes water cooling (heat exchanger and transitional tank) before
reinjection of the treated water back into the irrigation loop. In addition, it has the
disadvantage of killing all microorganisms including the beneficial ones (Hong and
Moorman 2005; Postma et al. 2008; Van Os 2009). The last technique and probably
the most applied is UV disinfection. 20.8% of EU Aquaponics Hub practitioners use
it (Villarroel et al. 2016). UV radiation has a wavelength of 200 to 280 nm. It has a
detrimental effect on microorganisms by direct damage of the DNA. Depending on
the pathogen and the water turbulence, the energy dose varies between 100 and
250 mJ/cm2 to be effective (Postma et al. 2008; Van Os 2009).
Physical water treatments eliminate the most of the pathogens from the incoming
water but they cannot eradicate the disease when it is already present in the system.
Physical water treatment does not cover all the water (especially the standing water
zone near the roots), nor the infected plant tissue. For example, UV treatments often
fail to suppress Pythium root rot (Sutton et al. 2006). However, if physical water
treatment allows a reduction of plant pathogens, theoretically, they also have an
effect on nonpathogenic microorganisms potentially acting on disease suppression.
In reality, heat and UV treatments create a microbiological vacuum, whereas slow
filtration produces a shift in effluent microbiota composition resulting in a higher
disease suppression capacity (Postma et al. 2008; Vallance et al. 2010). Despite the
fact that UV and heat treatment in hydroponics eliminate more than 90% of
microorganisms in the recirculating water, no diminution of the disease suppressive-
ness was observed. This was probably due to a too low quantity of water treated and
a re-contamination of the water after contact with the irrigation system, roots and
plant media (ibid.).
Aquaponic water treatment by means of chemicals is limited in continuous
application. Ozonation is a technique used in recirculated aquaculture and in hydro-
ponics. Ozone treatment has the advantage to eliminate all pathogens including
viruses in certain conditions and to be rapidly decomposed to oxygen (Hong and
Moorman 2005; Van Os 2009; Timmons and Ebeling 2010; Gonçalves and Gagnon
2011). However it has several disadvantages. Introducing ozone in raw water can
produce by-products oxidants and significant amount of residual oxidants
(e.g. brominated compound and haloxy anions that are toxic for fish) that need to
be removed, by UV radiation, for example, prior to return to the fish part (reviewed
by Gonçalves and Gagnon 2011). Furthermore, ozone treatment is expensive, is
irritant for mucous membranes in case of human exposure, needs contact periods of
1 to 30 minutes at a concentration range of 0.1–2.0 mg/L, needs a temporal sump to
reduce completely from O3 to O2 and can oxidize elements present in the nutrient
solution, such as iron chelates, and thus makes them unavailable for plants (Hong
and Moorman 2005; Van Os 2009; Timmons and Ebeling 2010; Gonçalves and
Gagnon 2011).
14 Plant Pathogens and Control Strategies in Aquaponics 367
Pythium and Fusarium species and bacteria, where Pseudomonas, Bacillus and
Lysobacter are the genera most represented in the literature (Paulitz and Bélanger
2001; Khan et al. 2003; Chatterton et al. 2004; Folman et al. 2004; Sutton et al. 2006;
Liu et al. 2007; Postma et al. 2008; Postma et al. 2009; Vallance et al. 2010; Sopher
and Sutton 2011; Hultberg et al. 2011; Lee and Lee 2015; Martin and Loper 1999;
Moruzzi et al. 2017; Thongkamngam and Jaenaksorn 2017). The direct addition of
some microbial metabolites such as biosurfactants has also been studied
(Stanghellini and Miller 1997; Nielsen et al. 2006; Nielsen et al. 2006). Although
some microorganisms are efficient at controlling root pathogens, there are other
problems that need to be overcome in order to produce a biopesticide. The main
challenges are to determine the means of inoculation, the inoculum density, the
product formulation (Montagne et al. 2017), the method for the production of
sufficient quantity at low cost and the storage of the formulated product. Ecotoxi-
cological studies on fish and living beneficial microorganisms in the system are also
an important point. Another possibility that could be exploited is the use of a
complex of antagonistic agents, as observed in suppressive soil techniques (Spadaro
and Gullino 2005; Vallance et al. 2010). In fact, microorganisms can work in
synergy or with complementary modes of action (ibid.). The addition of amend-
ments could also enhance the BCA potential by acting as prebiotics (see Sect. 14.4).
humic acids are known to stimulate plant growth and sustain the plant under abiotic
stress conditions (Bohme 1999; du Jardin 2015). Proteins in the water can be used
by plants as an alternative nitrogen source thus enhancing their growth and
pathogen resistance (Adamczyk et al. 2010). In the recirculated water, the abun-
dance of free-living heterotrophic bacteria is correlated with the amount of bio-
logically available organic carbon and carbon-nitrogen ratio (C/N) (Leonard et al.
2000; Leonard et al. 2002; Michaud et al. 2006; Attramadal et al. 2012). In the
biofilter, an increase in the C/N ratio increases the abundance of heterotrophic
bacteria at the expense of the number of autotrophic bacteria responsible for the
nitrification process (Michaud et al. 2006; Michaud et al. 2014). As implied,
heterotrophic microorganisms can have a negative impact on the system because
they compete with autotrophic bacteria (e.g. nitrifying bacteria) for space and
oxygen. Some of them are plant or fish pathogens, or responsible for off-flavour
in fish (Chang-Ho 1970; Funck-Jensen and Hockenhull 1983; Jones et al. 1991;
Leonard et al. 2002; Nogueira et al. 2002; Michaud et al. 2006; Mukerji 2006;
Whipps 2001; Rurangwa and Verdegem 2015). However, heterotrophic microor-
ganisms involved in the system can also be positive (Whipps 2001; Mukerji 2006).
Several studies using organic fertilizers or organic soilless media, in hydroponics,
have shown interesting effects where the resident microbiota were able to control
plant diseases (Montagne et al. 2015). All organic substrates have their own
physico-chemical properties. Consequently, the characteristics of the media will
influence microbial richness and functions. The choice of a specific plant media
could therefore influence the microbial development so as to have a suppressive
effect on pathogens (Montagne et al. 2015; Grunert et al. 2016; Montagne et al.
2017). Another possibility of pathogen suppression related to organic carbon is the
use of organic amendments in hydroponics (Maher et al. 2008; Vallance et al.
2010). By adding composts in soilless media like it is common use in soil,
suppressive effects are expected (Maher et al. 2008). Enhancing or maintaining a
specific microorganism such as Pseudomonas population by adding some formu-
lated carbon sources (e.g. nitrapyrin-based product) as reported by Pagliaccia et al.
(2007) and Pagliaccia et al. (2008) is another possibility. The emergence of organic
soilless culture also highlights the involvement of beneficial microorganisms
against plant pathogens supported by the use of organic fertilizers. Fujiwara
et al. (2013), Chinta et al. (2014), and Chinta et al. (2015) reported that fertilization
with corn steep liquor helps to control Fusarium oxysporum f.sp. lactucae and
Botrytis cinerea on lettuces and Fusarium oxysporum f.sp. radicis-lycopersici on
tomato plants. And even if hardly advised for aquaponic use, 1 g/L of fish-based
soluble fertilizer (Shinohara et al. 2011) suppresses bacterial wilt on tomato caused
by Ralstonia solanacearum in hydroponics (Fujiwara et al. 2012).
Finally, though information about the impact of organic matter on plant protec-
tion in aquaponics is scarce, the various elements mentioned above show their
potential capacity to promote a system-specific and plant pathogen-suppressive
microbiota.
370 G. Stouvenakers et al.
This chapter aimed to give a first report of plant pathogens occurring in aquaponics,
reviewing actual methods and future possibilities to control them. Each strategy has
advantages and disadvantages and must be thoroughly designed to fit each case.
However, at this time, curative methods in coupled aquaponic systems are still
limited and new perspectives of control must be found. Fortunately, suppressiveness
in terms of aquaponic systems could be considered, as already observed in hydro-
ponics (e.g. in plant media, water, and slow filters). In addition, the presence of
organic matter in the system is an encouraging factor when compared to soilless
culture systems making use of organic fertilisers, organic plant media or organic
amendments.
For the future, it seems important to investigate this suppressive action followed
by identification and characterization of the responsible microbes or microbe
consortia. Based on the results, several strategies could be envisaged to enhance
the capacity of plants to resist pathogens. The first is biological control by
conservation, which means favouring beneficial microorganisms by manipulating
and managing water composition (e.g. C/N ratio, nutrients and gases) and param-
eters (e.g. pH and temperature). But identification of these influencing factors
needs to be realized first. This management of autotrophic and heterotrophic
bacteria is also of key importance to sustain good nitrification and keep healthy
fish. The second strategy is augmentative biological control by additional release
of beneficial microorganisms already present in the system in large numbers
(inundative method) or in small numbers but repeated in time (inoculation
method). But prior identification and multiplication of an aquaponic BCA should
be achieved. The third strategy is importation, i.e. introducing a new microorgan-
ism normally not present into the system. In this case, selection of a microorganism
adapted and safe for aquaponic environment is needed. For the two last strategies,
the site of inoculation in the system must be considered depending on the aim
desired. Sites where microbial activity could be enhanced are the recirculated
water, the rhizosphere (plant media included), the biofilter (such as in slow sand
filters where BCA addition is already tested) and the phyllosphere (i.e. aerial plant
part). Whatever the strategy, the ultimate goal should be to lead the microbial
communities to provide a stable, ecologically balanced microbial environment
allowing good production of both plant and fish.
To conclude, following the requirements of integrated plant pest management
(IPM) is a necessity to correctly manage the system and avoid development and
spread of plant diseases (Bittsanszky et al. 2015; Nemethy et al. 2016). The
principle of IPM is to apply chemical pesticides or other agents as a last resort
when economic injury level is reached. Consequently, control of pathogens will
need to be firstly based on physical and biological methods (described above), their
combination and an efficient detection and monitoring of the disease (European
Parliament 2009).
14 Plant Pathogens and Control Strategies in Aquaponics 371
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Chapter 15
Smarthoods: Aquaponics Integrated
Microgrids
Abstract With the pressure to transition towards a fully renewable energy system
increasing, a new type of power system architecture is emerging: the microgrid. A
microgrid integrates a multitude of decentralised renewable energy technologies
using smart energy management systems, in order to efficiently balance the local
production and consumption of renewable energy, resulting in a high degree of
flexibility and resilience. Generally, the performance of a microgrid increases with
the number of technologies present, although it remains difficult to create a fully
autonomous microgrid within economic reason (de Graaf F, New strategies for smart
integrated decentralised energy systems, 2018). In order to improve the self-
sufficiency and flexibility of these microgrids, this research proposes integrating a
neighbourhood microgrid with an urban agriculture facility that houses a decoupled
multi-loop aquaponics facility. This new concept is called Smarthood, where all
Food–Water–Energy flows are circularly connected. In doing so, the performance of
the microgrid greatly improves, due to the high flexibility present within the thermal
mass, pumps and lighting systems. As a result, it is possible to achieve 95.38%
power and 100% heat self-sufficiency. This result is promising, as it could pave the
way towards realising these fully circular, decentralised Food–Water–Energy
systems.
F. de Graaf (*)
Spectral, Amsterdam, The Netherlands
e-mail: florijn@spectral.energy
S. Goddek
Mathematical and Statistical Methods (Biometris), Wageningen University, Wageningen,
The Netherlands
e-mail: simon.goddek@wur.nl; simon@goddek.nl
15.1 Introduction
Switching towards a fully sustainable energy system will partly require switching
from a centralised generation and distribution system, towards a decentralised
system, due to the rise of decentralised energy generation technologies using wind
and rooftop solar radiation. In addition, integrating the heat and transport sectors into
the electricity system will lead to a very significant increase in peak demand. These
developments require massive and costly adaptations to the energy infrastructure,
while the utilisation of existing production assets is expected to drop from 55% to
35% by 2035 (Strbac et al. 2015). This poses a major challenge, but also an
opportunity: if the energy flows can be balanced locally in microgrids, the demand
for expensive infrastructure upgrade can be minimised, while providing extra sta-
bility to the main grid. For these reasons, ‘microgrids have been identified as a key
component of the Smart Grid for improving power reliability and quality, increasing
system energy efficiency’ (Strbac et al. 2015).
Microgrids can provide much-needed resilience and flexibility, and are therefore
likely to play an important role in the energy system of the future. It is estimated that
by 2050, over half of EU households will be generating their own electricity
(Pudjianto et al. 2007). Unlocking flexible resources within microgrids is therefore
needed in order to balance the intermittent renewable energy generation.
Urban agriculture systems, such as aquaponics (dos Santos 2016), can provide
this much-needed energy flexibility (Goddek and Körner 2019; Yogev et al. 2016).
Plants can grow within a wide range of external conditions, since they are used to
doing so in nature. The same applies to fish in an aquaculture system, which can
thrive in a broad temperature range. These flexible operating conditions allow for a
buffering effect on energy input requirements, which create a large degree of
flexibility within the system. The high thermal mass embodied by the aquaculture
system allows for vast amounts of heat to be stored within the system. The lights can
be turned on and off depending on the abundance of electricity, allowing for excess
electricity generation to essentially be curtailed by turning it into valuable biomass.
Pumps can be operated in synchronicity with peak power generation times
(e.g. noon) to limit net peak power (peak shaving). Optimal distillation units
(Chap. 8) also have a very flexible heat demand and can be turned off as soon as
there is an oversupply of heat or electricity (i.e. the heat pump would then convert
electric energy into thermal energy). All these aspects make aquaponic systems well-
suited to provide flexibility to a microgrid.
Next to providing flexibility in consumption, a multi-loop aquaponics system can
be further integrated to also provide flexibility in production. Biogas is produced as a
byproduct from the UASB in the aquaponic facility. This biogas can be combusted
in order to produce both heat and power, by incorporating a micro-CHP in the
microgrid. Integrating aquaponic systems within microgrids can therefore enhance
energy flexibility both on the demand and supply sides.
15 Smarthoods: Aquaponics Integrated Microgrids 381
.
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Fig. 15.1 The Food–Water–Energy nexus shows the interplay between energy, water and food
production (based on IRENA 2015)
382 F. de Graaf and S. Goddek
Heat
Pumps
Fuel Cells
Biomass
Distillation Grey&Black
Hydroponics UASBs
Desalination Water
Water
Outside
Aquaculture Rain Water Sanitation CW Tank
Crops
System
Nearby
Lake/Stream
Fig. 15.2 The integration of decoupled aquaponics systems (as described in Chap. 8) in a
decentralised local environment as designed for the Smarthoods concept. The green arrows show
to what extent an aquaponics system can interact with the overall system. The red arrows represent
heat flows, the blue arrows water flows and the yellow arrows power flows
crossovers between the energy and food systems. For instance, occurring biodegrad-
able waste streams can be treated in anaerobic reactors (e.g. UASBs) and generate
both biogas and bio-fertiliser (Goddek et al. 2018). Even the demineralized waste
sludge can be utilised as liquid manure on conventional cropland.
15 Smarthoods: Aquaponics Integrated Microgrids 383
Example 15.1
An early example of an urban integrated aquaponic microgrid development is
De Ceuvel, a previously abandoned shipyard in Amsterdam-North that has
been converted into a self-sufficient office space and recreational hub. De
Ceuvel serves as a testbed for new technologies and policies aimed at creating
a circular economy. It features an all-electric microgrid including solar PV,
heat pumps and peer-to-peer energy trading over the blockchain using their
own energy token: the Jouliette.1 A small aquaponic facility produces herbs
and vegetables for the on-site restaurant. The same restaurant utilises biogas
extracted from locally produced organic waste for their cooking activities as
well as space heating. In addition, there is a lab present that is used for testing
the water quality and extracting phosphates and nitrates.
Although De Ceuvel is currently not actively using the aquaponics facility
to increase the flexibility of its microgrid, sensors are being installed to
monitor the energy and nutrient flows in order to assess its performance.
This data will be used to aid in the development of newer and smarter urban
integrated aquaponics microgrids, such as the Smarthoods concept proposed in
this chapter. Early use cases found in urban living labs like De Ceuvel are
essential to the successful development of the Smarthoods concept (Fig. 15.3).
1
https://www.jouliette.net
384 F. de Graaf and S. Goddek
15.3 Goal
The goal of this research is to quantify the degree of self-sufficiency and flexibility
for a microgrid integrated with a decoupled multi-loop aquaponics system.
15.4 Method
An Energy System Model (ESM) was made that can simulate the energy flows of a
wide range of components, whose main specifications are shown in Table 15.2. The
ESM is capable of calculating energy flows for each component for each hour of the
year.
15 Smarthoods: Aquaponics Integrated Microgrids 385
Table 15.1 Food and energy requirements per persona/household in the Netherlands
Average (per
capita/year) Total (100 persons) Source
Food
Vegetable consump- 33 kga (whereas 7300 kg EFSA (2018)
tion (the Netherlands) 73 kg are
recommended)
Required greenhouse Approx. 4 m2 400 m2 Estimated based on min.
area consumption
recommendation
Fish consumption 20 kg 2000 kg FAO (2015)
Required aquaculture 0.2 m3 20 m3 Estimated
volumeb
Energy
Household electricity 3000 kWhe/house/ 150 MWhe/year CBS (2018)
consumption year
(Netherlands)
Household heat con- 6500 kWhth/house/ 325 MWhth/year CBS (2018)
sumption year
(Netherlands)
RAS electricity 0.05–0.15 kWe/m3 1–3 kWe (Espinal, pers.
consumption 8,76–28,26 MWhe/ communication)
year
a
The average Dutch person eats 50 kg of vegetables per year. However, only 33 kg of vegetables
that can be grown in hydroponics systems, which are fruiting vegetables 31.87 g/day, brassica
vegetables 22.11 g/day, leaf vegetables 12.57 g/day, legume vegetables 19.74 g/day, stem vegeta-
bles 4.29 g/day
b
Considering a max. fish density of 80 kg/m3
The energy system was modelled in MATLAB using energy profile data for
Amsterdam obtained through DesignBuilder. The numerical time-series model
incorporates a wide selection of energy technologies, listed in Table 15.2 with
their relevant specifications (Fig. 15.4).
The Energy System Model (ESM) uses simple conditional statements for the
decision-making process, i.e. it is a rule-based control system. In the current version
of this model, the control is centralised, with the objective of self-consumption
386 F. de Graaf and S. Goddek
Fig. 15.4 The aquaponics microgrid model (F. de Graaf 2018), showing the energy balances for
power (upper diagram) and heat (lower diagram) for the reference case (Amsterdam)
maximisation for the system as a whole (in a future version, the control architecture
will be decentralised, see Sect. 15.5). The conditional statements to achieve this can
be stated as follows:
1. Keep the heat storage to a minimum.
2. Forecast the predicted inflexible electricity production and consumption.
3. (a) If the battery will be full, turn on flexible consumption.
(b) If the battery will be empty, turn on flexible generation.
By keeping the heat storage to a minimum, the buffer for flexible energy
balancing is maximised. If there is an overproduction of inflexible electricity
(i.e. electricity production that cannot be flexibly scheduled or controlled, such as
solar or wind), the heat pump can be turned on to create a buffer provided by hot
water storage and the thermal mass of the aquaponic RAS system. Conversely, if
there is an underproduction of electricity, flexible generation such as the CHP and
the fuel cell can be turned on, thereby utilising the thermal storage capacity.
For both heat and power, the energy balance is equivalent to
Pgen, flex þ Pgen, inflex þ Pgrid ¼ Pcons, inflex þ Pcons, flex þ Pstorage ð15:1Þ
Flexible generations include the heat pump, Combined Heat and Power (CHP)
unit, fuel cell, battery and smart/flexible devices (e.g. aquaponic pumps). Wind, solar
photovoltaics (PV) and solar collectors are classified as inflexible generation.
Non-flexible devices make up the bulk of electricity consumption, especially in
winter (due to the need for instant lighting) (Fig. 15.5).
15 Smarthoods: Aquaponics Integrated Microgrids 387
Fig. 15.5 Example of the energy flows (Sankey diagram) of a possible integrated microgrid
configuration at De Ceuvel (de Graaf 2018), including a biodigester for the production of biogas.
This particular configuration does not include the Combined Heat and Power unit that is present
within the Smarthood concept, nor does it take into account a large aquaponics facility
15.5 Results
The total electrical and thermal consumption of both the houses and the aquaponic
greenhouse facility (modelled from the data in Tables 15.1 and 15.2) is shown in
Table 15.3. The aquaponic greenhouse facility is responsible for 38.3% of power
consumption and 51.4% of heat consumption. The power demand for an aquaponics
facility integrated in a residential microgrid is therefore slightly over one-third of the
total local energy demand, given that all of the residential energy and vegetable/fish
production is done locally. The heat demand comprises roughly 50% of the total heat
demand, which can be attributed for a large part to the distillation unit running on
high-temperature water.
As can be seen in Figs. 15.4 and 15.6, the Smarthoods energy system is capable of
balancing production and demand most of the time. The total share of imported
electricity from the grid is 4.62% for the reference case. At times, a slight imbalance
of power can be observed, which can be attributed to suboptimal control for the
current version of the model for the most part. The CHP, for instance, switches from
an on- to off-state multiple times over the course of several hours, resulting in an
overproduction of electricity. Such behaviour will not occur for a more optimised
control system, since the CHP can be ramped down in coordination with the heat
pump in order to deliver the precise amount of electricity and heat needed.
15.5.1 Flexibility
The system is highly flexible as a result of the CHP and the aquaponics facility with
its flexible lighting and pumps, and high thermal buffering capacity, as well as the
388 F. de Graaf and S. Goddek
Table 15.3 Electrical and thermal load for different aspects of the microgrid
Residential Aquaponic facility
Electrical average demand 17.2 kW 10.2 kW
Electrical peak demand 47.6 kWp 15.2 kWp
Electrical total demand 143.2 MWh/year 89.2 MWh/year
Thermal average demand 37.1 kW 39.3 kW
Thermal peak demand 148.4 kW 121.2 kW
Thermal total demand 325.0 MWhth/year 344.2 MWhth/year
Fig. 15.6 Time-series graphical diagrams for the power (top-left) and heat (bottom-left) energy
balances (in W) of the Smarthood system. Storage capacity (in kWh) is indicated on the right side
for power (top-right) and heat (bottom-right). The x-axis represents number of hours since the start
of the year. The black line represents the imbalance of energy
battery, and the hydrogen system. The aquaponic system, especially, greatly
increases the overall flexibility of the system, as it can function for a wide range of
energy input, as can be derived from Table 15.4. As a result of this flexibility, the
system manages to achieve near total (95.38%) power self-sufficiency and 100%
heat self-sufficiency.
15.6 Discussion
Self-Sufficiency The energy system proposed for the Smarthood concept is capable
of achieving near full grid-independence through the use of the flexibility provided
by the various system components. The aquaponic system, especially, has a positive
15 Smarthoods: Aquaponics Integrated Microgrids 389
effect on the overall flexibility of the system. With 95.38% power self-sufficiency,
this system performs better than any other economically feasible system assessed in
previous research (de Graaf 2018).
Control Architecture Facilitating a decentralised local energy economy, such as the
one proposed in the Smarthoods concept, requires a platform that keeps track of all
the peer-to-peer transactions occurring within the neighbourhood. The
corresponding peer-to-peer network can be classified as a multi-agent system
(MAS) approach, in which multiple nodes (e.g. households or utility buildings)
function as independent agents with their own objective (e.g. minimise cost or
maximise energy saving) and corresponding decision-making process. Such a
decentralised, multi-agent decision-making approach is necessary due to the com-
plexity of the system. There is simply too much information and too many variables
for the computation of a hierarchical, top-down and centralised control architecture.
Blockchain A blockchain-based multi-agent system control architecture could
potentially provide the necessary framework to accommodate a decentralised peer-
to-peer network. A vast number of distributed nodes ensure stability and security for
the network, and an alternative to mining can be used: minting. With minting,
tokens/coins are generated based on the data provided by a real-world device such
as a smart energy metre. Provided that these sources of information can be trusted,
i.e. that these devices can be tamper-proofed, a secure and independent ledger can be
created in which various stakeholders can exchange goods (e.g. electricity) and
390 F. de Graaf and S. Goddek
Example 15.2
A recent advancement within the regulatory framework in the Netherlands is
the introduction of the experimenteerregeling, an experimental law that allows
a small number of carefully selected projects (such as de Ceuvel, example Z.1)
to allow energy cooperatives to become their own distribution system opera-
tor, as if they were behind a single metre connection. This law is indicative of
the awareness amongst Dutch regulatory bodies of previously mentioned legal
barriers, and will therefore most likely lead to the current electricity law to be
revised in the near future in order to better accommodate microgrid
developments.
There are also some legal barriers in most EU countries with respect to reusing
treated black water for fish and plant production, as it has to be ensured that human
pathogens are fully eliminated. More information on the legal framework of
aquaponics can be found in Chap. 20.
15.7 Conclusions
The goal of this research was to quantify the degree of flexibility and self-sufficiency
that an aquaponics integrated microgrid can provide. In order to attain this answer, a
neighbourhood of 50 households was assumed a ‘Smarthood’, with a decoupled
multi-loop aquaponics facility present that is capable of providing fish and vegeta-
bles for all the 100 inhabitants of the Smarthood.
The results are promising: thanks to the high degree of flexibility inherent in the
aquaponic system as a result of high thermal mass, flexible pumps and adaptive
lighting, the overall degree of self-sufficiency is 95.38%, making it nearly
completely self-sufficient and grid independent. With the aquaponics system being
responsible for 38.3% of power consumption and 51.4% of heat consumption, the
impact of the aquaponics facility on the total system’s energy balance is very high.
Earlier research (de Graaf 2018) has indicated that it is very difficult to achieve
self-consumption levels over 60% without relying on an external biomass source to
drive a CHP. Even with this source included, the maximum techno-economically
feasible self-consumption did not exceed 89%. In the Smarthood, biomass inputs for
the CHP are partially derived from the aquaponic system itself, and the recycling of
grey and black water. A higher self-consumption combined with a lower dependence
on external biomass inputs, and a resulting self-consumption of 95%, makes the
proposed aquaponic-integrated microgrid perform better from a self-sufficiency
point of view than any other renewable microgrid known to the authors.
The authors of this chapter therefore strongly believe that with enough experi-
mentation, integrating aquaponic greenhouse systems within microgrids yields great
potential for creating highly self-sufficient Food–Water–Energy systems at a local
level.
392 F. de Graaf and S. Goddek
References
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Chapter 16
Aquaponics for the Anthropocene: Towards
a ‘Sustainability First’ Agenda
J. Gott (*)
Geography and Environment, University of Southampton, Southampton, UK
e-mail: j.gott@soton.ac.uk
R. Morgenstern
Department of Agriculture, University of Applied Sciences of South Westphalia, Soest,
Germany
e-mail: morgenstern.rolf@fh-swf.de
M. Turnšek
Faculty of Tourism, University of Maribor, Brežice, Slovenia
e-mail: maja.turnsek@um.si
16.1 Introduction
Key drivers stated for aquaponic research are the global environmental, social and
economic challenges identified by supranational authorities like the Food and
Agriculture Organization (FAO) of the United Nations (UN) (DESA 2015) whose
calls for sustainable and stable food production advance the ‘need for new and
improved solutions for food production and consumption’ (1) (Junge et al. 2017;
Konig et al. 2016). There is growing recognition that current agricultural modes of
production cause wasteful overconsumption of environmental resources, rely on
increasingly scarce and expensive fossil fuel, exacerbate environmental contamina-
tion and ultimately contribute to climate change (Pearson 2007). In our time of
‘peak-everything’ (Cohen 2012), ‘business as usual’ for our food system appears at
odds with a sustainable and just future of food provision (Fischer et al. 2007). A food
system revolution is urgently needed (Kiers et al. 2008; Foley et al. 2011), and as the
opening chapters (Chaps. 1 and 2) of this book attest, aquaponics technology shows
much promise. The enclosed systems of aquaponics offer an especially alluring
convergence of potential resolutions that could contribute towards a more sustain-
able future (Kőmíves and Ranka 2015). But, we ask, what kind of sustainable future
might aquaponics research and aquaponics technology contribute towards? In this
chapter, we take a step back to consider the ambitions of our research and the
functions of our technology.
In this chapter we situate current aquaponic research within the larger-scale shifts
of outlook occurring across the sciences and beyond due to the problematic that has
become known as ‘the Anthropocene’ (Crutzen and Stoermer 2000b). Expanding
well beyond the confines of its original geological formulation (Lorimer 2017), the
Anthropocene concept has become no less than ‘the master narrative of our times’
(Hamilton et al. 2015). It represents an urgent realisation that demands deep ques-
tions be asked about the way society organises and relates to the world, including the
modus operandi of our research (Castree 2015). However, until now, the concept has
been largely sidelined in aquaponic literature. This chapter introduces the
Anthropocene as an obligatory frame of reference that must be acknowledged for
any concerted effort towards future food security and sustainability.
We discuss how the Anthropocene unsettles some key tenets that have
underpinned the traditional agriscience of the Green Revolution (Stengers 2018)
and how this brings challenges and opportunities for aquaponic research.
Aquaponics is an innovation that promises to contribute much towards the impera-
tives of sustainability and food security. But this emergent field is in an early stage
that is characterised by limited resources, market uncertainty, institutional resistance
with high risks of failure and few success stories—an innovation environment where
hype prevails over demonstrated outcomes (König et al. 2018). We suggest this
situation is characterised by a misplaced techno-optimism that is unconducive to the
deeper shifts towards sustainability that are needed of our food system.
Given this, we feel the aquaponics research community has an important role to
play in the future development of this technology. We suggest a refocusing of
16 Aquaponics for the Anthropocene: Towards a ‘Sustainability First’ Agenda 395
aquaponics research around the key demands of our food system—sustainability and
food security. Such a task entails we more thoroughly consider the nature of
sustainability, and so we draw on the insights from the fields of sustainability science
and STS. Addressing sustainability in the Anthropocene obligates the need to attend
more holistically the interacting biophysical, social, economic, legal and ethical
dimensions that encroach on aquaponic systems (Geels 2011). This is no small
task that places great demands on the way we produce and use knowledge. For
this reason we discuss the need to develop what we call a ‘critical sustainability
knowledge’ for aquaponics, giving pointers for possible ways forward, which
include (1) expanding aquaponic research into an interdisciplinary research domain,
(2) opening research up to participatory approaches in real-world contexts and
(3) pursuing a solution-oriented approach for sustainability and food security
outcomes.
‘Today, humankind has begun to match and even exceed some of the great forces of
nature [...] [T]he Earth System is now in a no analogue situation, best referred to as a
new era in the geological history, the Anthropocene’ (Oldfield et al. 2004: 81).
The scientific proposal that the Earth has entered a new epoch—‘the
Anthropocene’—as a result of human activities was put forward at the turn of the
new millennium by the chemist and Nobel Laureate Paul Crutzen and biologist
Eugene Stoermer (Crutzen and Stoermer 2000a). Increasing quantitative evidence
suggests that anthropogenic material flows stemming from fossil fuel combustion,
agricultural production and mineral extraction now rival in scale those natural flows
supposedly occurring outside of human activity (Steffen et al. 2015a). This is a
moment marked by unprecedented and unpredictable climatic, environmental and
ecological events (Williams and Jackson 2007). The benign era of the Holocene has
passed, so the proposal claims; we have now entered a much more unpredictable and
dangerous time where humanity recognises its devastating capacity to destabilise
planetary processes upon which it depends (Rockström et al. 2009, Steffen et al.
2015b; See chapter 1). The Anthropocene is therefore a moment of realisation,
where the extent of human activities must be reconciled within the boundaries of
biophysical processes that define the safe operating space of a stable and resilient
Earth system (Steffen et al. 2015b).
A profound intertwining of the fates of nature and humankind has emerged
(Zalasiewicz et al. 2010). The growing awareness of environmental and human
calamity—and our belated, tangled role within it—puts to test our faith in the key
modernist assumption, namely, the dualisms separating humans from nature (Ham-
ilton et al. 2015). This is a shocking and unprecedented moment because modernist
epistemologies have proven exceedingly powerful, contributing significantly
towards the organisation of society to the present day (Latour 1993). Conceptions
of unique and stable human agency, the presumption of progressive norms such as
396 J. Gott et al.
liberty or universal dignity, and the existence of an objective world separate from
human doings are all put to test (Latour 2015; Hamilton et al. 2015).
This insight, without doubt, applies to the food system of which we all inherit.
The Green Revolution1 was underpinned with modern aspirations, being founded on
ideas such as linear notions of progress, the power of human reason and faith in the
inevitable technological resolution of human problems (Cota 2011). These concep-
tions, which have traditionally secured the role of science in society, begin to appear
increasingly unreliable with the advent of the Anthropocene (Savransky 2013;
Stengers 2015). The inconvenient truth is that the technoscientific interventions,
which have been implemented as modern agrarian solutions onto our world over the
last century, have carried with them serious and unexpected outcomes. What’s more,
these escalating biophysical disruptions (e.g. greenhouse gas emissions and nitrogen
and phosphorous cycle perturbations) that have only recently become perceived
must be added to a much broader series of environmental, biological and social
repercussions brought about by particular aspects of our modernised food system.
The Anthropocene problematic leaves little doubt that our contemporary food
system faces enormous challenges (Kiers et al. 2008; Baulcombe et al. 2009;
Pelletier and Tyedmers 2010). Prominent studies point to agriculture as the single
largest contributor to the rising environmental risks posed in the Anthropocene
(Struik and Kuyper 2014; Foley et al. 2011). Agriculture is the single largest user
of freshwater in the world (Postel 2003); the world’s largest contributor to altering
the global nitrogen and phosphorus cycles and a significant source (19–29%) of
greenhouse gas emissions (Vermeulen et al. 2012; Noordwijk 2014). Put simply,
‘agriculture is a primary driver of global change’ (Rockström et al. 2017:6). And yet,
it is from within the new epoch of the Anthropocene that the challenge of feeding
humanity must be resolved. The number of hungry people in the world persists at
approximately 900 million (FAO, Ifad and WFP. 2013). Even then, in order to feed
the world by 2050, best estimates suggest that production must roughly double to
keep pace with projected demands from population growth, dietary changes (partic-
ularly meat consumption) and increasing bioenergy use (Kiers et al. 2008;
Baulcombe et al. 2009; Pelletier and Tyedmers 2010; Kearney 2010). Complicating
matters even further is the need not simply to produce more, but also to manage the
entire food system more efficiently. In a world where 2 billion suffer from micro-
nutrient deficiencies, whilst 1.4 billion adults are over-nourished, the need for better
distribution, access and nutrition is glaring, as is the drastic need to reduce the
deplorable levels of waste (conservative estimates suggest 30%) in the farm-to-fork
supply chain (Parfitt et al. 2010; Lundqvist et al. 2008; Stuart 2009).
1
The Green Revolution refers to a set of research and technology transfer initiatives occurring from
the 1930s and the late 1960s that increased agricultural production worldwide, particularly in the
developing world. As Farmer (1986) describes, these initiatives resulted in the adoption of new
technologies, including: ‘New, high-yielding varieties of cereals... in association with chemical
fertilizers and agro-chemicals, and with controlled water-supply... and new methods of cultivation,
including mechanization. All of these together were seen as a “package of practices” to supersede
“traditional” technology and to be adopted as a whole’.
16 Aquaponics for the Anthropocene: Towards a ‘Sustainability First’ Agenda 397
The Anthropocene marks a step change in the relation between humans and our
planet. It demands a rethink of the current modes of production that currently propel
us on unsustainable trajectories. Until now, such reflexive commitments have not
been required of agriscience research and development. It is worth remembering that
the Green Revolution, in both its ambitions and methods, was for some time
uncontroversial; agriculture was to be intensified and productivity per unit of land
or labour increased (Struik 2006). Without doubt, this project, whose technological
innovations were vigorously promoted by governments, companies and foundations
around the world (Evenson and Gollin 2003), was phenomenally successful across
vast scales. More calories produced with less average labour time in the commodity
system was the equation that allowed the cheapest food in world history to be
produced (Moore 2015). In order to simplify, standardise and mechanise agriculture
towards increases in productivity per worker, plant and animal, a series of biophys-
ical barriers had to be overridden. The Green Revolution achieved this largely
through non-renewable inputs.
In the Anthropocene, this agricultural paradigm that marked the Green Revolu-
tion runs up against (geological) history. Growing awareness is that this
‘artificialised’ agricultural model, which substitutes each time more ecological
processes with finite chemical inputs, irrigation and fossil fuel (Caron et al. 2014),
literally undermines the foundations of future food provision. The biophysical
contradictions of late-capitalist industrial agriculture have become increasingly
conspicuous (Weis 2010). Moreover, the dramatic environmental, economic and
social consequences of contemporary models of high-intensity artificialised agricul-
ture have become an escalating concern for a globalised food system manifesting
accelerating contradictions (Kearney 2010; Parfitt et al. 2010).
During the post-war period (mid-40s–70s), secure economic growth was founded
on the accelerated extraction of fossil fuel, and as Cota (Cota 2011) notes,
agriscience development during this time progressed more in tune with the geo-
chemical sciences than the life sciences. Agricultural production designed around
398 J. Gott et al.
the cheapest maximum yields had been simplified and unified into monocrops, made
to depend on mechanisation and agrochemical products. Although highly effective
when first implemented, the efficiency of these commercial inputs has witnessed
diminishing returns (Moore 2015). Following the oil crises of the 70s, the
productivist ideals of the Green Revolution fell more upon the life sciences, partic-
ularly in the guise of agri-biotech, which has grown into a multibillion-dollar
industry.
Feeding the globe’s exploding population has been the key concern in a decade-
long productivist narrative that has served to secure the prominent position of
agricultural biotech in our current food system (Hunter et al. 2017). The great
shock is that this highly advanced sector has done little to improve intrinsic yields.
World agricultural productivity growth slowed from 3% a year in the 1960s to 1.1%
in the 1990s (Dobbs et al. 2011). Recently, the yields of key crops have in some
places approached plateaux in production (Grassini et al. 2013). Mainstream
agroscientists have voiced concern that the maximum yield potential of current
varieties is fast approaching (Gurian-Sherman 2009). On top of this, climate change
is estimated to have already reduced global yields of maize and wheat by 3.8% and
5.5%, respectively (Lobell et al. 2011), and some warn of sharp declines in crop
productivity when temperatures exceed critical physiological thresholds (Battisti and
Naylor 2009).
The waning efficiency gains of artificial inputs added to the biological limits of
traditional varieties is a situation that, for some, further underscores the need to
accelerate the development of genetically engineered varieties (Prado et al. 2014).
Even then, the greatest proponents of GM—the biotech firms themselves—are aware
that GM interventions rarely work to increase yield, but rather to maintain it through
pesticide and herbicide resistance (Gurian-Sherman 2009). As such, agricultural
production has become locked into a cycle that requires the constant replacement
of new crop varieties and product packages to overcome the growing negative
environmental and biological impingements upon yield [2]. Melinda Cooper’s
(2008: 19) influential analysis of agro-biotechnology has traced how neoliberal
modes of production become relocated ever more within the genetic, molecular
and cellular levels. As such, the commercialisation of agrarian systems increasingly
extends towards the capture of germplasm and DNA, towards ‘life itself’ (Rose
2009). Cooper’s (2008) diagnosis is that we are living in an era of capitalist delirium
characterised by its attempt to overcome biophysical limits of our earth through the
speculative biotechnological reinvention of the future. In this respect, some have
argued that rather than overcoming weaknesses of the conventional paradigm, the
narrow focus of GM interventions seems only to intensify its central characteristics
(Altieri 2007).
Amidst the deceleration of yield increases, the estimated targets of 60–100%
increases in production needed by 2050 (Tilman et al. 2011; Alexandratos and
Bruinsma 2012) appear increasingly daunting. As compelling and clear as these
targets may be, concerns have been raised that productivist narratives have eclipsed
other pressing concerns, namely, the environmental sustainability of production
(Hunter et al. 2017) and food security (Lawrence et al. 2013). The current
16 Aquaponics for the Anthropocene: Towards a ‘Sustainability First’ Agenda 399
agricultural paradigm has held production first and sustainability as a secondary task
of mitigation (Struik et al. 2014).
Thirty years of frustrated sustainability talk within the productivist paradigm are
testament to the severe difficulties for researchers and policymakers alike to bridge
the gap between sustainability theory and practice (Krueger and Gibbs 2007).
‘Sustainability’ as a concept had initially had revolutionary potential. Key texts
such as the Club of Rome’s The Limits of Growth (Meadows et al. 1972), for
instance, contained an imminent critique of global development narratives. But
researchers have pointed out the way that ‘sustainability’ throughout the 80s and
90s became assimilated into neoliberal growth discourse (Keil 2007). We now have
a situation where, on the one hand, global sustainability is almost unanimously
understood as a prerequisite to attain human development across all scales—from
local, to city, nation and the world (Folke et al. 2005)—whilst on the other, despite
substantial efforts in many levels of society towards the creation of a sustainable
future, key global-scale indicators show that humanity is actually moving away from
sustainability rather than towards it (Fischer et al. 2007). This is in spite of the
increasing regularity of high-profile reports that evermore underscore the grave risks
of existing trends to the long-term viability of ecological, social and economic
systems (Steffen et al. 2006; Stocker 2014; Assessment 2003; Stern 2008). This
situation—the widening gap between our current trajectory and all meaningful
sustainability targets—has been discussed as the so-called ‘paradox of sustainability’
(Krueger and Gibbs 2007). Prevailing discourse on food security and sustainability
continues to galvanise growth-oriented developmental imperatives (Hunter et al.
2017).
Agriscience research and development proliferated in accordance with the dom-
inant politico-economic structures that defined planetary development over the last
30 years (Marzec 2014). Although the negative effects of the so-called ‘Chicago
School’ of development have by now been well documented (Harvey 2007), bio-
technological innovation remains rooted within neoliberal discourse (Cooper 2008).
These narratives consistently present global markets, biotech innovation and multi-
national corporate initiatives as the structural preconditions for food security and
sustainability. The empirical credibility of such claims has long been challenged
(Sen 2001), but seem especially relevant amidst the accumulating history of chronic
distributional failures and food crises that mark our times. It is worth repeating
Nally’s (2011; 49) point: ‘The spectre of hunger in a world of plenty seems set to
continue into the 21st century. . . this is not the failure of the modern food regime, but
the logical expression of its central paradoxes’. The situation is one where malnu-
trition is seen no longer as a failure of an otherwise efficiently functioning system,
but rather as an endemic feature within the systemic production of scarcity (Nally
2011). In the face of such persisting inconsistencies, commentators note that neo-
liberal appeals to human prosperity, food security and green growth appear out of
touch and often ideologically driven (Krueger and Gibbs 2007).
The Anthropocene is a time where ecological, economic and social disaster walk
hand in hand as modern economies and institutions geared towards unlimited growth
crash against the finite biophysical systems of the earth (Altvater et al. 2016; Moore
400 J. Gott et al.
‘development’ like those put to work in the Green Revolution became seen—by
anthropologists, historians and indigenous communities alike—as a kind of modified
successor to pre-war colonial discourse (Scott 2008; Martinez-Torres and Rosset
2010). In anthropological terms, what these studies taught us was that although
modern agriculture was rooted in developmental narratives of universal prosperity,
in reality, ‘progress’ was achieved through the displacement or indeed destruction of
a great diversity of agricultural perspectives, practices, ecologies and landscapes. It
is for this reason Cota (2011: 6) reminds us of the importance of the critical work that
explicitly positioned the biopolitical paradigm of industrial agriculture ‘not first and
foremost as an economic kind of imperialism, but more profoundly as an epistemic
and culturally specific kind of imperialism’.
This is a key point. The Green Revolution was not merely a technical, nor
economic intervention, but involved the spread of a more profound reconfiguration
of the epistemological registers of food provision itself. It was a process that deeply
influenced the way agricultural knowledge was produced, propagated and
implemented. As Cota (2011: 6) explains: ‘the use of physicalist and probabilistic
discourse, a purely instrumental conception of nature and work, the implementation
of statistical calculations disconnected from local conditions, [as well as] the reliance
on models without recognizing historic specificities’ were all ways of enacting the
biopolitical agenda of the Green Revolution. This list of commitments describes the
fundamentals at the sharp end of the Green Revolution, but as we have seen, such
commitments alone have proven insufficient for the task of creating a just and
sustainable food system. It becomes apparent that any research agenda fit for the
Anthropocene must learn to move beyond the modern food paradigm by forging a
different research ethic with different commitments.
To claim that Agriculture is ‘at a crossroads’ (Kiers et al. 2008) does not quite do
justice to the magnitude of the situation. The gaping ‘sustainability gap’ (Fischer
et al. 2007) amidst unanimous calls for sustainability are increasingly being met with
common response amongst researchers: pleas for revolutionary measures and para-
digm shifts. Foley et al. (2011: 5) put it quite directly: ‘The challenges facing
agriculture today are unlike anything we have experienced before, and they require
revolutionary approaches to solving food production and sustainability problems. In
short, new agricultural systems must deliver more human value, to those who need it
most, with the least environmental harm’. Somehow, world agriculture’s current role
as the single largest driver of global environmental change must shift into a ‘critical
agent of a world transition’ towards global sustainability within the biophysical safe
operating space of the Earth (Rockström et al. 2017).
The Anthropocene lays steep demands: Agriculture must be intensified; it must
meet the needs of a growing population, but at the same time it is mandatory that the
pressures exerted by our food production systems stay within the carrying capacity
402 J. Gott et al.
of Planet Earth. It is increasingly understood that future food security depends on the
development of technologies that increase the efficiency of resource use whilst
simultaneously preventing the externalisation of costs (Garnett et al. 2013). The
search for alternatives to our current agricultural paradigm has brought to the fore
ideas such as agroecology (Reynolds et al. 2014) and ‘sustainable intensification’,
with the acknowledgement that real progress must be made towards ‘ecological
intensification’, that is, increasing agricultural output by capitalising on the ecolog-
ical processes in agroecosystems (Struik and Kuyper 2014).
There has been well-documented debate on what constitutes ‘sustainable inten-
sification’ (SI) of agriculture as well as the role it might play in addressing global
food security (Struik and Kuyper 2014; Kuyper and Struik 2014; Godfray and
Garnett 2014). Critics have cautioned against the top-down, global analyses that
are often framed in narrow, production-oriented perspectives, calling for a stronger
engagement with the wider literature on sustainability, food security and food
sovereignty (Loos et al. 2014). Such readings revisit the need for developing
regionally grounded, bottom-up approaches, with a growing consensus claiming
that an SI agenda fit for the Anthropocene does not entail ‘business-as-usual’ food
production with marginal improvements in sustainability but rather a radical rethink-
ing of food systems not only to reduce environmental impacts but also to enhance
animal welfare, human nutrition and support rural/urban economies with sustainable
development (Godfray and Garnett 2014).
While traditional ‘sustainable intensification’ (SI) has been criticised by some as
too narrowly focused on production, or even as a contradiction in terms altogether
(Petersen and Snapp 2015), others make it clear that the approach must be broadly
conceived, with the acknowledgement that there is no single universal pathway to
sustainable intensification (Garnett and Godfray 2012). Important here is the grow-
ing appreciation of ‘multifunctionality’ in agriculture (Potter 2004). If, during the
twentieth century, ‘Malthusian’ demographics discourse had secured the narrow
goal of agricultural development on increasing production, the growing rediscovery
of the multiple dimensions of farming currently taking place is altering the percep-
tion of the relationship between agriculture and society.
‘Multifunctionality’ as an idea was initially contested in the context of the
controversial GATT and WTO agricultural and trade policy negotiations (Caron
et al. 2008), but has since gained wide acceptance, leading to a more integrative view
of our food system (Potter 2004). In this view, progress in seeing agriculture as an
important type of ‘land use’ competing with other land functions (Bringezu et al.
2014) interrelates with a number of other perspectives. These have been
conceptualised through several important categories: (1) as a source of employment
and livelihood for a rural and future urban population (McMichael 1994); (2) as a
key part of cultural heritage and identity (van der Ploeg and Ventura 2014); (3) as the
basis of complex value chain interactions in ‘food systems’ (Perrot et al. 2011);
(4) as a sector in regional, national and global economies (Fuglie 2010); (5) as
modifier and storehouse of genetic resources (Jackson et al. 2010); (6) as a threat to
environmental integrity that exerts destructive pressures on biodiversity (Brussaard
et al. 2010; Smil 2011); and (7) as a source of greenhouse gas emissions (Noordwijk
16 Aquaponics for the Anthropocene: Towards a ‘Sustainability First’ Agenda 403
2014). This list is by no means comprehensive, but what is important is that each of
these interacting dimensions is understood to impact sustainability and food security
in one way or another and must be apprehended by serious attempts towards SI.
Sustainability outcomes are increasingly seen as a complex interplay between
local and global concerns (Reynolds et al. 2014). Biophysical, ecological and human
needs intermix within the complexities and idiosyncrasies of ‘place’ (Withers 2009).
The ‘one size fits all’ solutions, characteristics of the Green Revolution, fail to
acknowledge these unique sustainability potentials and demands. The result is that
changes in food production and consumption must be perceived through a multi-
plicity of scales and styles. To this end, Reynolds et al. (2014) suggest an approach
to sustainability that takes advantage of the insights of agroecological principles.
They forward a ‘custom-fit’ food production focus ‘explicitly tailored to the envi-
ronmental and cultural individuality of place and respectful of local resource and
waste assimilative limits, thus promoting biological and cultural diversity as well as
steady-state economics’.
If the issues at stake are inherently multidimensional, others have also underlined
that they are contested. Trade-offs between the plethora of biophysical and human
concerns are inevitable and often exceedingly complex. Sustainability thresholds are
diverse, often normative, and can seldom all be realised in full simultaneously
(Struik and Kuyper 2014). It has been emphasised that new directions towards
sustainability and food security require simultaneous change at the level of formal
and informal social rules and incentive systems (i.e. institutions) that orient human
interaction and behaviour, and hence that ‘institutional innovation’ is held to be a
key entry point in addressing challenges (Hall et al. 2001). Insomuch as the
complexity of sustainable intensification derives from human framings (which entail
and flow from contexts, identities, intentions, priorities and even contradictions),
they are, as Kuyper and Struik (2014: 72) put it, ‘beyond the command of science’.
Attempting to reconcile the many dimensions of food production towards sustain-
able ends and within the bounds of our finite planet involves a great deal of
uncertainty, irreducibility and contestation (Funtowicz and Ravetz 1995); it requires
an awareness and acknowledgement that such issues are shot through with political
implication.
Food systems and sustainability research have come a long way in expanding the
narrow focus of the Green Revolution, bringing greater clarity to the steep chal-
lenges we face in the pursuit of a more environmentally and socially sustainable food
system. Thanks to a broad range of work, it is now apparent that food production lies
at the heart of a nexus of interconnected and multi-scalar processes, on which
humanity relies upon to meet a host of multidimensional—often contradictory—
needs (physical, biological, economic, cultural). As Rockström et al. (2017: 7) have
stated: ‘World agriculture must now meet social needs and fulfil sustainability
criteria that enables food and all other agricultural ecosystem services (i.e., climate
stabilization, flood control, support of mental health, nutrition, etc.) to be generated
within a safe operating space of a stable and resilient Earth system’. It is precisely
within these recalibrated agricultural goals that aquaponics technology must be
developed.
404 J. Gott et al.
both sustainability values and love for tinkering with new technology; (e) interests of
urban developers to find economically viable solutions for vacant urban spaces and
greening of urban space; and (f) research communities focused on developing
technological solutions to impending sustainability and food security problems. To
a greater or lesser degree, the spectre of techno-optimistic hope permeates the
development of aquaponics.
Although the claims of techno-optimist positions are inspiring and able to
precipitate the investment of money, time and resources from diverse actors, the
potential for such standpoints to generate justice and sustainability has been
questioned on scales from local (Leonard 2013) and regional issues (Hultman
2013) to global imperatives (Hamilton 2013). And it is at this point, we might
consider the ambitions of our own field. A good starting point would be the
‘COST action FA1305’, which has been an important facilitator of Europe’s
aquaponic research output over recent years, with a number of publications acknowl-
edging the positive impact of the action in enabling research (Miličić et al. 2017;
Delaide et al. 2017; Villarroel et al. 2016). Like all COST actions, this EU-funded
transnational networking instrument has acted as a hub for aquaponic research in
Europe, galvanising and broadening the traditional networks amongst researchers by
bringing together experts from science, experimental facilities and entrepreneurs.
The original mission statement of COST action FA1305 reads as follows:
Aquaponics has a key role to play in food provision and tackling global challenges such as
water scarcity, food security, urbanization, and reductions in energy use and food miles.
The EU acknowledges these challenges through its Common Agriculture Policy and policies
on Water Protection, Climate Change, and Social Integration. A European approach is
required in the globally emerging aquaponics research field building on the foundations of
Europe’s status as a global centre of excellence and technological innovation in the domains
of aquaculture and hydroponic horticulture. The EU Aquaponics Hub aims to the develop-
ment of aquaponics in the EU, by leading the research agenda through the creation of a
networking hub of expert research and industry scientists, engineers, economists, aquacul-
turists and horticulturalists, and contributing to the training of young aquaponic scientists.
The EU Aquaponics Hub focuses on three primary systems in three settings; (1) “cities and
urban areas” – urban agriculture aquaponics, (2) “developing country systems” – devising
systems and technologies for food security for local people and (3) “industrial scale
aquaponics” – providing competitive systems delivering cost effective, healthy and sustain-
able local food in the EU. (http://www.cost.eu/COST_Actions/fa/FA1305, 12.10.2017,
emphasis added).
As the mission statement suggests, from the outset of COST action FA1305, high
levels of optimism were placed on the role of aquaponics in tackling sustainability
and food security challenges. The creation of the COST EU Aquaponics Hub was to
‘provide a necessary forum for ‘kick-starting’ aquaponics as a serious and poten-
tially viable industry for sustainable food production in the EU and the world’
(COST 2013). Indeed, from the authors’ own participation within COST FA1305,
our lasting experience was without doubt one of being part of a vibrant, enthused and
highly skilled research community that were more or less united in their ambition to
make aquaponics work towards a more sustainable future. Four years down the line
since the Aquaponic Hub’s mission statement was issued, however, the
16 Aquaponics for the Anthropocene: Towards a ‘Sustainability First’ Agenda 407
As we saw earlier, it has been stressed that the goal to move towards sustainable
intensification grows from the acknowledgment of the limits of the conventional
agricultural development paradigm and its systems of innovation. Acknowledging
the need for food system innovations that exceed the traditional paradigm and that
can account for the complexity arising from sustainability and food security issues,
Fischer et al. (2007) have called for no less than ‘a new model of sustainability’
altogether. Similarly, in their recent plea for global efforts towards sustainable
intensification, Rockström et al. (2017) have pointed out that a paradigm shift in
our food system entails challenging the dominant research and development patterns
that maintain the ‘productivity first’ focus whilst subordinating sustainability
agendas to a secondary, ‘mitigating’ role. Instead, they call for a reversal of this
paradigm so that ‘sustainable principles become the entry point for generating
productivity enhancements’. Following this, we suggest a sustainability first vision
for aquaponics as one possible orientation that can both offer coherence to the field
and guide its development towards the proclaimed goals of sustainability and food
security.
16 Aquaponics for the Anthropocene: Towards a ‘Sustainability First’ Agenda 409
As with most calls for sustainability, our sustainability first proposal might sound
rather obvious and unchallenging at first glance, if not completely redundant—
surely, we could say, aquaponics is all about sustainability. But history would
remind us that making sustainability claims is an agreeable task, whereas securing
sustainability outcomes is far less certain (Keil 2007). As we have argued, the
‘sustainability’ of aquaponics currently exists as potential. Just how this potential
translates into sustainability outcomes must be a concern for our research
community.
Our ‘sustainability first’ proposal is far from straightforward. First and foremost,
this proposal demands that, if our field is to justify itself on the grounds of
sustainability, we must get to grips with the nature of sustainability itself. In this
regard, we feel there is much to be learned from the growing arena of sustainability
science as well as Science and Technology Studies (STS). We will find that
maintaining a sustainability focus within aquaponic research represents a potentially
huge shift in the direction, composition and ambition of our research community.
Such a task is necessary if we are to direct the field towards coherent and realistic
goals that remain focussed on sustainability and food security outcomes that are
relevant for the Anthropocene.
Taking sustainability seriously is a massive challenge. This is because, at its core,
sustainability is fundamentally an ethical concept raising questions about the value
of nature, social justice, responsibilities to future generations, etc. and encompasses
the multidimensional character of human-environment problems (Norton 2005). As
we discussed earlier, the sustainability thresholds that might be drawn up concerning
agricultural practices are diverse and often cannot be reconciled in entirety, obligat-
ing the need for ‘trade-offs’ (Funtowicz and Ravetz 1995). Choices have to be made
in the face of these trade-offs and most often the criteria upon which such choices are
based depend not only upon scientific, technical or practical concerns but also on
norms and moral values. It goes without saying, there is little consensus on how to
make these choices nor is there greater consensus on the norms and moral values
themselves. Regardless of this fact, inquiries into values are largely absent from the
mainstream sustainability science agenda, yet as Miller et al. (2014) assert, ‘unless
the values [of sustainability] are understood and articulated, the unavoidable political
dimensions of sustainability will remain hidden behind scientific assertions’. Such
situations prevent the coming together of and democratic deliberation between
communities—a certain task for achieving more sustainable pathways.
Taking note of the prominent place of values in collective action towards
sustainability and food security, scholars from the field of science and technology
studies have highlighted that rather than be treated as an important externality to
research processes (often dealt with separately or after the fact), values must be
moved upstream in research agendas (Jasanoff 2007). When values become a central
part of sustainability research, along comes the acknowledgement that decisions can
no longer be based on technical criteria alone. This has potentially huge impacts on
the research process, because traditionally what might have been regarded as the sole
remit of ‘expert knowledge’ must now be opened up to other knowledge streams (for
instance, ‘lay’, indigenous and practitioner knowledge) with all the epistemological
410 J. Gott et al.
16.7.1 Partiality
model and experiment on these aspects of the food system. As Abson et al. (2017: 2)
point out: ‘Much scientific lead sustainability applications assume some of the most
challenging drivers of unsustainability can be viewed as “fixed system properties”
that can be addressed in isolation’. In pursuing the paths along which experimental
success is most often realised, ‘atomised’ disciplinary approaches neglect those areas
where other approaches might prove rewarding. Such epistemological ‘blind spots’
mean that sustainability interventions are often geared towards highly tangible
aspects that may be simple to envisage and implement, yet have weak potential for
‘leveraging’ sustainable transition or deeper system change (Abson et al. 2017).
Getting to grips with the limits and partialities of our disciplinary knowledge is one
aspect that we stress when we claim the need to develop a ‘critical sustainability
knowledge’ for aquaponics.
Viewed from disciplinary perspectives the sustainability credentials of aquaponic
systems can be more or less simple to define (for instance, water consumption,
efficiency of nutrient recycling, comparative yields, consumption of non-renewable
inputs, etc.). Indeed, the more narrowly we define the sustainability criteria, the more
straightforward it is to test such parameters, and the easier it is to stamp the claim of
sustainability on our systems. The problem is that we can engineer our way to a form
of sustainability that only few might regard as sustainable. To paraphrase Kläy et al.
(2015), when we transform our original concern of how to realise a sustainable food
system into a ‘matter of facts’ (Latour 2004) and limit our research effort to the
analysis of these facts, we subtly but profoundly change the problem and direction of
research. Such an issue was identified by Churchman (1979:4–5) who found that
because science addresses mainly the identification and the solution of problems,
and not the systemic and related ethical aspects, there is always the risk that the
solutions offered up may even increase the unsustainability of development—what
he called the ‘environmental fallacy’ (Churchman 1979).
We might raise related concerns for our own field. Early research in aquaponics
attempted to answer questions concerning the environmental potential of the technol-
ogy, for instance, regarding water discharge, resource inputs and nutrient recycling,
with research designed around small-scale aquaponic systems. Although admittedly
narrow in its focus, this research generally held sustainability concerns in focus.
Recently, however, we have detected a change in research focus. This is raised in
Chap. 1 of this book, whose authors share our own view, observing that research ‘in
recent years has increasingly shifted towards economic feasibility in order to make
aquaponics more productive for large-scale farming applications’. Discussions, we
have found, are increasingly concerned with avenues of efficiency and profitability
that often fix the potential of aquaponics against its perceived competition with other
large-scale production methods (hydroponics and RAS). The argument appears to be
that only when issues of system productivity are solved, through efficiency measures
and technical solutions such as optimising growth conditions of plants and fish,
aquaponics becomes economically competitive with other industrial food production
technologies and is legitimated as a food production method.
We would certainly agree that economic viability is an important constituent of
the long-term resilience and sustainability potential of aquaponics. However, we
16 Aquaponics for the Anthropocene: Towards a ‘Sustainability First’ Agenda 413
would caution against too narrowly defining our research ethic—and indeed, the
future vision of aquaponics—based on principles of production and profit alone. We
worry that when aquaponic research is limited to efficiency, productivity and market
competitiveness, the old logics of the Green Revolution are repeated and our claims
to food security and sustainability become shallow. As we saw earlier,
productionism has been understood as a process in which a logic of production
overdetermines other activities of value within agricultural systems (Lilley and
Papadopoulos 2014). Since sustainability inherently involves a complex diversity
of values, these narrow avenues of research, we fear, risk the articulation of
aquaponics within a curtailed vision of sustainability. Asking the question ‘under
what circumstances can aquaponics outcompete traditional large-scale food produc-
tion methods?’ is not the same as asking ‘to what extent can aquaponics meet the
sustainability and food security demands of the Anthropocene?’.
16.7.2 Context
The relevance of agroecological ideas need not be restricted to ‘the farm’; the nature
of closed-loop aquaponics systems demands a ‘balancing’ of co-dependent ecolog-
ical agents (fish, plants, microbiome) within the limits and affordances of each
particular system. Although the microbiome of aquaponics systems has only just
begun to be analysed (Schmautz et al. 2017), complexity and dynamism is expected
to exceed Recirculating Aquaculture Systems, whose microbiology is known to be
affected by feed type and feeding regime, management routines, fish-associated
microflora, make-up water parameters and selection pressure in the biofilters
(Blancheton et al. 2013). What might be regarded as ‘simple’ in comparison to
other farming methods, the ecosystem of aquaponics systems is nevertheless
dynamic and requires care. Developing an ‘ecology of place’, where context is
intentionality and carefully engaged with, can serve as a creative force in research,
including scientific understanding (Thrift 1999; Beatley and Manning 1997).
The biophysical and ecological dynamics of aquaponic systems are central to the
whole conception of aquaponics, but sustainability and food security potentials do
not derive solely from these parameters. As König et al. (2016) point out, for
aquaponic systems: ‘different settings potentially affects the delivery of all aspects
of sustainability: economic, environmental and social’ (König et al. 2016). The huge
configurational potential of aquaponics—from miniature to hectares, extensive to
intensive, basic to high-tech systems—is quite atypical across food production
technologies (Rakocy et al. 2006). The integrative character and physical plasticity
of aquaponic systems means that the technology can be deployed in a wide variety of
applications. This, we feel, is precisely the strength of aquaponic technology. Given
the diverse and heterogeneous nature of sustainability and food security concerns in
the Anthropocene, the great adaptability, or even ‘hackability’ (Delfanti 2013), of
aquaponics offers much potential for developing ‘custom-fit’ food production
(Reynolds et al. 2014) that is explicitly tailored to the environmental, cultural and
nutritional demands of place. Aquaponic systems promise avenues of food produc-
tion that might be targeted towards local resource and waste assimilative limits,
material and technological availability, market and labour demands. It is for this
reason that the pursuit of sustainability outcomes may well involve different tech-
nological developmental paths dependent upon locale (Coudel et al. 2013). This is a
point that is beginning to receive increasing acknowledgement, with some commen-
tators claiming that the urgency of global sustainability and food security issues in
the Anthropocene demand an open and multidimensional approach to technological
innovation. For instance, Foley et al. (2011:5) state: ‘The search for agricultural
solutions should remain technology neutral. There are multiple paths to improving
the production, food security and environmental performance of agriculture, and we
should not be locked into a single approach a priori, whether it be conventional
agriculture, genetic modification or organic farming’ (5) (Foley et al. 2011). We
would highlight this point for aquaponics, as König et al. (2018: 241) have already
done: ‘there are several sustainability problems which aquaponics could address, but
which may be impossible to deliver in one system setup. Therefore, future pathways
will always need to involve a diversity of approaches’.
16 Aquaponics for the Anthropocene: Towards a ‘Sustainability First’ Agenda 415
principle become more apparent and become viewed as barriers to productivity that
must be overcome. Framing the aquaponic problem like this results in solutions that
involve more technology: patented one-way valves, condensation traps, high-tech
oxygenators, LED lighting, additional nutrient dispensers, nutrient concentrators and
so on. These directions repeat the knowledge dynamic of modern industrial agricul-
ture that overly concentrated the expertise and power of food production systems
into the hands of applied scientists engaged in the development of inputs, equipment
and remote system management. We are unsure of how such technocratic measures
might fit within a research ethic that places sustainability first. This is not an
argument against high-tech, closed environment systems; we simply hope to empha-
sise that within a sustainability first paradigm, our food production technologies
must be justified on the grounds of generating context-specific sustainability and
food security outcomes.
Understanding that sustainability cannot be removed from the complexities of
context or the potentials of place is to acknowledge that ‘expert knowledge’ alone
cannot be held as guarantor of sustainable outcomes. This strikes a challenge to
modes of centralised knowledge production based on experiments under controlled
conditions and the way science might contribute to the innovation processes
(Bäckstrand 2003). Crucial here is the design of methodological systems that ensure
both the robustness and genericity of scientific knowledge is maintained along with
its relevance to local conditions. Moving to conceptions like this requires a huge
shift in our current knowledge production schemes and not only implies better
integration of agronomic with human and political sciences but suggests a path of
knowledge co-production that goes well beyond ‘interdisciplinarity’ (Lawrence
2015).
Here it is important to stress Bäckstrand’s (2003: 24) point that the incorporation
of lay and practical knowledge in scientific processes ‘does not rest on the assump-
tion that lay knowledge is necessarily “truer”, “better” or “greener”’. Rather, as
Leach et al. (2012: 4) point out, it stems from the idea that ‘nurturing more diverse
approaches and forms of innovation (social as well as technological) allows us to
respond to uncertainty and surprise arising from complex, interacting biophysical
and socioeconomic shocks and stresses’. Faced with the uncertainty of future
environmental outcomes in the Anthropocene, a multiplicity of perspectives can
prevent the narrowing of alternatives. In this regard, the potential wealth of exper-
imentation occurring in ‘backyard’ and community projects across Europe repre-
sents an untapped resource which has until now received little attention from
research circles. ‘The small-scale sector. . .’ Konig et al. (2018: 241) observe,
‘. . .shows optimism and a surprising degree of self-organization over the internet.
There might be room for creating additional social innovations’. Given the
multidimensional nature of issues in the Anthropocene, grassroots innovations,
like the backyard aquaponics sector, draw from local knowledge and experience
and work towards social and organisational forms of innovation that are, in the eyes
of Leach et al. (2012: 4), ‘at least as crucial as advanced science and technology’.
Linking with community aquaponics groups potentially offers access to vibrant local
food groups, local government and local consumers who are often enthusiastic about
16 Aquaponics for the Anthropocene: Towards a ‘Sustainability First’ Agenda 417
deviation from the traditional research routines of fact building and repeatability. A
third package encompasses research on political, administrative, technical and
financial obstacles. The intention here is to involve a wider collection of stake-
holders, from politicians and decision-makers to planners, operators and neighbours,
with research structures developed to bring together each of these specific perspec-
tives. Hopefully, this more holistic method opens a path to the ‘sustainability first’
approach proposed in this chapter.
16.7.3 Concern
market organisations as well as labour and land rights conditions (Röling 2009).
When the role of this wider framing is assumed only as an ‘enabling environment’,
often the result is that such considerations are left outside of the research effort. This
is a point which serves to easily justify the failure of technology-based, top-down
development drives (Caron 2000). In this regard, the techno-optimistic discourse of
contemporary aquaponics, in its failure to apprehend wider structural resistance to
the development of sustainable innovation, would serve as a case example.
As an important potential form of sustainable intensification, aquaponics needs to
be recognised as being embedded in and linked to different social, economic and
organisational forms at various scales potentially from household, value chain, food
system and beyond including also other political levels. Thankfully, moves towards
attending to the wider structural difficulties that aquaponic technology faces have
recently been made, with König et al. (2018) offering a view of aquaponics through
an ‘emerging technological innovation system’ lens. König et al. (2018) have shown
how the challenges to aquaponics development derive from: (1) system complexity,
(2) the institutional setting and (3) the sustainability paradigm it attempts to impact.
The aquaponic research field needs to respond to this diagnosis.
The slow uptake and high chance of failure that aquaponics technology currently
exhibits is an expression of the wider societal resistance that makes sustainable
innovation such a challenge, as well as our inability to effectively organise against
such forces. As König et al. (2018) note, the high-risk environment that currently
exists for aquaponic entrepreneurs and investors forces startup facilities across
Europe to focus on production, marketing and market formation, over the delivery
of sustainability credentials. Along these lines, Alkemade and Suurs (2012) remind
us, ‘market forces alone cannot be relied upon to realize desired sustainability
transitions’; rather, they point out, insight into the dynamics of innovation processes
is needed if technological change can be guided along more sustainable trajectories
(Alkemade and Suurs 2012).
The difficulties aquaponic businesses face in Europe suggest the field currently
lacks the necessary market conditions, with ‘consumer acceptance’—an important
factor enabling the success of novel food system technologies—acknowledged as
a possible problem area. From this diagnosis, there has been raised the problem of
‘consumer education’ (Miličić et al. 2017). Along with this, we would stress that
collective education is a key concern for questions of food system sustainability. But
accounts like these come with risks. It is easy to fall back on traditional modernist
conceptions regarding the role of science in society, assuming that ‘if only the public
understood the facts’ about our technology they would choose aquaponics over other
food production methods. Accounts like these assume too much, both about the
needs of ‘consumers’, as well as the value and universal applicability of expert
knowledge and technological innovation. There is a need to seek finer-grain and
more nuanced accounts of the struggle for sustainable futures that move beyond the
dynamic of consumption (Gunderson 2014) and have greater sensitivity to the
diverse barriers communities face in accessing food security and implementing
sustainable action (Carolan 2016; Wall 2007).
420 J. Gott et al.
Gaining insight into innovation processes puts great emphasis upon our
knowledge-generating institutions. As we have discussed above, sustainability
issues demand that science opens up to public and private participatory approaches
entailing knowledge co-production. But in terms of this point, it’s worth noting that
huge challenges lay in store. As Jasanoff (2007: 33) puts it: ‘Even when scientists
recognize the limits of their own inquiries, as they often do, the policy world,
implicitly encouraged by scientists, asks for more research’. The widely held
assumption that more objective knowledge is the key to bolstering action towards
sustainability runs contrary to the findings of sustainability science. Sustainability
outcomes are actually more closely tied deliberative knowledge processes: building
greater awareness of the ways in which experts and practitioners frame sustainability
issues; the values that are included as well as excluded; as well as effective ways
of facilitating communication of diverse knowledge and dealing with conflict if and
when it arises (Smith and Stirling 2007; Healey 2006; Miller and Neff 2013; Wiek
et al. 2012). As Miller et al. (2014) point out, the continuing dependence upon
objective knowledge to adjudicate sustainability issues represents the persistence of
the modernist belief in rationality and progress that underwrites almost all
knowledge-generating institutions (Horkheimer and Adorno 2002; Marcuse 2013).
It is here where developing a critical sustainability knowledge for aquaponics
shifts our attention to our own research environments. Our increasingly
‘neoliberalised’ research institutions exhibit a worrying trend: the rollback of public
funding for universities, the increasing pressure to get short-term results, the sepa-
ration of research and teaching missions, the dissolution of the scientific author, the
contraction of research agendas to focus on the needs of commercial actors, an
increasing reliance on market take-up to adjudicate intellectual disputes and the
intense fortification of intellectual property in the drive to commercialise knowledge,
all of which have been shown to impact on the production and dissemination of our
research, and indeed all are factors that impact the nature of our science (Lave et al.
2010). One question that must be confronted is whether our current research
environments are fit for the examination of complex sustainability and long-term
food security targets that must be part of aquaponic research. This is the key point we
would like to stress—if sustainability is an outcome of multidimensional collective
deliberation and action, our own research endeavours, thoroughly part of the pro-
cess, must be viewed as something that can be innovated towards sustainability
outcomes also. The above-mentioned Horizon 2020 project proGIreg may be an
example of some ambitious first steps towards crafting new research environments,
but we must work hard to keep the research process itself from slipping out of view.
Questions might be raised about how these potentially revolutionary measures of
‘living labs’ might be implemented from within traditional funding logics. For
instance, calls for participatory approaches foreground the conceptual importance
of open-ended outcomes, while at the same time requiring the intended spending of
such living labs to be predefined. Finding productive ways out of traditional insti-
tutional barriers is an ever-present concern.
Our modern research environments can no longer be regarded as having a
privileged isolation from the wider issues of society. More than ever our
16 Aquaponics for the Anthropocene: Towards a ‘Sustainability First’ Agenda 421
control over their food production and distribution (Laidlaw and Magee 2016). Food
sovereignty has become a huge topic that precisely seeks to intervene into food
systems that are overdetermined by disempowering capitalist relations. From food
sovereignty perspectives, the corporate control of the food system and the commod-
ification of food are seen as predominant threats to food security and the natural
environment (Nally 2011). We would follow Laidlaw and Magee’s (2016) view that
community-based aquaponics enterprises ‘represent a new model for how to blend
local agency with scientific innovation to deliver food sovereignty in cities’.
Developing a ‘critical sustainability knowledge’ for aquaponics means resisting
the view that society and its institutions are simply neutral domains that facilitate the
linear progression towards sustainable innovation. Many branches of the social
sciences have contributed towards an image of society that is infused with asym-
metric power relations, a site of contestation and struggle. One such struggle
concerns the very meaning and nature of sustainability. Critical viewpoints from
wider fields would underline that aquaponics is a technology ripe with both political
potential and limitation. If we are serious about the sustainability and food security
credentials of aquaponics, it becomes crucial that we examine more thoroughly how
our expectations of this technology relate to on-the-ground experience, and in turn,
find ways of integrating this back into research processes. We follow Leach et al.
(2012) here who insist on the need for finer-grained considerations regarding the
performance of sustainable innovations. Apart from the claims, just who or what
stands to benefit from such interventions must take up a central place in the
aquaponic innovation process. Lastly, as the authors of Chap. 1 have made clear,
the search for a lasting paradigm shift will require the ability to place our research
into policy circuits that make legislative environments more conducive to
aquaponics development and enable larger-scale change. Influencing policy requires
an understanding of the power dynamics and political systems that both enable and
undermine the shift to sustainable solutions.
our hopes are not to get lost in the hype bubble of hollow sustainability chatter that
marks our neoliberal times, we have to demonstrate that aquaponics offers some-
thing different. As a final remark, we revisit de la Bellacasa’s (2015) point that:
‘agricultural intensification is not only a quantitative orientation (yield increase), but
entails a “way of life”’. If this is the case, then the pursuit of sustainable intensifi-
cation demands that we find a new way of living. We need sustainability solutions
that acknowledge this fact and research communities that are responsive to it.
[1] For instance, consider the following statement issued by Monsanto: ‘The main
uses of GM crops are to make them insecticide- and herbicide tolerant. They don’t
inherently increase the yield. They protect the yield’. Quoted in E. Ritch, ‘Monsanto
Strikes Back at Germany, UCS’, Cleantech.com (April 17, 2009). Accessed on July
18, 2009.
[2] Especially important here are the effects of climate change, as well as the
‘superweed’ phenomenon of increasingly resistant pests that significantly diminish
yields.
[3] Productivist discourse invariably ignores Amartya Sen’s (1981, 154; Roberts
2008, 263; WFP 2009, 17) classic point that the volume and availability of food
alone is not a sufficient explanation for the persistence of world hunger. It is well
established that enough food exists to feed in excess of the world’s current popula-
tion (OECD 2009, 21)
[4] Although the calculations are complex and contested, one common estimate is
that industrial agriculture requires an average 10 calories of fossil fuels to produce a
single calorie of food (Manning 2004), which might rise to 40 calories in beef
(Pimentel 1997).
[5] Externalities of our current food system are often ignored or heavily
subsidised away. Moore (2015: 187) describes the situation as ‘a kind of “ecosystem
services” in reverse’: ‘Today, a billion pounds of pesticides and herbicides are used
each year in American agriculture. The long recognized health impacts have been
widely studied. Although the translation of such “externalities” into the register of
accumulation is imprecise, their scale is impressive, totalling nearly $17 billion in
unpaid costs for American agriculture in the early twenty-first century’. On exter-
nalities see: Tegtmeier and Duffy (2004).
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Part IV
Management and Marketing
Chapter 17
Insight into Risks in Aquatic Animal Health
in Aquaponics
17.1 Introduction
The European Food Safety Authority reported a variety of drivers and potential
issues associated with new trends in food production, and aquaponics was identified
as a new food production process/practice (Afonso et al. 2017). As a new food
production process, aquaponics can be defined as ‘the combination of animal
aquaculture and plant culture, through a microbial link and in a symbiotic relation-
ship’. In aquaponics, the basic approach is to get benefit from the complementary
functions of the organisms and nutrient recovery. The aquaculture part of the system
applies principles that are similar to recirculating aquaculture systems (RAS).
Aquaponics has gained momentum due to its superior features compared to tradi-
tional production systems. Thus, aquaponics seems capable of maintaining ecosys-
tems and strengthening capacity for adaptation to climate change, extreme weather,
drought, flooding and other disasters. These attributes are within reach, but as in
other agri-/aquacultural production, aquaponics is not free of risks. Given the
complexity of aquaponics as an environment for co-production of aquatic animals
with plants, the hazards and risks may be more complicated.
The focus in this chapter is on categories of risk (i.e. animal health/disease) rather
than specific risks (e.g. flectobacillosis disease). In traditional aquaculture, some of
the more common types of production risks are diseases resulting from pathogens,
unsuitable water quality and system failure. Snieszko (1974) reported that infectious
diseases of fish occur when susceptible fish are exposed to virulent pathogens under
certain environmental conditions. Thus, the interaction of pathogens, water quality
and fish resistance is linked to occurrence of disease. Previous research using risk
methods has studied the routes of introduction of aquatic animal pathogens in order
to secure safe trade (e.g. import risk analyses) and support biosecurity (Peeler and
Taylor 2011). Considering the similarity of aquaponics to RAS, it is expected that
the health problems of aquatic animals in aquaponics may be identical to aquatic
animals in RAS. Specifically, fluctuations in water quality may increase suscepti-
bility of fish to pathogens (i.e. disease-causing organisms such as virus, bacteria,
parasite, fungi) in RAS and cause disease outbreaks. Microorganisms in closed
systems such as RAS or aquaponics are of significance in terms of maintaining
fish health. Thus, Xue et al. (2017) reported the potential correlation between fish
diseases and environmental bacterial populations in RAS. High pathogen density
and limited medication possibilities make the system prone to disease problems.
Disease or impaired health can cause catastrophic losses with decreased survival or
poor feed conversion ratios. Regardless of which potential risk becomes problem-
atic, each has the same impact: an overall decline in the production of a marketable
quality product that then results in financial loss (McIntosh 2008). Diseases can be
prevented only when the risks are recognized and managed before disease occurs
(Nowak 2004). The severity of risks differs and will likely change depending on
when each is encountered during the production cycle.
17 Insight into Risks in Aquatic Animal Health in Aquaponics 437
Fish pathogens are prevalent in the aquatic environment, and fish are generally able
to resist them unless overloaded by the allostatic load (Yavuzcan Yıldız and Seçer
2017). Allostasis refers to the ‘stability through change’ proposed by Sterling and
Eyer (1988). Put simply this is the effort of fish to maintain homeostasis through
changes in physiology. Allostatic load of fish in aquaponics may be a challenging
factor as aquaponics is a complex system mainly in terms of the water quality and the
microbial community in the system. Hence, the diseases of fish are generally species-
and system-specific. Specific aquaponic diseases have not been described yet. From
aquaculture, it is known that fish diseases are difficult to detect and are usually the
end result of the interaction between various factors involving the environment,
nutritional status of the fish, the immune robustness of the fish, existence of an
infectious agent and/or poor husbandry and management practices. In order to
sustain aquaponic systems, an aquatic health management approach needs to be
developed considering the species cultured, the complexity of environments in
aquaponics and the type of the aquaponic system management. Profitability in
aquaponic production can be affected by even small percentage decreases in pro-
duction, as seen in aquaculture (Subasinghe 2005).
Aquaponics is a sustainable, innovative approach for future food production
systems, but this integrated system for production currently shows difficulties in
moving from the experimental stage or small-scale modules to large-scale produc-
tion. It could be hypothesized that the lack of economic success of this highly
sustainable production system is due to major bottlenecks not scientifically
addressed yet. Without a doubt, the cost-effectiveness and technical capabilities of
aquaponic systems need further research to realize a scaling up of production (Junge
et al. 2017). Research activity and innovations applied since the 1980s have
transformed aquaponic technology into a viable system of food production, and
although small-scale plants and research-structured plants are already viable,
commercial-scale aquaponics are not often economically viable. The claimed advan-
tages attributed and recognized for aquaponic systems are the following: significant
reduction in the usage of water (compared to traditional soil methods of growing
plants), bigger and healthier vegetables than when grown in soil, production of
plants does not require artificial fertilizer and aquaponic products are free of antibi-
otics, pesticides and herbicides.
Risk Communication
factors that could create large deviations between expected outcomes and the actual
outcomes (uncertainties, vulnerabilities). Risk analysis offers tools to judge risk and
assist in decision-making (Ahl et al. 1993; MacDiarmid 1997). Risk analysis is based
on systematic use of the available information for decision-making, using the
components of hazard identification, risk assessment, risk management and risk
communication as indicated by World Organisation of Animal Health (OIE)
(Fig. 17.1). This framework is commonly used for pathogen risk analysis (Peeler
et al. 2007).
Risk analysis in food production, including aquaponics, can be applied to many
cases, such as food security, invasive species, production profitability, trade and
investment, and for consumer preference for safe, high-quality products (Bondad-
Reantaso et al. 2005; Copp et al. 2016). The benefits of applying risk analysis in
aquaculture became more clearly linked to this sector’s sustainability, profitability
and efficiency, and this approach can also be effective for the aquaponics sector.
Therefore, disease introduction and potential transmission of pathogens can be
evaluated in the context of risk to aquatic animal health (Peeler et al. 2007). Various
international agreements, conventions and protocols cover human, animal and plant
health, aquaculture, wild fisheries and the general environment in the field of risk.
The most comprehensive and broad agreements and protocols are the World Trade
Organization’s (WTO) Sanitary and Phytosanitary Agreement, United Nations
Environmental Program’s (UNEP) Convention on Biological Diversity and the
supplementary agreement Cartagena Protocol on Biosafety and the Codex
Alimentarius (Mackenzie et al. 2003; Rivera-Torres 2003).
A key challenge regarding the field of risk relates to our depth of knowledge. Risk
decisions are related situations characterized by large uncertainties (Aven 2016).
Specifically, animal health risk analysis depends on knowledge gained from studies
of epidemiology and statistics. Oidtmann et al. (2013) point out that the main
constraint in developing risk-based surveillance (RBS) designs in the aquatic context
is the lack of published data to advance the design of RBS. Thus, to increase robust
17 Insight into Risks in Aquatic Animal Health in Aquaponics 439
Table 17.1 Composite research needs for aquatic animal health in aquaponics
Research area Research need
Basic research Understanding the aquatic animal health and welfare concept in aquaponics
in terms of the species of aquatic organisms and the system used
Understanding the stress/stressor concept for aquatic organisms in
aquaponics by the species and the system used
Understanding the allostatic load for aquatic organisms and the emergence of
diseases
Understanding the welfare concept in aquaponics
Characterizing the critical water quality parameters against aquatic animal
health
Understanding the sensitivity of aquatic organisms to the aquaponic
environment
Revealing the microbial profile for the different systems of the aquaponics
Health indicators Developing and validating health indicators for aquatic animals raised in the
aquaponic systems
Database Field data on the health/disease of aquatic animals in the aquaponics
development Field data on the microbial profile including pathogens
knowledge of risks in aquaponics, studies that both increase scientific data and
reduce specific weaknesses and uncertain fields in aquaponics operations are needed.
Some research areas that require more data for risk analysis in aquaponic systems are
presented below (Table 17.1).
In terms of risk analysis for aquatic animal diseases or health in aquaponic
systems, the OIE Aquatic Animal Health Code (the Aquatic Code) can be considered
because the Aquatic Code sets out standards for the improvement of aquatic animal
health and welfare of farmed fish worldwide and for safe international trade of
aquatic animals and their products. This Code also includes use of antimicrobial
agents in aquatic animals (OIE 2017).
Table 17.2 List of potential hazards for aquatic animal health in aquaponics
Hazard identification Hazard specification
Abiotic pH Too high/too low/rapid
change
Water temperature Too high/too low/rapid
change
Suspended solids Too high
Dissolved oxygen content Too low
Carbon dioxide content Too high
Ammonia content Too high, pH dependent
Nitrite content Too high
Nitrate content Extremely high
Metal content Too high, pH dependent
Biotic Stocking density Too high/too low
Biofouling
Feeding Nutrients by the fish species Surplus/deficiency
Feeding frequency Inadequate/improper
feeding
Dietary toxins
Feed additives Unsuitable growth
promoters
Management Aquaponic system design Poor system design
Fish species Unsuitable for aquaponics
Operational issues (water circulation, biofilter,
mechanical)
Chemotherapeutants use Threat for the microbial
balance
Staff hygiene
Biosecurity
Welfare Stressors Too high
Allostatic load High
Rearing conditions Suboptimal
Diseases Nutritional diseases
Environmental diseases
Infectious diseases
micronutrients (Fe+2, Mn+2, Cu+2, B+3 and Mo+6), normally scarce in water where
fish are reared, is essential to adequately sustain crop production. In comparison to
hydroponic culture, crops in aquaponic systems require lower levels of total
dissolved solid (TDS, 200–400 ppm) or EC (0.3–0.6 mmhos/cm) and require, like
fish, a high level of dissolved oxygen in water (Rakocy et al. 2006) for root
respiration.
While fish diseases caused by bacteria, viruses, parasites or fungi can have a
significant negative impact on aquaculture (Kabata 1985), the appearance of a
disease in aquaponic systems can be even more devastating. Maintenance of fish
health in aquaponic systems is more difficult than in RAS, and, in fact, control of fish
diseases is one of the main challenges for successful aquaponics (Sirakov et al.
2016). Diseases which affect fish can be divided into two categories: infectious and
non-infectious fish diseases. Infectious diseases are caused by different microbial
pathogens transmitted either from the environment or from other fish. Pathogens can
be transmitted between the fish (horizontal transmission) or vertically, by (externally
or internally) infected eggs or infected milt. More than half of the infectious disease
outbreaks in aquaculture (54.9%) are caused by bacteria, followed by viruses,
parasites and fungi (McLoughlin and Graham 2007). Often, although clinical signs
or lesions are not present, fish can carry pathogens in a subclinical or carrier state
(Winton 2002). Fish diseases can be caused by ubiquitous bacteria, present in any
water containing organic enrichment. Under certain conditions, bacteria quickly
become opportunistic pathogens. The presence of low numbers of parasites on the
gills or skin usually does not lead to significant health problems. The capability of a
pathogen to cause clinical disease depends on the interrelationship of six major
components related to fish and the environment in which they live (physiological
status, host, husbandry, environment, nutrition and pathogen). If any of the compo-
nents is weak, it will affect the health status of the fish (Plumb and Hanson 2011).
Non-infectious diseases are usually related to environmental factors, inadequate
nutrition or genetic defects (Parker 2012). Successful fish health management is
accomplished through disease prevention, reduction of infectious disease incidence
and reduction of disease severity when it occurs. Avoidance of contact between the
susceptible fish and a pathogen should be a critical goal, in order to prevent outbreak
of infectious disease.
Three main measures to achieve this goal are:
• Use of pathogen-free water supply.
• Use of certified pathogen-free stocks.
• Strict attention to sanitation (Winton 2002).
17 Insight into Risks in Aquatic Animal Health in Aquaponics 443
• Avoid high stocking density, which causes stress and may increase the incidence
of disease even if other environmental factors are acceptable. Also, high stocking
density increases the possibility of skin lesions, which are sites of various
pathogen entries into the organism.
• Regularly remove contaminants from water (uneaten food, faeces and other
particulate organics). Dead or dying fish should be removed promptly as they
can serve as potential disease sources to the remaining stock and a breeding
ground for others, as well as fouling the water when decomposing (Sitj-
à-Bobadilla and Oidtmann 2017).
• Disinfect all equipment used for tank cleaning and fish manipulation. After
adequate disinfection, all equipment should be rinsed with clear water. Use of
footbaths and hand washing with disinfecting soap at the entrance and within the
buildings are recommended. These steps directly decrease the potential for the
spread of pathogens (Sitjà-Bobadilla and Oidtmann 2017). Certain chemicals
used as disinfectants (such as benzalkonium chloride, chloramine B and T,
iodophors) are effective for disease prevention.
• Administer dietary additives and immunostimulants for improvement of health
and to reduce the impacts of disease. Such diets contain various ingredients
important for improvement of health and disease resistance (Anderson 1992;
Tacchi et al. 2011). There exists a wide range of products and molecules,
including natural plant products, immunostimulants, vitamins, microorganisms,
organic acids, essential oils, prebiotics, probiotics, synbiotics, nucleotides, vita-
mins, etc. (Austin and Austin 2016; Koshio 2016; Martin and Król 2017).
• Segregate fish by age and species for disease prevention, since susceptibility to
certain pathogens varies with age, and certain pathogens are specific to some fish
species. Generally, young fish are more susceptible to pathogens than older fish
(Plumb and Hanson 2011).
Maintaining the health of fish in aquaponics requires adequate health manage-
ment and continuous attention. Optimal fish health is best achieved through
biosecurity measures, adequate production technology and husbandry management
practices which enable optimal conditions. As mentioned, avoidance through opti-
mal rearing conditions and biosecurity procedures are the best way to avoid fish
diseases. Invariably, however, a pathogen may appear in the system. The first and
most important action is to identify the pathogen correctly.
Examination of live fish starts by observing their behaviour. Constant and careful
daily observation enables early recognition of diseased fish. As a rule, fish should be
observed for behavioural changes before, during and after feeding.
Healthy fish exhibit fast, energetic swimming movements and a strong appetite.
They swim in normal, species-specific patterns and have intact skin without discol-
orations (Somerville et al. 2014). Diseased fish exhibit various behavioural changes
with or without visible change in physical appearance. The most obvious indicator of
deteriorating fish health is the reduction (cessation) of feeding activity, usually as a
result of an environmental stress and/or an infectious/parasitic disease. The most
obvious sign of disease is the presence of dead or dying animals (Parker 2012;
Plumb and Hanson 2011).
Behavioural changes in diseased fish may include abnormal swimming (swim-
ming near the surface, along the tank sides, crowding at the water inlet, whirling,
twisting, darting, swimming upside down), flashing, scratching on the bottom or
sides of the tank, unusually slow movement, loss of equilibrium, weakness, hanging
listlessly below the surface, lying on the bottom and gasping at the water surface
(sign of low oxygen level) or not reacting to external stimuli. In addition to
behavioural changes, diseased fish exhibit physical signs that can be seen by the
unaided eye. These gross signs can be external, internal or both and may include loss
of body mass; distended abdomen or dropsy; spinal deformation; darkening or
lightening of the skin; increased mucus production; discoloured areas on the body;
skin erosions, ulcers or sores; fin damage; scale loss; cysts; tumours; swelling on the
body or gills; haemorrhages, especially on the head and isthmus, in the eyes and at
the base of fins; and bulging eyes (pop-eye, exophthalmia) or endophthalmia
(sunken eyes). The internal signs are changes in the size, colour and texture of the
organs or tissues, accumulation of fluids in the body cavities and presence of
pathological formations such as tumours, cysts, haematomas and necrotic lesions
(Noga 2010; Parker 2012; Plumb and Hanson 2011; Winton 2002).
Upon suspicion of deteriorating fish health, the first step is to check water quality
(water temperature, dissolved oxygen, pH, levels of ammonia, nitrite and nitrate) and
promptly respond to any deviations from the optimal range. If the majority of fish in
the tank has abnormal behaviour and shows non-specific signs of disease, there is
likely a change in the environmental conditions (Parker 2012; Somerville et al.
2014). Low oxygen (hypoxia) is a frequent cause of fish mortality. Fish in water
with low oxygen are lethargic, congregate near the water surface, gasp for air and
have brighter pigmentation. Dying fish exhibit agonal respiration, with mouth open
and opercula flared. These signs are also evident in fish carcasses. High ammonia
levels cause hyperexcitability with muscular spasms, cessation of feeding and death.
Chronic deviation from optimal levels results in anaemia and decreased growth and
disease resistance. Nitrite-poisoned fish have behavioural changes characteristic of
hypoxia with pale tan or brown gills and brown blood (Noga 2010).
When only few fish show signs of disease, it is imperative to remove them
immediately in order to stop and prevent the spread of the disease agent to the
446 H. Yavuzcan Yildiz et al.
other fish. In the early stages of a disease outbreak, generally only a few fish will
show signs and die. In the following days, there will be a gradual increase in the daily
mortality rate. The diseased fish must be carefully examined in order to determine
the cause. Only a few fish diseases produce pathognomonic (specific to a given
disease) behavioural and physical signs. Nevertheless, careful observation will often
allow the examiner to narrow down the cause to environmental conditions or disease
agents. In a serious disease outbreak, a fish veterinarian/health specialist should be
contacted immediately for professional diagnosis and disease management options.
In order to solve the disease problem, the diagnostician will need a detailed descrip-
tion of the behavioural and physical signs exhibited by the diseased fish, daily
records of the water quality parameters, origin of the fish, date and size of fish at
stocking, feeding rate, growth rate and daily mortality (Parker 2012; Plumb and
Hanson 2011; Somerville et al. 2014).
Treatment options for diseased fish in an aquaponic system are very limited. As both
fish and plants share the same water loop, medications used for disease treatments
can easily harm or destroy the plants, and some may get absorbed by the plants,
causing withdrawal periods or even making them unusable for consumption. The
medications can also have detrimental effects on the beneficial bacteria in the
system. If a medicinal treatment is absolutely necessary, it must be implemented
early in the course of the disease. The diseased fish is transferred into a separate
(hospital, quarantine) tank isolated from the system for treatment. When returning
the fish after the treatment, it is important not to transfer the used medications into
the aquaponic system. All these limitations require improvements of disease man-
agement options with minimal negative effects to the fish, the plants and the system
(Goddek et al. 2015, 2016; Somerville et al. 2014; Yavuzcan Yildiz et al. 2017). One
of the most used and effective, old-school treatments against the most common
bacterial, fungal and parasitic infections in fish is a salt (sodium chloride) bath. Salt
is beneficial for the fish, but can be detrimental to the plants in the system (Rakocy
2012), and the whole treatment procedure must be performed in a separate tank. A
good option is to separate the recirculating aquaculture unit from the hydroponic unit
(decoupled aquaponic systems) (see Chap. 8). Decoupling allows for fish disease
and water treatment options that are not possible in coupled systems (Monsees et al.
2017) (see Chap. 7). One recent improvement for the control of fish ectoparasites and
disinfection in the aquaponic systems is the use of Wofasteril (KeslaPharmaWolfen
GMBH, Bitterfeld-Wolfen, Germany), a peracetic acid-containing product that
leaves no residues in the system (Sirakov et al. 2016). Alternatively, hydrogen
peroxide can be used, but at a much higher concentration. While these chemicals
have minimal side effects, their presence is undesirable in aquaponic systems and
alternative approaches, such as biological control methods, are required (Rakocy
2012).
17 Insight into Risks in Aquatic Animal Health in Aquaponics 447
The biological control method (biocontrol) is based on the use of other living
organisms in the system, relying on natural relationships among the species (com-
mensalism, predation, antagonism, etc.) (Sitjà-Bobadilla and Oidtmann 2017) to
control fish pathogens. At present, this method is a complementary fish health
management tool with high potential, especially in aquaponic systems. The most
successful implementation of biocontrol in fish culture is the use of cleaner fish
against sea lice (skin parasites) in salmon farms. It is best practiced in Norwegian
farms where cleaning wrasse (Labridae) are co-cultured with salmon. The wrasse
remove and feed on sea lice (Skiftesvik et al. 2013). Although cleaning is less
common in freshwater fish, the leopard plecos (Glyptoperichthys gibbiceps),
cohabiting with blue tilapia (Oreochromis aureus), successfully keeps infection
with Ichthyophthirius multifiliis under control by feeding on the parasite cysts
(Picón-Camacho et al. 2012). This biocontrol method is becoming increasingly
important in aquaculture and can be considered in aquaponic systems. Additionally,
it must be noted that the cleaner fish can also harbour pathogens that can be
transmitted to the main cultured species. Therefore, they must also undergo preven-
tive and quarantine procedures before introduction into the system.
Another biocontrol method, still in the exploratory application phase in fish
culture, is the use of filter-feeding and filtering organisms. By reducing the pathogen
loads in the water, these organisms can lower the chances of disease emergence
(Sitjà-Bobadilla and Oidtmann 2017). For example, Othman et al. (2015) demon-
strated the ability of freshwater mussels (Pilsbryoconcha exilis) to reduce the
population of Streptococcus agalactiae in a laboratory-scale tilapia culture system.
The potential of this biocontrol method in aquaponic systems is yet to be tested, and
new studies are needed to explore the possibilities not only for fish disease control
but also for control of plant pathogens.
The most promising and well-documented biocontrol method is the use of
beneficial microorganisms as probiotics in fish feed or in the rearing water. Their
usage in aquaponic systems as promoters of fish/plant growth and health is well
known, and probiotics have also demonstrated effectiveness against a range of
bacterial pathogens in different fish species. For example, in rainbow trout, dietary
Carnobacterium maltaromaticum and C. divergens protected from Aeromonas
salmonicida and Yersinia ruckeri infections (Kim and Austin 2006) and Aeromonas
sobria GC2 incorporated into the feed successfully prevented clinical disease caused
by Lactococcus garvieae and Streptococcus iniae (Brunt and Austin 2005). Dietary
Micrococcus luteus reduced the mortalities from Aeromonas hydrophila infection
and enhanced the growth and health of Nile tilapia (Abd El-Rhman et al. 2009).
Recent research by Sirakov et al. (2016) has made good progress in simultaneous
biocontrol of parasitic fungi in both fish and plants in a closed recirculating
aquaponic system. In total, over 80% of the isolates (bacteria isolated from the
aquaponic system) were antagonistic to both fungi (Saprolegnia parasitica and
Pythium ultimum) in the in vitro tests. Bacteria were not classified taxonomically,
and the authors assumed that they belonged to the genus Pseudomonas and to a
group of lactic acid bacteria. These findings, although very promising, have yet to be
tested in an operational aquaponic system.
448 H. Yavuzcan Yildiz et al.
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Chapter 18
Commercial Aquaponics: A Long Road
Ahead
Authors Maja Turnšek and Rolf Morgenstern have equally contributed to this chapter.
M. Turnšek (*)
Faculty of Tourism, University of Maribor, Brežice, Slovenia
e-mail: maja.turnsek@um.si
R. Morgenstern · I. Schröter · M. Mergenthaler
Department of Agriculture, University of Applied Sciences of South Westphalia, Soest,
Germany
e-mail: morgenstern.rolf@fh-swf.de; schroeter.iris@fh-swf.de; mergenthaler.marcus@fh-swf.
de
S. Hüttel
Institute of Food and Resource Economics, Chair of Production Economics, Faculty of
Agriculture, Rheinische Friedrichs-Wilhelms Universität Bonn, Bonn, Germany
e-mail: S.Huettel@ilr.uni-bonn.de
M. Leyer
Institute of Business Administration, Rostock University, Rostock, Germany
e-mail: michael.leyer@uni-rostock.de
higher outputs per area might be achieved compared to conventional agriculture, yet
aquaponic systems might require more energy, capital and work input. Only refer-
ring to land as an input factor assumes that other production factors are not scarce,
which is hardly the case. Therefore, statements like the above neglect the “all other
things being equal” principle in economic assessments. Vaclav Smil (2008) calcu-
lates and summarises energy expenditure of different agricultural activities, utilising
energy as the common denominator, and this allows us to compare different agri-
cultural methods with the aquaponic approach.
A similar myth is contained in the statement: “A major advantage pertaining to
the aquaponics industry is that crop production time can be accelerated”
(IndustryARC 2012). An acceleration of crop production necessarily depends on
the amount of nutrients and water, oxygen and carbon dioxide in the surrounding
atmosphere and light and temperature available to crops – factors that are not
elements of aquaponics per se but can be added via greenhouse management
practices, such as fertilisation and irrigation heating and artificial lights. These
additional elements, however, increase both the costs of investment and the opera-
tional costs, often being too expensive to be economically viable (depending of
course on the location, type of crops and especially the price of crops).
Another economically important advantage of aquaponics provided in the report
was that “aquaponics is an adaptable process that allows for a diversification of
income streams. Crops may be produced depending upon local market interest and
the interest of the grower” (IndustryARC 2012). What statements like this gloss over
is the fact that diversification of production always comes at a price. Crop diversi-
fication necessarily includes higher levels of knowledge and higher labour demands.
The larger the variety of crops, the more difficult it is to meet optimum conditions for
all the selected crops. Large-scale commercial production thus looks for constant
parameters for a limited number of crops that need similar growth conditions,
allowing for large outputs in order to penetrate distribution via large distribution
partners such as supermarket chains, and allow for the same storage and potential
processing equipment and processes. Such large-scale production is able to use
economies of scale to reduce unit costs, a basic principle in economic assessment,
which is not usually the case for aquaponics at smaller scales of production.
Finally, the most important statement provided in the report was that “the return
of investment (ROI) for aquaponic systems ranges from 1 to 2 years depending on
the farmer experience as well as the scale of farming” (IndustryARC 2012). Such
statements need to be taken with extreme caution. The scarce data that is available
on return on investments reports on a much longer time: According to Adler et al.
(2000), it takes 7.5 years of return for an approximately $ 300.000 investment in
the hypothetical scenario of a rainbow trout and lettuce system. Recently,
Quagrainie et al. (2018) reported a similar period of 6.8 years for the payback of
an investment in aquaponics if the products can only be sold at non-organic prices.
Real data on the economics of aquaponics is extremely hard to come by, since the
enterprises that have ventured into commercial aquaponics are reluctant to share
their data. In cases where enterprises are performing well, they either do not share
456 M. Turnšek et al.
their data, since it is considered a business secret, or if they do share data, such data
needs to be taken with caution since typically these companies have an interest in
selling aquaponic equipment, engineering and consultancy. In addition,
enterprises that have failed in achieving profitability prefer not to publicly share
their failures.
These “myths” are continually circulating online amongst non-experienced
aquaponic enthusiasts, fuelled by hope for both high returns and a path towards
more sustainable future food production. So there is a need to go beyond the myths
and look at individual enterprises and provide an in-depth analysis on the basic and
the general economics of aquaponics.
Even if realistic data on aquaponics were available, it has to be considered that
such analyses are based on single cases. As aquaponic systems are far from techni-
cally standardised production systems, the diversity with respect to marketing
concepts is even higher. So, data on every single aquaponics system lacks
generalisability and can be regarded only as a single case study. General statements
are therefore not valid if the framework conditions and technical and marketing
specificities are not made transparent.
Journalistic publications about aquaponics often follow a narrative that elaborates
on the general challenges of global agriculture, such as shrinking agricultural areas,
humus loss and desertification, and then elaborate on the advantages of aquaponic
food production methods. Apart from the above-mentioned mistake that in fact
controlled environment system (CES) production is compared with field production,
no distinction between agriculture and horticulture is made. Whilst the term “agri-
culture” technically includes horticulture, agriculture in its more specific sense is the
large-scale crop production on farmland. Horticulture is the cultivation of plants,
usually excluding large-scale crop production on farmland, and is typically carried
out in greenhouses. Following these definitions, the plant side of aquaponics is
horticulture and not agriculture. Thus comparing yield and other productivity prop-
erties of aquaponics with agriculture is simply comparing apples to oranges.
To state this differently, the horticulture side of agriculture is only a very small
part of it. Large-scale crop production in agriculture mostly encompasses so-called
staple food production: Cereals like corn, barley and wheat, oilseed like rape and
sunflower and starchy root vegetables like potatoes. The agricultural area of Ger-
many covers 184.332 km2 (Destatis 2015). Of that only 2.290 km2 (1,3%) is used for
horticulture. Of the horticultural area, 9.84 km2 (0,0053%) is protected and under
glass. Absolute and relative figures for other countries surely differ, but the example
clearly shows that the plant side of aquaponics will only be able to substitute and
thereby enhance a small fraction of our food production. Staple foods can theoret-
ically be produced in CES under glass using hydroculture as demonstrated in NASA
research (Mackowiak et al. 1989) and could surely also be cultivated in aquaponic
systems, but due to the high investment needed for such production, it does not make
sense to think of aquaponics replacing the production of these crops under the
current global economic and resource conditions.
18 Commercial Aquaponics: A Long Road Ahead 457
With the continuous rise in the number of aquaponics growers, the first in-depth
analyses of the state of the art of the industry emerged, focused primarily on the
USA. These studies showed a less optimistic picture of the emerging industry. Love
et al. (2015) performed an international survey amongst 257 participants, who in the
last 12 months sold aquaponics-related food or non-food products and services. Only
37% of these participants could be named as solely commercial producers who
gained their revenue from selling only fish or plants. Thirty-six percent of the
respondents combined the sales of produce with aquaponics-related material or
services: Sale of supplies and equipment, consulting fees for design or construction
of aquaponics facilities and fees associated with workshops, classes, public speaking
or agro-tourism. Finally, approximately one third (27%) were organisations that sold
only aquaponics-related materials or services and no produce. The average
aquaponics production site of 143 US-based producers was 0,01 ha. By comparing
this to the overall hydroponic production in Florida (29,8 ha), Love et al. (2015)
concluded that the size of aquaponics producers is significantly smaller than hydro-
ponic production and is to a large extent still more of a hobby activity than successful
commercial enterprises. In terms of water volume, the aquaponics farms reported
comparable sizes as typical RAS aquaculture farms in the USA. Yet nearly a quarter
of respondents (24%) did not harvest any fish in the last 12 months, and the
estimated overall size of fish production was 86t of fish, which is less than 1% of
the farmed tilapia industry in the USA.
According to the same study, aquaponics was the primary source of income for
only 30% of respondents, and only 31% of respondents reported that their operation
was profitable in the last 12 months. For example, the median respondent received
only $1000 to $4999 in the last 12 months, and only 10% of respondents received
more than $50,000 in the last 12 months. This led Love et al. (2015) to conclude that
aquaponic farms were small-scale farms, which is comparable to agriculture in
general, since farms with gross revenues of less than $ 50,000 made up approxi-
mately 75% of all farms in the USA and farms with less than $50,000 typically sold
only around $7800 in local food sales – making it thus necessary to combine farming
income with other sources of income. It is therefore not surprising that aquaponics,
like small-scale farming, relies heavily on volunteer work. Typically, there were a
large number of unpaid workers, family members and volunteers working on these
small units, with an average of six unpaid workers per facility.
Similarly, Engle (2015) addresses the 2012 census where 71 aquaponics farms
across the USA were reported which represented 2% of all aquaculture farms. Of
these, only 11% had sales of $ 50,000 or more, compared to 60% of pond-based
aquaculture operations that had sales of $ 50,000 or more. Additionally, Engle
(2015) points out to the difficulties of obtaining data from these farms, for example,
estimating annual costs to operate in aquaponics farms, since many of these systems
are quite new.
In summary, from an economic point of view, there is a research gap in so far that
there are no records and analysis available which include statements about econom-
ically viable systems. Further research is needed that would take into account (a) the
production possibility curves (normative), (b) the combined analysis of fish and
18 Commercial Aquaponics: A Long Road Ahead 459
plants including feedback between both, (c) the economic efficiency in combination
with optimising the business processes and feedback (simultaneous optimization
production process and economic efficiency) and (d) the consideration of different
scales (scale efficiency) against the background of the environmental sustainability
of this agricultural system. In addition, there are no comprehensive and reliable data
that combine key factors such as production volumes, factor entitlements and cost
structures, scaling and sales strategies derived from existing real investments.
Further profitability analyses should consider temporal aspects and risk whilst
formulating normative benchmarks that in turn can serve as the basis for investment
decisions.
In Hawaii, Baker (2010) calculated the break-even price of aquaponics lettuce and
tilapia production based on a hypothetical operation. The study estimates that the
break-even price of lettuce is $3.30/kg and tilapia is $11.01/kg. Although his
conclusion is that this break-even can potentially be economically viable for Hawaii,
such break-even prices are much too high for most European contexts, especially
when marketing through retailers and conventional distribution channels. In the
Philippines, Bosma (2016) concluded that aquaponics can only be financially sus-
tainable if the producers manage to secure high-end niche markets for fish and large
markets for fresh organic vegetables.
Aquaponics on tropical islands (Virgin Islands and Hawaii) and warm, frost-free
zones (Australia) contrasts highly to locations further away from the equator. The
advantages in warm locations are the lower costs of heating and the seasonally even
availability of daylight, thus allowing for potentially low-cost systems to econom-
ically survive. A frost-free location close to the equator with little to no seasonal
differences makes it cheaper and easier to set up and operate a system year-round,
which allows for semi-professional family business setups in those regions. Addi-
tionally, local production in these areas is valued higher since leafy green crops are
either hard to store (e.g. Australia/heat) or difficult to transport to the customers
(Islands) and generally have a much higher contribution margin than in locations
such as Europe and Northern America.
Aquaponics can have several advantages in an urban context. Yet, advantages are
only effective if the specific urban framework conditions are taken into account and if
additional communication efforts are put in place. Peri-urban agroparks are presented
by Smeets (2010) as a technically and economically viable solution for urban agricul-
ture, offering synergy potential with existing industry through residual heat and
suitable logistics as well as alternative inorganic and organic materials streams, for
example, CO2, from cement production. Rooftop aquaponics utilises “empty” spaces
in urban areas (Orsini et al. 2017). Rooftops are often assumed to be free of cost
“because they are there”. Yet every space in the city is of high value. An owner of a
460 M. Turnšek et al.
building will always seek revenue for the space they offer, even the utilisation of
vacant rooftops. A rooftop farm carries a high economic risk and changes may have to
be made to the building (vents and logistics). Rooftops are also interesting for solar
energy production with less risk to the operator (see also Chap. 12).
Whilst aquaponics is often explicitly touted as a production technology suitable
for urban environments and even areas with contaminated soil, the real estate cost is
often completely underestimated. For example, official real estate prices in Germany
can be examined via the online tool BORISplus (2018), revealing a significant gap
between inner city limit prices and agricultural land prices. For example, peri-urban
real estate within city limits in Dortmund, Germany, is in the 280 €/m2–350 €/m2
range, whereas agricultural land outside of the city limits is in the 2 €/m2–6 €/m2
range. In addition to that German building codes grant the privilege to farmers to
erect agricultural buildings outside of the city limits. This legal and financial
situation renders agricultural land in proximity to economic zones attractive for
larger-scale aquaponic farms, leading to the above-mentioned concept of agroparks.
The placement of aquaponic farms raises challenges with customer perception.
Citizens who have been interviewed about their preference of different urban
agriculture concepts for inner city public land use showed a preference for usage
that keeps the space accessible for citizens as well as a low acceptance levels for
agroparks (Specht et al. 2016). The research results on the acceptance of aquaponics
revealed a larger variance than the other potential utilisations, suggesting a citizen
ambivalence due to a lack of information on the production method. Additional
communication efforts are required as aquaponics is a highly complex and new
production system unknown to most people in society including urban populations.
The potentials and risks of aquaponics in an urban context become clear from the
paragraph above. Distinct strategies and contingency plans have to be developed in
an urban context when planning to implement an aquaponics production facility.
Most of the data currently collected on commercial farmers is focused on
locations outside of Europe. A sound economic assessment of aquaponics facilities
in European latitudes and climates is difficult, because on the one hand only very few
commercial plants exist in Europe and on the other hand technical equipment, scale
and business models are very different in other parts of the globe, where commercial
aquaponics is more widespread (Bosma et al. 2017). Whilst Goddek et al. (2015) and
Thorarinsdottir (2015) provide a very good overview of European commercial plants
and their challenges, they present only a few economic parameters such as (targeted)
consumer prices, statements on “potentially” achievable income or break-even
prices for production. Since these are only valid under the specific conditions of
the investigated facilities, only limited statements can be transferred to other loca-
tions, even within Europe.
Whilst there are some specific assessments of productivity (e.g. Medina et al.
2015, Petrea et al. 2016), full market potential analysis and well-founded cost-
effectiveness assessments are not known at the present time. In addition, there are
initial studies on technical dynamic models using the methodology system dynamics
such as Goddek et al. (2016) and Körner and Holst (2017). This illustrates how
18 Commercial Aquaponics: A Long Road Ahead 461
(h) Labour cost has been calculated at minimum wage, which is a strong assumption
with regard to high levels of human capital required to run complex aquaponics
systems.
(i) Mortality losses of 5% in the aquaculture system are compensated by
overstocking at the start of each production cycle.
An analysis of the cost structure of the modelled production-sized aquaculture
system shows that labour, fish feed and juveniles and energy are the main cost
drivers, contributing roughly one third of the main costs each. At this point, it has to
be emphasised that labour costs are calculated on a minimum wage basis and that
costs for the occupied area of the farm have not been considered in the calculations
(Fig. 18.1).
Electricity and heating costs offer potential for optimization. Pumps have a
lifetime between 2 and 5 years. Inefficient pumps can be replaced with more efficient
pumps in the natural machine life cycle. Cost efficiency gains for these kinds of
optimizations are simple to calculate, and efficiency gains are also easy to monitor
after implementation. Similar measures to reduce heating costs are relatively easy to
calculate. For example, the costs and effects of additional insulation panels can be
calculated, and also here the gains can be easily monitored.
Labour costs emerge as the main cost driver that shows significant optimization
potential with upscaling. Larger-scale systems allow for the usage of labour-
8%
34% Labour Cost
34% 24% Fish Feed
12% 15% Juveniles
12% Electricity
8% Heating
3% Transportation
15% 2% Variable Machine Costs
24% 1,5% Other Variable Costs
1% Materials
0,5% Veterinary and Hygiene
0,1% Water
Fig. 18.1 Cost structure for aquaculture side of an aquaponics system, hypothetical model from
technical data from the pilot plant of the University of Applied Sciences of South Westphalia.
(Based on Morgenstern et al. 2017)
18 Commercial Aquaponics: A Long Road Ahead 463
4%
6%
33%
11%
Fig. 18.2 Cost structure for hydroponics side of an aquaponics system, hypothetical model from
technical data from the pilot plant of the University of Applied Sciences of South Westphalia.
(Based on Morgenstern et al. 2017)
464 M. Turnšek et al.
The analysis additionally sheds light on the job creation potential of the respective
systems. The model calculation was performed under the assumption that all the
required overhead tasks of the enterprise are handled by regular employees, an
assumption that is rather optimistic with regard to the fact that the minimum wage
has been used for the calculation.
One further assumption was made regarding the separation of jobs: The
employees work on both parts of the sytem, the aquaculture and the
hydroculture parts, in accordance to the work that is needed by the respective system.
This requires an elevated skill set which puts another question mark behind the
minimum wage calculation.
Even in the larger-sized production system, the number of jobs created is limited.
The calculated number of jobs is congruent with experience from horticultural
companies working with hydroponics, which usually employ between five and ten
workers per hectare of greenhouse (Table 18.2).
Data on initial investments in aquaponics is on the one hand very difficult to come
by and on the other hand even more difficult to compare. Some of the preliminary data
collected from other sources on the initial investment needed to set up an aquaponics
farm (see Table 18.3) below shows high differences between the initial investments in
the systems, either real or in hypothetical modelling. Since the systems differ in the
extreme amount of factors, it is highly problematic to draw any conclusions regarding
the necessary initial investments. However, the initial investment in aquaponics does
seem to be relatively high, which is reflective of the early stage of the industry. We
estimate that an initial investment in a commercial aquaponics system in Europe starts
18 Commercial Aquaponics: A Long Road Ahead 465
with at least 250 EUR / m2 of growth area but can easily require a much higher
investment, depending on the outside conditions, the system size and complexity and
the length of the growth season aspired to (Table 18.3).
The experimental and pioneering status of commercial aquaponics is one reason
why the financing of larger commercial-scale projects can be a challenge. Most
aquaponic systems have been financed through research grants or through
aquaponics enthusiasts. Personal communication with German banks that are tradi-
tionally strong in financing agricultural investments and that are therefore familiar
with the intricacies of crop production and animal rearing revealed that they would
not finance an aquaponics project due to lack of a proven and established business
model (Morgenstern et al. 2017).
Within the COST FA1305 project, three European pilot aquaponic systems opened
their doors for site visits of COST members:
– Ponika, Slovenia, Matej Leskovec (site visit made on 23 March 2016).
– UrbanFarmers AG, system in the Netherlands, Andreas Graber (site visit made on
6 September 2016).
– Tilamur, Spain, Mariano Vidal (site visit made on 20 April 2017).
Within the site visits, we asked questions about the type and size of the system,
the initial investment, the types of fish and crops produced and the reasoning behind
it and the selling experiences.
18.4.2 Presentations
The comparison shows a wide span of economic value ranging from 5.70€/m2/
cycle (baby leaf spinach) up to 2110€/m2/cycle (basil) and 23.00€/m2/cycle (mint).
Realistically, these figures should not be taken as reference points for upscaled
commercial productions, but they illustrate how different the economic output of
the crop production can be. Table 8 of the publication elaborates on the seasonal
market price variability of the examined crops. The seasonal variations of these
crops are rather moderate with slightly elevated prices in fall and winter months.
Seasonal market price variations for produce and fruit with higher global market
volumes like tomatoes and strawberries are usually much more pronounced, enticing
producers to put effort into season extension at both ends. Artificial lighting for
season extension is costly both investment-wise and regarding operational cost but
might well be worthwhile, especially considering the inherent pressure to utilise
process water from the aquaculture in the low light season.
No emphasis has been placed on product quality and marketability of the pro-
duced biomass within this study. Experience shows that the cultivation of certain
crops is easier than the cultivation of others. Mint is generally regarded as an easy-to-
grow crop, whilst the production of marketable basil is more challenging. Petrea
et al. (2016) cultivated the crops in deepwater culture and ebb and flow grow beds
with LECA substrate. The latter is particularly uncommon in commercial produc-
tion, since it has close to zero potential for rationalisation and automation. Basil
usually is produced in pot culture as opposed to a cut and come again production of
mint which leaves the rootstock in the system with a faster regrowth of a marketable
product. In addition to the different growth medium requirements, different crops are
produced with differing temperatures, climate and light regimes. Optimal product
quality can only be achieved with optimal cultivation techniques. It is important to
remember that customers are used to premium quality and show little to zero
tolerance for suboptimal products.
The horticulture side of commercial aquaponics faces high risks from infesta-
tions of diseases or parasites, which can be difficult to overcome because only
biological controls can be used (see Chaps. 14 & 17). Large risks are involved also
since most aquaponic farms require a market that will pay higher-than-average
prices for the crop. Finally, aquaponics seems to be very labour-intensive since
even small scale aquaponics systems are complex because of their many compo-
nents and requirements (Engle 2015).
For start-ups, it might be tempting to strive for the production of a wide spectrum
of novelty varieties of plant species with fruity aromas or colourful leaves. Melon
sage (Salvia elegans) or pineapple mint (Mentha suaveolens ‘Variegata’) are exam-
ples for these kinds of varieties. According to small-scale commercial producers in
Soest, Germany (non-aquaponics; personal communication summer 2016), the
market demand for novelty varieties has long been recognised by retailers and is
being supplied for by their large-scale producers. This segment is not a profitable
niche any more but rather a market that follows yearly trends. The switch by the
Berlin-based aquaponics producer ECF from a wide spectrum of the aforementioned
plant species in their start-up phase to a basil monocrop that is being marketed
through the German retailer REWE reflects this situation.
470 M. Turnšek et al.
Christian Echternacht from ECF, Berlin, reported in the interview about the
difficulty to sustainably establish a local direct marketing channel for a wider
range of products of limited quantity. Drawing from their first-hand experience,
the company decided to shift the plant-side production to one crop, basil in pots, and
to market this crop via one single retailer in over 250 supermarkets in the city of
Berlin. Interestingly the regionally labelled product (Hauptstadtbasilikum/Capital
City Basil) without an organic label is placed directly next to organically labelled
basil from non-regional sources and is reported to generate higher sales despite
slightly higher prices.
NerBreen based in Spain with its 6000 m2 size is currently the largest system in
Europe. It is more focused on the aquaculture element and includes aquaponics as
one of several means of water filtration, but the plant production is still 3000 m2 and
produces enough to create a market. They are currently undergoing the second
season of production within the farm, having 5 years previous experiences with a
smaller pilot plant (overall size of the pilot farm, 500 m2). In the winter season, they
now grow fresh garlic, strawberry plants without fruit (since the plants need to be
maintained for 3 years) and four different types of lettuce. In the summer, they
replace the garlic with cherry tomatoes and peppers but keep the strawberries and the
same lettuce varieties. Since this is only the second season, it is very difficult for
them to provide an average amount of produce. The last winter was very cold, and it
significantly affected the growth of the lettuce. In the first season, when they were
still trying to improve and gain experience, they produced about 3t of strawberries, 5t
of tomatoes and 60,000 lettuce heads. Their hopes are to ramp up production, whilst
at the same time, their strategy shifted from putting a focus on the quantity to quality
and variety instead. In the first year of their production, they had a good season with
tomatoes in terms of quantity – but the overall market was flooded with tomatoes,
and the price was subsequently too low. They adjusted to this problem with a focus
on more selected, niche varieties of cherry tomatoes since the price is better, and they
do not to want to compete with quantity but with quality, thus trying to reach a higher
price with the retailers.
Locally produced crops and niche cultivars seem to be the main directions for
crop selection in the European countries. The Slovenian company Ponika set out to
sell fresh-cut herbs in their 400m2-sized system since providing niche products in the
Slovenian market with no other local producer of fresh-cut herbs. The company
based their rationale on three main reasons. The first was that the data available,
albeit scarce, from US aquaponics farms showed that fresh-cut herbs seemed to be
the crops that succeed well in aquaponics and gained a higher price in the market.
The second was the years of positive experience within the small-scale DIY
aquaponics garden with these crops. In addition, the third was the positive feedback
received from fresh-cut herbs distributors in Slovenia regarding the interest in the
crops. The company set out to produce fresh-cut herbs and managed to sell them to
Slovenian gastro-distributors for two seasons, narrowing the initial number of crops
from six to three: fresh-cut chives, basil and mint. Other fresh-cut herbs they tested
proved to be either too sensitive, or there was too small and infrequent demand on
the market. The plan was to first sell the fresh-cut herbs to the gastro-distributors and
18 Commercial Aquaponics: A Long Road Ahead 471
then gradually proceed to selling these to large-scale retail chains. The reality,
however, showed significantly large risks in the production (e.g. powdery mildew
with basil and yellow tips with chives) and too small a system to be able to secure a
steady uninterrupted production as requested by the large-scale distribution chains.
Although the margins would be higher, Ponika never started to sell to the retail
chains since the contracts with large retail chains included financial penalties in the
case where the farm could not deliver the orders. Additionally, the retail chains made
weekly orders thus not allowing for appropriate planning, and in some cases, the
excess that was not sold had to be collected by the farmer, and this discarded produce
was expected to be deducted from the overall order even though the over-ordering
was on the side of the retailer.
The main reasons for the Slovenian-based company Ponika to stop their operation
were the combination of high risks accruing from the labour needed to cut, screen
and package the produce combined with the average gained price of 8 EUR / kg of
fresh-cut herbs (packaged in 100 g bundles) not providing enough of an economic
return to cover the extra workload. Since the company was the only Slovenian
company in the Slovenian market, the gastro-distributers were willing to take their
produce over the imported produce – yet only if the prices were equal to what the
prices of international competitors were on the market. With a high percentage of
fresh-cut herbs sold in the European market being delivered from North Africa, the
high extent of labour costs for aquaponically produced fresh-cut herbs meant that a
small-scale system could not compete with the prices as set by the extensive fresh-
cut herbs farms in warmer regions with lower labour costs, even when including
transportation costs. This shows that even when there is a niche in a local market,
there are often specific reasons for local producers not filling the niche. In the case of
fresh-cut herbs in Slovenia, this was the high cost of labour for too small a
niche market.
(Excursion Graber 2016 and Interview Echternacht 2018), putting the sustainability
claims of aquaponics in question. Christian Echternacht from ECF reports that the
contribution margin of the aquaculture has been overestimated in early calculations,
rendering the oversizing of the aquaculture part of the farm counterproductive for the
overall profitability of the farm.
Numerous different fish species have been reported to be produced in commercial
aquaponics in Europe. Popular species for aquaponics production are tilapia, African
catfish, largemouth bass, jade perch, carp and trout. There is no known commercial
aquaponics farm currently rearing European catfish, but researchers at the University
of Applied Sciences of South Westphalia (Morgenstern et al. 2017) found this
species to be suitable for aquaponics production. The selection of fish species is
influenced by a large number of different project-specific parameters. Most impor-
tantly of course are the market needs, price and distribution options. Within Europe,
coastal regions have a traditionally strong market for marine fish with a diverse set of
species and products. This creates a marketing challenge for freshwater aquaculture
production. Ivo Haenen from Uit je Eigen Stad, Rotterdam, and Ragnheidur
Thorarinsdottir from Samraekt Laugarmyri, Iceland, talked about this effect in
their interviews. Rotterdam customers are used to a rich and diverse supply of
marine fish products, making it difficult to market freshwater tilapia and African
catfish. The marine wild catch tradition is so ingrained into Icelandic culture that the
aquaculture aspect of aquaponics is probably not going to be actively promoted in
future aquaponics projects.
Tilapia, one of the most commonly used fish species in aquaponics in the USA
(Love et al. 2015), is a fish species that is not commonly known in Europe. As the
experiences from NerBreen in Spain show, European tilapia aquaponics producers
face a double marketing challenge: Their marketing attention needs to be put not
only towards building customer awareness on the benefits of aquaponics production
but also on the benefits of this relatively unknown fish species.
The suitability of the selected species for elevated water temperatures is another
important factor. Fish are poikilothermic; thus their growth and consequently their
production yields speed up with higher water temperatures. But elevated water
temperatures require more energy, which, depending on the selected energy source
for heating the process water, is connected with higher operational costs. Therefore,
the positive effect of higher yields has to be balanced with the elevated costs for
heating the water. From this perspective, it is desirable to tap into the potential of
residual heat usage from adjacently located power plants or industries. These
locations, however attractive and sensible they may be from an economical and
ecological point of view, might pose a challenge for the overall marketing of the
farm and its products. Industry sites are usually not idyllic and emotionally attrac-
tive, and worse still in case of anaerobic sewage plants or similar industries, they
might even appear to be repulsive. Consequently, the available locations, and the
context the farm can reasonably be placed in, is one factor for species selection.
The influence the different fish species have on plant yield and quality has not yet
been completely researched. Knaus and Palm (2017) conducted experiments com-
paring plant yield in two identical aquaponics systems with identical operating
18 Commercial Aquaponics: A Long Road Ahead 473
parameters rearing tilapia and carp and found that plant performance with tilapia was
better than with carp. These results show that there is indeed a difference in fish-plant
interaction, but these have not been researched for a wider range of different species.
In addition, the potential for fish polyculture, where two or more different fish
species are reared in the same aquaculture cycle, has not yet been systematically
researched.
One of the important operational factors for the fish selection is juvenile avail-
ability. Most of the commercial aquaponics producers buy juveniles from hatcheries.
One notable exception is the company Aqua4C in Belgium that produces jade perch
juveniles and uses these fish in their aquaponics system. A common recommendation
is to select a species with at least two known suppliers with significantly larger
capacity than the projected demand for the aquaponics farm. The rationale behind
this recommendation is risk mitigation. If the supplier of juveniles experiences
production issues and cannot deliver, the whole aquaponics production is in jeopardy.
As with the horticulture side of aquaponics, similarly the aquaculture part of
aquaponics faces high technical risks, such as the death of the fish due to electricity
outages, as reported by both Ponika from Slovenia and NerBreen in Spain. Ivo
Haenen, former operator of the aquaponics system of the Urban Farm “Uit je Eigen
Stad” in Rotterdam, reports that the heating system of the initial system setup was
not dimensioned appropriately. An unexpected period of cold weather led to lower
than tolerable process water temperatures resulting in losses in the aquaculture part
of the operation. These kinds of instances have to be attributed to the pioneering
character of early commercial aquaponics operations in Europe. The presented cases
illustrate why Lohrberg and his team classified aquaponics in the “experimental”
category of the seven identified business models of urban agriculture (Lohrberg et al.
2016).
The future of aquaponics production depends on public perception and the associ-
ated social acceptance in important stakeholder groups (Pakseresht et al. 2017). In
addition to potential aquaponics plant operators, players at the wholesale and retail
level as well as gastro-distributors and collective catering are important actors in
supply chains. Moreover, consumers are key actors as they bring in the money into
the supply chain at its end. Even though they have no direct economic stakes in
aquaponics production, the general public as well as political and administrative
bodies are important aspects to consider. The necessity of involving the aforemen-
tioned stakeholders is based on studies such as Vogt et al. (2016), who show that
suitable framework conditions are an important basis for the establishment of
innovative processes in food value chains. Technical developments without involv-
ing stakeholders run the risk of non-acceptance at the end of the research and
development pipeline. In general, they build on a comprehensive understanding of
a marketing philosophy with a multi-stakeholder approach.
474 M. Turnšek et al.
For aquaponics, there is still no knowledge about the conditions that promote the
dissemination of this technology. Although the technology used in aquaponics
installations for freshwater fish farming in tanks is also used in aquaculture, until
now this is unknown to a large part of society (Miličić et al. 2017). With regard to
consuming plants from aquaponics, there is scepticism regarding their contact with
fish water (Miličić et al. 2017). Preliminary studies based on a small sample
regarding the acceptance of aquaponics products by potential consumers indicate
that the requirements for products from aquaponics facilities go far beyond what the
previous purchasing behaviour of fish products suggests (Schröter et al. 2017c).
Based on the results of Schröter et al. (2017a), first hints on the effect of information
on the acceptance process are available. These need to be further explored by means
of perceptual and impact analyses of various information and presentation variants
(e.g. textual facts, images, word-image content) and validation on the basis of
representative samples. In addition, previous research has focused on citizens in
general and on potential consumers. Studies on the acceptance of other important
stakeholders such as potential plant operators, food retailers and public catering as
well as political and regulatory actors and the general public are lacking completely.
First analyses of the consumers’ response on aquaponics indicate that consumers
showed a positive attitude towards aquaponics, with food safety issues being the
major consumer concern in Canada (Savidov and Brooks 2004). Initial preliminary
work on the willingness to pay for fish products from aquaponics was carried out by
Mergenthaler and Lorleberg (2016) in Germany and Schröter et al. (2017a, b) on the
basis of non-representative samples in Germany. Part of these studies show a
relatively high willingness to pay for fish products from aquaponics. However,
these results are based on small samples and cannot be generalised because the
willingness to pay has been compiled from a specialist target group (see Mergen-
thaler and Lorleberg 2016) or in connection with the visit to a greenhouse for tropical
and subtropical plants grown using aquaponics (Schröter et al. 2017a, b).
According to Tamin et al. (2015), aquaponics products are green products. A
product is defined as green when it includes significant improvements in relation to
the environment compared to a conventional product in terms of the production
process, consumption and disposal (Peattie 1992). Based on the “theory of planned
behaviour (TPB)”, consumer acceptance of aquaponics products as innovative green
products has been examined by Tamin et al. (2015) with closed-ended question-
naires in Malaysia. From a set of different behaviour-influencing factors (relative
advantage, compatibility, subjective norm, perceived knowledge, self-efficacy and
trust), two factors have been identified as having a significant impact: Relative
advantage and perceived knowledge. The relative advantage describes how far
buying behaviour is influenced by superior product qualities compared to conven-
tional products. The aquaponics products were perceived fresh and healthy, and this
perception led to a buying advantage. The perceived knowledge relates to how much
the customer knows about the production method. The more the customers were
familiar with the method, the more likely they were willing to buy aquaponics
18 Commercial Aquaponics: A Long Road Ahead 475
products. There was no correlation in the category subjective norm, which relates to
how much the buying decision is influenced by the opinion of friends and family.
Interestingly there was no correlation for the factor of compatibility. This factor
relates to how much the product buying experience is compatible with the customer
lifestyle. It seems as if the product to market process in Malaysia is not very different
for aquaponics products and conventional products. So while it is questionable
whether the results of this study can be safely transferred to European markets, a
base message is that education about the production method and communicating the
beneficial effects regarding the freshness of the food and the benefits for the
environment are important marketing activities (Tamin et al. 2015).
Zugravu et al. (2016) surveyed the purchase of aquaponics products in Romania.
Customers were influenced by friends and family. This dimension, subjective norm,
showed no correlation in the Malaysian survey. The survey finds that consumers
have a general good overall image of aquaponics. They think that the products are
good for their health and that they are fresh. The paper describes a discrepancy
between the perception of fish from aquaculture and wild catch and the perception of
aquaculture. Retailers think that farmed fish can have a negative image, but actually
aquaculture itself does not really have a pronounced image. The lack thereof is
perceived by retailers as a marketing risk, yet it is described in the paper as giving the
potential for positive branding through targeted communication. As a recommenda-
tion, the paper concludes that the retailers should build on the trust that the con-
sumers showed when purchasing these fish products and should label the
aquaculture fish as “healthy and fresh” (Zugravu et al. 2016).
Interestingly both Tamin and Zugravu had a significant higher questionnaire
return count from women (Tamin et al. 2015; Zugravu et al. 2016). This raises the
question about gender differences in aquaponics marketing. Although quantitative
studies include gender as an independent variable in their analyses, no systematic
and consistent patterns have been found yet. This asks for more research explicitly
addressing gender aspects.
According to Echternacht from ECF in Germany, whose main business model is
to set up aquaponics systems, marketing is the component that is usually most
underestimated by their potential clients. ECF Farmsystems builds on this experi-
ence and surveys their potential customers for their intended marketing and distri-
bution goals. If they have an existing business with actual production and established
marketing channels, then the customer is very interesting. Idealistic customers who
think that the products are going to market themselves are treated with caution.
Depending on the intended target group, different scales of production units
might be favourable. Whilst some consumer segments prefer small-scale production
possibly linked to short transportation distances and local production, there might be
other consumer segments more interested in resource efficiency and low-cost pro-
duction which can be realised in rather large-scale production units linked to waste
energy and waste heat sources. Results from Rostock show (Palm et al. 2018) that
small-scale systems with simple technology can make sense. Medium-scale systems
476 M. Turnšek et al.
require all the maintenance and the operational expenses of larger-scale systems, but
do not have the benefit and output of large-scale systems. Conclusions from their
experience show that you should either go small and achieve high prices in local
markets or go to larger-scale systems with respective exploitation of economies of
scale allowing for price reductions. Bioaqua from the UK is one of the rare European
aquaponics companies that decided to follow the path of small-scale production with
simpler and cheaper systems and providing the added value via catering and finding
niche products for direct distribution to restaurants.
There might be other consumer segments displaying high preferences for fish
welfare who therefore have to be targeted with fish from production units that
conform to these ideals. As Miličić et al. (2017) show, consumers can express
unexpected aversions, such as vegans expressing highly negative attitudes towards
aquaponics. As pointed out in the literature, some facets of aquaponics may arouse
high emotional involvement, such as the aesthetics of the aquaponics system (Pol-
lard et al. 2017), level of mechanisation (Specht et al. 2016), soilless crop production
(Specht und Sanyé-Mengual 2017), fish welfare (Korn et al. 2014), concerns about
health risks due to the water recirculation system (Specht und Sanyé-Mengual 2017),
or negative emotions bordering on disgust, because fish excrement is used as
fertiliser for vegetables (Miličić et al. 2017). In this context, the perception and
evaluation of aquaponics and its products may be based on unconscious processes
rather than on careful consideration of logical arguments.
For some consumer segments, plants from aquaponics are innovative and inter-
esting, and for others the link between fish and plant production might not be
acceptable. This is also shown by ECF in Berlin: ECF decided to modify their initial
production and marketing strategy. In the beginning, they attempted to produce a
wide range of crops and market them directly on location. Nevertheless, according to
Christian Echternacht (Interview Feb 2018) the marketing effort is simply too large.
From their experience, the customers do not want to visit too many locations with
only a few products at each location. Therefore, ECF decided to produce only one
crop, basil, that is being marketed through a supermarket chain. Their experience as
well as more comprehensive literature reviews shows that depending on the degree
of meeting customer expectations, different levels of willingness to pay can be
achieved and therefore achievable market prices are highly context specific.
Similarly, Slovenian-based company Ponika first attempted direct distribution of
their fresh-cut herbs to restaurants in Ljubljana. But, just as with individual cus-
tomers, restaurants were also averse to direct ordering even if the price was lower.
For the restaurant managers, the time and effort needed to order individual products
was much too high a price to pay, and they were not willing to order directly. They
preferred to stay within their own gastro-distributors, whereby they could make their
overall purchase in just one order.
The experiences of ECF from Berlin and Ponika from Slovenia described above
are in line with previous experiences in the marketing of organic food products. To
sell these products locally through direct distribution will only be possible for a small
part of the products. Even though many consumers want to buy local and/or organic
18 Commercial Aquaponics: A Long Road Ahead 477
products, they often want to make their purchases as conveniently as possible. This
means that shopping has to be efficient in order to fit into their daily schedule. As
shown by Hjelmar (2011) for organic products, the availability of these food
products is important for consumers because most of the consumers are pragmatic.
They do not want to go to several stores in order to get what they want. They want to
buy their products conveniently in a nearby supermarket and if the supermarket does
not have a wide selection of organic products, many consumers end up by buying
conventional products (Chryssohoidis and Krystallis 2005). Similar experiences can
be described for consumers buying regional products in Germany (Schuetz et al.
2018). The same will presumably apply to aquaponics-grown products. If these
products will not be available in supermarkets, aquaponics will probably remain
niche production.
Organic food shoppers constitute a special potential target group of aquaponics.
Indoor production of vegetables might require less or no pesticide applications, but
soilless cultivation of plants is not an option in today’s legislation on organic
agriculture (cf. Chap. 19 of this book). Therefore, aquaponics in its strictest sense
will not provide the necessary characteristics to be eligible for certification as organic
production and no organic labels would be allowed on aquaponics products. There-
fore, either policymakers have to be lobbied to induce changes in organic legislation,
or organic shoppers have to be educated in this rather complicated issue. This aspect
is also important in the regard that organic classified products usually achieve higher
market prices than conventional products, and such certification would make the
aquaponics systems more economically viable. If aquaponics-grown products can be
sold at the same prices as organic products, under certain conditions, the payback
period of aquaponics systems can be reduced by less than half (Quagrainie et al.
2018).
Besides product marketing, services surrounding aquaponics production can
generate additional income streams. The high level of innovativeness of aquaponics
generates high levels of interest, which can be exploited in different service offers
which included paid-for aquaponics visits, workshops and consultancy services
around the establishment of new aquaponics systems. There are several examples
of aquaponics facilities venturing in this direction:
• ECF provides business consultancy for the establishment of new aquaponics
systems.
• UrbanFarmers, Den Hague, offered paid visits to the facility as well as an event
location. (Note: The project has now ceased).
Besides adjusting production systems to customer expectations in a comprehen-
sive marketing concept, communication strategies also play a role. Up to now,
knowledge about aquaponics in the society is weak (Miličić et al. 2017; Pollard
et al. 2017). When acquiring information, different variants of information and of
information representation will significantly influence the public perception of this
innovative technology. To satisfy the stakeholders’ information demands, different
channels of communication and different information materials can be used.
478 M. Turnšek et al.
Diversification strategies are required that include workshops, visitor guides and
other services. There are opportunities for new and alternative business ideas.
Examples of innovative communication approaches by some commercial
aquaponics operators show the specific challenges associated with aquaponics:
1. ECF, Berlin: Choosing red variety of tilapia. Branding as “Rosébarsch” at the
beginning of sales. Inspired by a customer’s branding in a restaurant, ECF
rebranded to “Hauptstadtbarsch” (capital city perch) in the meantime (Interview
Echternacht 2018). Thereby regional branding is put in the foreground of com-
munication rather than the inherent product quality oriented at the colour of the
fish meat.
2. Aqua4C, Belgium: They introduced jade perch from Oceania into the European
market. Aqua4C developed a branding as “Omega Baars” thus taking a novel
food approach. They implicitly market the regionally unknown fish species as
healthy while carefully avoiding to make any health claims.
3. Ponika, Slovenia: Marketing of produce from aquaponics has been difficult.
The situation was complicated as the aquaponics farm was located far away
from the market which was too far for a quick visit and also no other attraction
was nearby. They concluded that without the possibility of visits, it would be
difficult to secure the farm additional revenue sources or marketing directly to
consumers. In their marketing approach, they thus first targeted gastro-
distributors with a focus on quality and local production for a competitive
price. They did not dare to target individual consumers via supermarket chains
due to having too small of a system and subsequent inability to secure a steady,
large enough volumes of production. Thus they sold fresh-cut herbs directly to
gastro-distributors, whereby the price and local production played the most
important role. Their experience showed that gastro-distributors liked the story
of innovative food production and they liked helping young people in their
start-up business. So they were supportive in the sense that they adopted their
purchasing process by taking up the produce when it was available and ordering
from foreign sellers when it was not. In general, however, they were not very
interested in the sustainability character of aquaponics – in other words, they
did not care how the fresh-cut herbs were produced but rather that they were
locally produced and had appealing packaging (1 kg and 1/2 kg) where the local
character of the production was emphasised. Thus in their experience with
retailers, a company story of young innovators worked the best. Customers at
the retail level furthermore did not like the connection with hydroponics as they
mixed aquaponics and hydroponics. In Slovenia, the customers are wary of
hydroponics, and the Ponika company needed to tackle the challenge of chang-
ing the consumer’s perception from hydroponics, which has a negative image as
being “unnatural”, into aquaponics and create a positive image of aquaponics.
Additionally, the selection of fresh-cut herbs for the individual consumers
proved to be problematic, since the health benefits were not important enough
in fresh-cut herbs as people just do not eat that much of those to care enough
about, for example, pesticide-free production.
18 Commercial Aquaponics: A Long Road Ahead 479
this needs high time, as well as financial and creative inputs. It has to be acknowl-
edged that the reported high prices for aquaponics products only come at consider-
able costs of brand establishment. As any economic viability of aquaponic systems
will critically depend on achievable prices, more research is needed to understand
the different determinants of the customers’ willingness to pay for aquaponics
products.
Location decisions for aquaponics farming are a key determinant of economic
viability as many production factors related to aquaponics production are not flexible
in terms of space. This relates particularly to land. Aquaponics as a land-efficient
production system can only count on this advantage in land-scarce regions. Com-
paratively, rural areas with relatively low land prices therefore cannot generate
sufficient incentives unless there are other site-specific advantages, for example,
waste energy supply from biogas plants. Though being land-efficient in general,
aquaponics in urban contexts still competes for highly limited land resources. In
functional markets, land would be allocated to those activities with the highest
profits per unit of land and it is highly questionable if aquaponics will be able to
compete with very efficient industrial or service-oriented activities in urban contexts.
Therefore, aquaponics seems to fit only in urban areas that provide aquaponics with a
competitive advantage over competing potential activities.
Extending the definition of aquaponics and including aquaponics farming as
introduced by Palm et al. (2018) might align aquaponics much closer to traditional
economic farming analyses. This wider definition of aquaponics refers to process
water that is used for fertilisation combined with irrigation on fields. With this wider
interpretation of aquaponics, it becomes possible to produce staple foods in
aquaponic production systems. Since the nutrient absorption capacity of the agricul-
tural area might be limited in some regions, this definition implicitly positions
aquaponics as a competitor to pig, beef and poultry production. Since aquaculture
uses less resources than pigs, beef and poultry with respect to the final output, this
could become a viable option.
In traditional economic farm analyses, there is a strong technological and con-
ceptual separation of animal and plant production. With less technological interac-
tion in aquaponics farming as compared to aquaponics in its stricter senses, there will
also be less complex economic evaluation as the two systems of fish and plant
production can be modelled separately. To link the systems economically, system
internal prices would have to be determined, e.g. prices for nutrients brought from
fish production to fields of plant production.
Another issue is the prices obtained for final products from aquaponics farming.
Evidence on achievable prices from such kind of production systems are completely
lacking thus restricting reliable estimations on the economic viability as yet. With a
stronger separation of fish and plant production, it might be feasible to use prices for
conventional aquaculture products and conventional prices from plant production.
This would assume that there is no price premium for aquaponics farming. To test
whether this really is the case, price experiments combined with different commu-
nication tools have to be implemented.
482 M. Turnšek et al.
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Chapter 19
Aquaponics: The Ugly Duckling in Organic
Regulation
Abstract Due to the cyclic or systemic nature of both aquaponics and organic
production, organic certification appears to be a natural step for a researcher, system
designer or commercial-oriented aquaponics producer to engage in. However, the
underlying principles and justifications of aquaponics and organic production differ
considerably between respectively a technological- and a soil-based understanding
of nutrient cycles and long-term sustainability in food production. These principles
are confirmed in both the organic regulation regime of the EU and USA, and
presently leave the question ambiguously open as to whether aquaponics as a food
production system can be recognized and certified as organic. Despite an openness in
the organic regulation for new knowledge, adaptations and innovations, the organic
sector itself has shown a reluctance to recognize more knowledge-based intensive
speciality crops and technologies. This is particularly difficult with respect to small
organic sub-sectors such as horticulture and aquaculture production. Both are very
specific subsystems of the agricultural sector, where aquaponics potentially would
belong at the intersection between organic greenhouse horticulture and organic
aquaculture. Organically certified aquaponics would therefore need to establish a
niche within the organic sector. So in order to move forward, there is a great need for
a more serious but open-minded exchange and discussion among the aquaponics and
organic sub-sectors themselves to explore the potential but also limitations of their
respective production models. However, between the two food production systems,
there should be room for debate with a view to finding new and feasible roles for
aquaponics in the organic community.
P. R. Kledal (*)
Institute of Global Food & Farming, Hellerup, Denmark
e-mail: paul@igff.dk
B. König
Faculty of Life Sciences, Thaer-Institute, Horticultural Economics and IRI THESys, Humboldt
Universität zu Berlin, Berlin, Germany
D. Matulić
Department of Fisheries, Beekeeping, Game management and Special Zoology, Faculty of
Agriculture, University of Zagreb, Zagreb, Croatia
e-mail: dmatulic@agr.hr
19.1 Introduction
RAS Hydroponics
Discharge
RAS Hydroponics
Discharge
Fig. 19.1 (a) coupled (b) decoupled aquaponics system. (Adapted from Peterhans 2015)
In the EU, the present regulatory framework for organic fish and horticultural
production is regulated by the Council Regulation (EC) No. 834/2007, whereas
more detailed rules are regulated by the Commission Regulations (EC) No.
889/2008 and (EC) no. 710/2009. However, the EU organic regulatory regime
does not have any standards or regulations for certifying aquaponics as organic.
The organic regulation is based on the aims and principles of recognizing organic
farming as a natural resource-based food production (Lockeretz 2007; Aeberhardt
and Rist 2008). This is backed up in the implementing regulation annex by the
exclusion of inputs not allowed for organic farming. Consequently, aquaponics
farming systems using the RAS technology and soilless vegetable production
(hydroponics) cannot be certified as organic under the present EU organic
regulation.
However, among aquaponics practitioners, there is continuous discussion about
aquaponics and organic certification. First of all, the rapid industrial developments
within fish farming and the market diversification and demand for organic products
make it economically desirable to qualify for the organic price premium as one way
to reimburse the high capital investments required for commercial aquaponics.
Second, it appears only natural to link an environmental-friendly food production
such as aquaponics, to already well-established certification labels and consumer
perceptions of a sustainable food production rather than engaging in the high
transaction costs of creating a whole new food label.
In view of the current discussions on limited resources for food production,
animal welfare, the increasing pressure on the sustainability of the aquatic environ-
ment, paralleled with the ongoing technological progress within aquaponics, this
article asks why aquaponics cannot be certified organic.
In the following paragraph, the organic rules and regulations under the EU regime
creating barriers to aquaponics will be examined.
492 P. R. Kledal et al.
889/2008 Article. (4): Organic farming is based on nourishing the plants primarily through
the soil ecosystem. Therefore hydroponic cultivation, where plants grow with their roots in
an inert medium feed with soluble minerals and nutrients, should not be allowed.
Since aquaponics is based on using fish sludge as a source of fertilizing the plants,
the absence of mineral fertilizers would at first seem like a step towards organic
production. However, the ‘classical’ aquaponics production systems started using
components from the soilless hydroponic technology, and therefore the plants
produced under such a system cannot be certified as organic. In order to understand
this prohibition in organic regulation, it is helpful to remember that hydroponics was
developed and adopted by growers as a response to the challenges greenhouse
growers met in intensive soil-based vegetable cultivation systems, e.g. enrichment
of the soil with soil-borne pathogens. In contrast, the organic horticulture approach
departs from the question of how greenhouse farming has to look like in order to
avoid these challenges. Their starting point is instead to change the management of
the soil rather than inventing a production technology without soil.
In addition to this general principle of soil-based production, organic horticulture
can be considered a specialized niche within organic farming offering a considerable
variety of crops. The legislation for fruit vegetables, such as tomato, cucumber,
pepper, eggplant, etc. prescribes cultivation in natural soil. Plants sold with the soil,
such as seedlings or potted herbs, can be certified as organic. The prerequisite is that
the plant could continue growing at the customer’s greenhouse or kitchen window.
This means, that herb bunches, salads cut off from the roots need to be grown in soil
in order to qualify for organic certification. Inputs allowed for organic production are
regulated in the implementing regulation. For Germany, Switzerland and the Neth-
erlands, the testing and approval of inputs for organic production is maintained by
FiBL (Research Institute of Organic Agriculture), who are currently aiming at
developing a European List on inputs certified as suitable for organic status.
The nutrient supply in organic greenhouse production is a challenge. Not only are
mineral fertilizers common in hydroponic production systems not allowed but, in the
special case of the German organic farmer associations (going beyond EU legisla-
tion), also hydroxylates that are of animal origin (interview with organic extension
19 Aquaponics: The Ugly Duckling in Organic Regulation 493
service). Greenhouse growers who have invested in infrastructure sealing the natural
soil with permanent greenhouse flooring, have faced a long-time effective barrier for
the conversion of existing greenhouse infrastructure to organic farming schemes,
except for potted herbs (König 2004). New investments in greenhouse infrastructure
have contributed to the increase of organic fruit and vegetable production in the last
years, e.g. in Germany. However, for these modern organic growers, aquaponics
does not yet provide any solution as they are looking for answers into the areas of
suitable soils, improved crop rotation, effective microorganisms, compost and
the like.
Horticulture is facing the general challenge that the organic EU regulation is not
very detailed in this area. Theoretically, this leaves room for new production
approaches such as aquaponics. However, at this stage of development within both
commercial organic horticulture and aquaponics, the start-up costs for the producers
are immensely high let alone the search for information on production management,
prohibitions, potential yields, etc. In the end, the suitability of innovative production
systems is left to the decision of the local certification authority on a project-by-
project basis (König et al. 2018).
However, since the starting point in organic agriculture is about soil-based
production and the fact that horticulture, aquaculture and aquaponics are small
sub-sectors; the EU regulation regime on organic production may not be something
that is expected to change in the near future.
stocking density in organic aquaculture systems is often 1/4 to 1/3 of that in modern
RAS systems, and therefore from an economical aspect, not very cost-effective for
this technology. At the same time, we need research and development on animal
welfare indicators as well as on feasible and meaningful animal welfare monitoring
tools as a prerequisite to discussing specific stocking densities. Only then will we be
able to assess the potential economic viability of the aquaculture part of an organic
aquaponics system (Ashley 2007; Martins et al. 2012).
As in Europe, there is an ongoing discussion in the USA about how to handle soilless
or soil replacement approaches for nutrient provision to plants as a mean of a
resource-efficient food production and their inclusion or exclusion from the organic
certification scheme. Despite these discussions, the state of the art is somewhat
similar undecided to that in Europe, but practices differ: recently, the Crops Sub-
committee of the National Organic Standards Board provided a suggestion to make
aeroponics, aquaponics and hydroponics prohibited practices under Sect. 205.105 of
the USDA Organic Regulations (NOSB 2017). This decision was rejected with 8:7
votes, yet not achieving 10 votes to make the decision a recommendation of the
NOSB to USDA. Only the rejection of aeroponics found sufficient votes (14 out of
15, NOSB 2017). Therefore, the USDA Agricultural Marketing Service is only
reviewing the recommendation to exclude aeroponics from organic certification
(AMS 2018, p.2). This NOSB decision had been forced due to non-harmonized
practices in the past among accredited organic certification agencies, whereby some
of them certified hydroponics as organic under the National Organic Program (NOP)
while others did not. These differing practices can be seen as a result of a long
discussion process with no clear conclusions, ending with eight certifiers certifying
hydroponic operations as organic in 2010 and a 33% increase of organic certified
hydroponic producers (NOSB 2016: Hydroponic and aquaponics subcommittee
report). Already back in 2010, the NOSB had received recommendation for a federal
rule concerning greenhouse production systems, indicating basically that ‘Growing
media shall contain sufficient organic matter capable of supporting natural and
diverse soil ecology. For this reason, hydroponic and aeroponic systems are
prohibited.’, yet this explicit prohibition did not enter current law (NOSB 2010,
2016:122). Instead, the more open definition of organic production from 2002 was in
place, where organic production is ‘[a] production system that is managed in
accordance with the Act and regulations in this part to respond to site-specific
conditions by integrating cultural, biological, and mechanical practices that foster
cycling of resources, promote ecological balance, and conserve biodiversity’
(NOSB 2016, p. 7). The hydroponic and aquaponics subcommittee concludes that
‘Under current law and clarification from NOP/USDA, hydroponic and aquaponic
production methods are legally allowed for certification as USDA Organic as long
as the producer can demonstrate compliance with the USDA organic regulations.’
19 Aquaponics: The Ugly Duckling in Organic Regulation 495
(NOSB 2016, p. 10–11). However, the difficulty is that organic production is about
management of the soil, whereas hydroponics is a system managing fertilizers. By
not addressing this difference could lead to some ambiguity and potential negative
consequences for the support of organic certification by farmers and consumers
(AMS 2016). In the (NOSB 2016, Alternative Labeling Subcommittee Report),
other experts presented a range of ideas as to how labels within the USDA organic
scheme or outside could appear. Because of a lack of standards and norms, which is a
necessary basis for labels, the group did not arrive at a consensus. The opinion was
that, if aquaponics were included, or an extra label added, among the already existing
great diversity between the different organic productions systems, it would both
challenge the certification process as well as being a source of confusion for
consumers. Interestingly, the suggestions of label alternatives under the USDA
organic umbrella, or in addition to it, highlight the anecdotal evidence that the
principle of aquaponics farms seems to be appealing to consumers, and that they
do not need to be certified organic to be viable (NOSB 2016, Alternative Labeling
Subcommittee Report, p.5).
In summary, the NOSB (2016) provides a detailed process description from the
early 1990s until today, which reflects also different opinions of stakeholders
involved in this discussion. The Organic Foods Production Act of 1990 (OFPA)
builds on this basis for the development of federal US organic certification for the
NOSB, and since then the discussion about allowing greenhouse production systems
for organic certification or not has been in place (NOSB 2016). By now, there is
agreement in the discussion which recognizes that the roots of organic farming lie in
the concern about soil fertility and soil quality. All organic farming practices and
standards developed are based upon this premise, and any discussions about its
further development have to start from this point of view.
In the discussion, there are more open questions involved as to whether hydro-
ponics could be called organic or not. The comparison of conventional and organic
farming, in the case of horticultural greenhouse crops, hinges on some poorly
researched or still controversially discussed issues (NOSB 2017):
The type of farming practice may also explain the differences found in organic and
conventional products, e.g. lower content of secondary plant metabolites of
conventionally grown greenhouse vegetables compared to organic vegetables
from field farming. Allowing hydroponics to be certified as organic, this currently
communicated added value of organic products could not be communicated to
consumers anymore as added value unambiguously.
An important source of nutrients in hydroponic systems is hydrolysed soybean meal,
which US growers import from Europe in order to ensure GMO-free sourcing
compatible with organic standards. This impinges negatively upon the overall
sustainability.
One principle of organic farming is dealing with resilience, which is doubted for
hydroponic and aquaponics farming systems as they are highly dependent on an
external energy supply (anecdotal observations). Opponents state that organic
farms are likewise not ‘resilient’ against severe natural disasters, yet both groups
496 P. R. Kledal et al.
remain somewhat unclear about their resilience concept when applied to these
production systems.
A comparison of processes at the root surface, i.e. the microbial environment in soil
versus water and the nutrient uptake, is an open question and opponents argue
that literature on this topic is perceived as not sufficient.
In contrast, all the arguments that can be found in Europe as to why hydroponics
or aquaponics should be certified as organic are also brought into the discussion in
the US. The most remarkable point is, however, the lack of data on the direct
comparison of systems in order to be able to evaluate the mentioned impacts and
advantages systematically. In summary, the NOSB rejected to label hydroponic or
aquaponics systems as organic in general because (NOSB 2017, p. 70–71):
§ 6513 Organic Plan: “An organic plan shall contain provisions designed to foster soil
fertility, primarily through the management of the organic content of the soil through proper
tillage, crop rotation, and manuring...An organic plan shall not include any production or
handling practices that are inconsistent with this chapter.”
• § 205.200 General: “ Production practices implemented in accordance with this
subpart must maintain or improve the natural resources of the operation, including soil
and water quality.”
• § 205.203 Soil fertility and crop nutrient management practice standard: (a) “The
producer must select and implement tillage and cultivation practices that maintain or
improve the physical, chemical, and biological condition of soil and minimize soil erosion.”
(b) “The producer must manage crop nutrients and soil fertility through rotations, cover
crops, and the application of plant and animal materials.” (c) “The producer must manage
plant and animal materials to maintain or improve soil organic matter content...”
Later, in the year 2016, definitions were given for hydroponics, aquaponics and
aeroponics, stating for aquaponics that (NOSB 2017, p. 82):
Aquaponic production is a form of hydroponics in which plants get some or all of their
nutrients delivered in liquid form from fish waste. Aquaponics is defined here as a
recirculating hydroponic system in which plants are grown in nutrients originating from
aquatic animal waste water, which may include the use of bacteria to improve availability of
these nutrients to the plants. The plants improve the water quality by using the nutrients, and
the water is then recirculated back to the aquatic animals.
The NOP has strict standards for handling animal manure in terrestrial organic
production, but no such standards exist to ensure the safety of plant foods produced
in the faecal waste of aquatic vertebrates. Also, the NOP has not yet issued standards
for organic aquaculture production, upon which aquaponics plant production would
be dependent. ‘The Crops Subcommittee is opposed to allowing aquaponic produc-
tion systems to be certified organic at this time. If aquaculture standards are issued
in the future, and concerns about food safety are resolved, aquaponics could be
reconsidered.’ (NOSB 2017, p. 82).
In there is the ‘Naturally Grown’ certification, a peer-review, grassroot certifica-
tion, which explicitly includes aquaponics (https://www.cngfarming.org/
aquaponics). This certification involves a catalogue with criteria from January
2016. Only the vegetable produce is certified, not the fish part because at the moment
it (e.g. fish feed) does not meet the general criteria for livestock certification. The
19 Aquaponics: The Ugly Duckling in Organic Regulation 497
criteria regulate the following aspects: System Design and Components, Materials
for Main System Components and Growing Media/Root Support, Water Sources,
Monitoring, Inputs for pH Adjustment, Waste Use & Disposal, Crop Production and
Management, Fish Management, Location and Buffers, Energy and Record Keep-
ing. The scheme is based on peer inspection schemes and does not allow the usage of
synthetic pesticides and fungicides, copper-based pesticides, petrochemical-based
pesticides or fungicides. It does not regulate the components on the plant part, but
assesses its functions: water regulation, aeration, degassing, biofiltrations and
removal of fish waste solids.
In summary, there are individual organic certification bodies in the US certifying
aquaponics (parts) as organic production, but there are also cases reported of farmers
claiming organic production without being certified (Friendly Aquaponics 2018).
After this chapter goes to press there may be new developments affecting the organic
certification topic. In addition, the issue of urban farming being declared as farming,
and hence being eligible for agricultural funds might get a clearer status with the
pending new US Farm Bill.
This chapter has attempted to clarify the regulatory aspects relevant to understanding
why aquaponics presently is not eligible for organic certification in the EU and the
USA. As in the EU, the main paradigm behind organic farming in the USA is briefly,
to manage soils in a natural way. In the EU, organic certification decisions for
organic aquaponics are not carried out by local authorities, whereas the USA has
seen a growth in this type of action in the last few years as well as an increase in
private peer-review certifications and decisions of individual organic certification
agencies.
In principle, all EU organic regulations are open to adaptation as soon as there is
new scientific evidence, as stated in paragraph 24.
Parr. 24
Organic aquaculture is a relatively new field of organic production compared to organic
agriculture, where long experience exists at the farm level. Given consumers’ growing
interest in organic aquaculture products further growth in the conversion of aquaculture
units to organic production is likely. This will soon lead to increased experience and
technical knowledge. Moreover, planned research is expected to result in new knowledge
in particular on containment systems, the need of non- organic feed ingredients, or stocking
densities for certain species. New knowledge and technical development, which would lead
to an improvement in organic aquaculture, should be reflected in the production rules.
Therefore provision should be made to review the present legislation with a view to
modifying it where appropriate.
So, the horticultural, aquacultural and organic sectors would need to organize
themselves, integrating knowledge from different domains. Yet, there are difficulties
in convening such knowledge-intensive discussions as the experts and the
498 P. R. Kledal et al.
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the copyright holder.
Chapter 20
Regulatory Frameworks for Aquaponics
in the European Union
20.1 Introduction
T. Reinhardt (*)
GFA Consulting Group, Berlin, Germany
e-mail: tilman.reinhardt@gfa-group.de
K. Hoevenaars
AquaBioTech Group, Mosta, Malta
e-mail: kyh@aquabt.com
A. Joyce
Department of Marine Science, University of Gothenburg, Gothenburg, Sweden
e-mail: alyssa.joyce@gu.se
framework for aquaponics and gives some perspectives on how the development of
aquaponics could be supported through EU policy. It builds on the work by Koenig
et al. (2018) who have analyzed aquaponics through the theoretical framework for
emerging technological innovation systems (see Bergek et al. 2008) and have shown
how development pathways for this aquaponics might be influenced by institutional
conditions.
The first section provides an overview of specific regulations that govern each
step in development of aquaponic enterprises, i.e., construction, operation, and
commercialization. It analyzes how this regulatory framework provides incentives
or disincentives for individual entrepreneurs and market actors to invest in
aquaponics. The second section analyzes how aquaponics fits in with different EU
policies and how aquaponics can contribute to achieving EU sustainability goals. It
then shows how the policies and strategies need to be redefined in order to provide
better opportunities in this sector. In the third section, we draw conclusions from
lessons learned in the first sections in order to provide policy recommendations.
Note: The first section summarizes the findings of a legal guideline on the
feasibility of aquaponics projects in Germany. Detailed references to German reg-
ulations and case law have been left out for better readability. A German version
with references to specific provisions and relevant case law is available on request
from the authors. Parts of the second sub-chapter have been published in Eco cycles.
Reference: Hoevenaars, K., Junge, R., Bardocz, T., and Leskovec, M. 2018. EU
policies: New opportunities for aquaponics. Eco cycles 4(1): 10–15. DOI:
10.109040/ecocycles.v4il.87.
In this first section, our goal is to provide an overview of relevant regulations for the
construction and operation of aquaponics facilities and the marketing of
aquaponically produced products. We focus specifically on Germany, as it is impos-
sible to extrapolate across the EU given that several important regulations, especially
regarding zoning and construction, have not been harmonized across the
EU. Although we focus on the German context, similar findings regarding planning
law have also been reported in other countries (Joly et al. 2015).
Aquaponic facilities must comply with various planning, building and water regu-
lations, many of which do not fall under EU competence. In Germany, the general
framework for planning and water law is harmonized at the national level, while
building and local water-use regulations are determined at the state level, with urban
and regional planning covered at the municipal level.
20 Regulatory Frameworks for Aquaponics in the European Union 503
Planning law regulates the use of the soil and the area-related requirements for
construction projects. There is a major distinction between projects in outlying and
inner urban areas.
According to Section 35 of the German Building Code, outlying areas should be
kept free of buildings and are reserved for certain uses, such as agriculture or
renewable energy production. Whether or not aquaponics constitutes agriculture in
that sense remains an unanswered question: while courts have ruled that soilless
cultivation of vegetables such as hydroponics can be considered agriculture, the case
is less clear for aquaculture in indoor facilities with no connection to the natural
water cycle. The definition of agriculture in Section 201 of the Building Code only
recognizes fisheries. Most courts therefore view recirculatory aquaculture systems as
commercial rather than agricultural enterprises. Recently, however, the administra-
tive court of Hamburg has ruled that a plant for fish and crustacean production can be
considered agricultural, if the majority of the required feed could theoretically be
produced on the agricultural land, belonging to the farm regardless of the type of fish
produced, or whether feed is actually produced on the farm. This exception might
not be viable however in cases, where agriculturally sourced feed is not used at all. In
practice, aquaculture operations were often set up in connection with biogas plants.
As farmers received an additional bonus on the feed-in-tariff for cogenerating plants
(i.e. plants that also produce heat), there was an incentive to install heat-absorbing
aquaculture next to the biogas plant.
Additional restrictions may apply in protected areas. The construction of aqua-
culture facilities is seen as problematic especially adjacent to natural water bodies.
Exceptions for agriculture are only available for existing facilities. This has created a
number of problems in traditional fishery areas, such as Mecklenburg, where many
professional fishermen have an interest and necessary skills to operate ancillary
businesses such as aquaculture or aquaponics (Paetsch 2013). Given that aquaponic
systems do not rely on the natural water cycle, they could provide a creative
possibility for new enterprise if their benefits were assessed and recognized by
relevant authorities.
However, regardless of their size, aquaponics facilities do not require an envi-
ronmental impact assessment, which is only a requirement for fish farms that
discharge waste into surface waters.
the area where it is located. Commercial aquaponics farms can be classified as either
commercial or horticultural businesses. As such, they are generally not allowed in
residential areas. In villages and mixed-use areas, both commercial and horticultural
enterprises are allowed. In commercial and industrial areas, only commercial, but not
horticultural, businesses are possible.
As aquaponic facilities have comparatively few noise and odor issues, they may
be allowed on an exceptional basis even in areas where they are not currently
admissible under planning laws. However, obtaining an exception creates additional
administrative burdens and uncertainty, which could present an obstacle to scaling-
up of the technology. Project-specific planning allows for cooperation with planning
authorities but, in practice, is only relevant for large-scale projects due to the costs
involved.
Backyard aquaponics plants might be allowed in all zones under the exception for
ancillary facilities for keeping of small animals. However, ancillary facilities must
be noncommercial and are interpreted differently by different district authorities.
Some municipalities take a rather restrictive approach and only allow traditional
forms of small animals such as dogs, chicken, pigeons, etc.
Aquaponic systems do not necessarily depend on the use of surface water. Ideally
water leaves an aquaponic system only via evapotranspiration or as water retained in
the vegetables produced. We would argue that such facilities therefore should not
require a permit under the water act or wastewater regulations. This could provide a
20 Regulatory Frameworks for Aquaponics in the European Union 505
Fish farms present few problems in regard to noise and odor. One might therefore
assume that aquaponic systems could be permitted with more ease than other animal
production facilities. However, aquaponics does not fit well into the German legal
framework.
As aquaponic production does not depend on the use of soil, installations may not
be “agricultural enough” for outlying areas, i.e., agricultural lands. On the other
hand, aquaponics might be “too agricultural” for urban areas, as urban agriculture is
not considered a relevant category under German planning law. In particular,
aquaponics may be generally inadmissible in commercial, industrial, and residential
areas.
Commercial aquaponics facilities always require a building permit even if they
are installed in pre-existing buildings which themselves do not require new building
permits.
Aquaponics pioneers with very visible urban projects such as ECF or Urban
Farmers seem to have coped well with the existing regulatory framework. However,
planning law issues could present a relevant problem for scaling up the technology,
in which case projects need to be developed in close consultation with the authorities
in order to avoid future conflicts and to provide certainty for investors.
506 T. Reinhardt et al.
A major regulatory advantage of aquaponics may lie in the fact that little or no
wastewater is produced, thus reducing the need for wastewater removal. Wastewater
permits and fees have been reported to be significant obstacles for conventional fish
farmers. As wastewater fees will probably be calculated according to pollution
loading in the future, they may form an even stronger incentive to think about
alternative types of wastewater disposal in the future (Schendel 2016). However as
the water law generally does not provide for multiple uses, a legal clarification would
be very important to create certainty for producers.
Apart from this, regulatory conditions in the German water sector do not partic-
ularly favor innovation. German water law strictly adheres to the paradigm of
centralized sewage and generally does not allow for decentralized recycling of
material flows and other forms of “creative ecology.” Unlike in the waste sector,
where the regulatory framework has given strong incentives to the private sector to
consider waste as a resource, regulation of wastewater sector does not create
incentives for the private sector to create and implement innovative recycling
technologies.
Aquaponic production is subject to regulations for plant and for animal production at
all stages of production and processing. Under the regulatory approach “from farm to
fork,” many relevant regulations have been harmonized at the European level
(especially through the so-called EU hygiene package). However, a few exemptions
exist for small producers selling directly to customers.
20.2.2.2 Aquaculture
The most commonly cultivated fish in aquaponics systems are tropical species such
as tilapia or African catfish. However, the complex rules of Regulation (EC) 708/
2007 concerning the use of alien species in aquaculture generally do not apply to
closed recirculating aquaculture facilities (registered in a directory of recirculating
aquaculture facilities). Some countries (e.g., Spain and Portugal, but not Germany or
France), however, have decided to ban some types of exotic fish outright, which also
affects the possibilities of cultivating them in closed facilities.
All aquaculture producers are subject to German regulation on fish diseases, which
implements European Directive 2006/88/EC on animal health requirements for
aquaculture animals and products thereof and on the prevention and control of
certain diseases in aquatic animals (Ministry of Agriculture of Bavaria 2010).
Under this regulation, aquaculture operations generally require permits by the
local veterinary authorities. However, producers who only sell small quantities of
fish directly to consumers or to local retailers only need to register certain informa-
tion such as name and address, location and size of the operation, source of water
supply, amount of fish held, and fish species.
Most importantly, the regulation on fish diseases imposes a duty on operators of
fish farms to inform the local veterinary authorities in the event of a suspected
disease outbreak. Veterinary authorities may then implement necessary control
measures, which in some cases may involve destroying the entire stock should
there be concern of disease spread.
Note: European animal health law, which was previously regulated relatively
confusing in some 400 individual acts, is unified under Regulation (EU)
2016/429. However, the regulation only enters into force only on 21 April
2021. The content concerning fish diseases will not change (Art. 173 et seq.
Regulation (EU) 2016/429).
508 T. Reinhardt et al.
The ability to source sustainable animal feeds is a key prerequisite for sustainable
food production. In comparison to land animals, fish have a much better feed
conversion rate; however, many higher trophic-level fish species require a certain
portion of their feed to be derived from protein and fat from animal origin (e.g., fish
meal). Feeding insects or insect larvae to fish is often seen as a possible way to
increase the sustainability of aquaculture. Insects can be cultivated using waste
organic nutrients, in some cases derived from animal wastes, including offal.
Animals for human consumption however must not be fed proteins of animal
origin (with the exception of fish protein) according to Regulation (EC) 999/2001,
which was implemented in reaction to BSE crisis in the 1990s. While it is sometimes
argued that the ban of feed sources from animal protein should not apply to insects,
which were not considered as potential feed sources in 2001, the use of insect feed is
disallowed in practice by the German veterinary authorities.
Currently, some pet food is already produced using insect proteins (e.g., dog food
from Brandenburg-based start-up Tenetrio). Given the increased interest in using
insect protein for animal feed, several legislative changes have been made at the
European level to allow for the feeding of insect protein based on adaptations to the
existing regulatory frameworks (Smith and Pryor 2015). Since 2017, a so-called risk
profile of the European Food Safety Authority (EFSA) is available (EFSA Journal
2015; 13 (10): 4257). Insects may be allowed as feed in aquaculture from 2018.
However, some restrictions remain in place: in particular insects to be used as animal
feed must not have fed on human or ruminant waste products. Insect production also
poses some addition open regulatory questions, e.g., welfare issues regarding stan-
dard procedures for killing.
Compared to other livestock, there are far few animal welfare regulations (Chap. 17)
for handling and killing of fish. Although it is generally accepted that fish can feel
pain, there is a lack of scientific evidence to justify restrictions for animal welfare
(Studer/Kalkınç 2001). On the European level, there are only a few non-binding
recommendations initiated in 2006 by the European Commission. According to
Article 22 of these recommendations, a revised version based on new scientific
evidence was anticipated by 2011, but to date EFSA has only published species-
specific recommendations for certain types of fish, as well as special provisions on
the transport of fish. Article 25 lit f – h. and Annex XIII of Regulation (EC) 889/2008
on organic production and labeling of organic products also contains species-specific
rules on stocking density. As organic labeling is not available for fish from
recirculatory aquaculture (see below), these rules are not relevant for aquaponics.
Most private certification standards also do not consider animal welfare aspects
(Stamer 2009).
20 Regulatory Frameworks for Aquaponics in the European Union 509
Under Section 11 of the German law on animal welfare, keeping animals for
commercial purposes generally requires a permit. To obtain this permit, one must
demonstrate appropriate training or previous professional experience in animal
husbandry and show that the production system provides adequate nutritional and
housing facilities (Windstoßer 2011). Operations are considered commercial when
expected sales exceed € 2000 per year.
According to Section 11 para 1 no. 8 TierSchG, no permit is needed for the
commercial keeping of “farm animals.” Whether fish can be considered farm
animals in this sense is unclear. Exceptions to the animal welfare law are generally
interpreted strictly: species are only considered farm animals if the necessary skills
for keeping them can be acquired anytime, anywhere and there exists sufficient
experience regarding the keeping of a species (Windstoßer 2011). This may not be
the case for some types of tropical fish that differ fundamentally from native species
(e.g., Arapaima, whose use in aquaculture is currently being explored at IGB
Berlin).
The Administrative Court of Cologne has recently examined animal welfare
aspects when ruling on the admissibility of a so-called fish spa, where Kangal fish
were kept with the goal of using them to clean human feet. Operators of this fish spa
were able to prove through veterinary reports that animal welfare was not being
compromised and as such, a permit was granted.
allow stunning using the ice water method, which he was employing. Defining
appropriate killing methods for different fish species is the subject of an ongoing
research project funded by BLE at the University of Veterinary Medicine Hannover
and may lead to more restrictive regulations in the future.
Animal welfare aspects may also restrict certain forms of marketing and selling of
fish. For example, the Higher Administrative Court of Bremen has forbidden placing
farmed fish into ponds, from which were to be fished by recreational anglers as this
was considered “unnecessarily harmful.”
The German federal regulation on the vocational training of fish farmers does not
mention aquaponics. Some private companies offer courses on aquaponics on the
German market. However, it is not clear whether such courses are considered
sufficient to obtain necessary permits (e.g., for pesticide use, commercial keeping
of animals, slaughtering, etc.).
Hygiene law is harmonized on the European level through Regulations (EC) 852/
2004, 853/2004, and 854/2004.
As a general rule, all food business operators, regardless of product, have to
comply with EU hygiene law. As such, they must comply with the general standards
of hygiene and management in Annex I and II of Regulation 852/2004, including
basic requirements on production processes and personal hygiene, as well as appro-
priate waste treatment. They have to keep a register of the origin of animal feeds, as
well as the use of pesticides and veterinary drugs. Measures to avoid risks must be
documented in an appropriate manner.
According to Annex II Chapter IX no. 3 of Regulation (EC) 852/2004, food has to
be protected against any contamination at all stages of production, processing, and
distribution. Under Regulation (EC) No 178/2002, contamination may refer to any
biological, chemical, or physical agent in a food or a condition of a foodstuff, which
can cause adverse health effects. Food business operators must implement and
maintain a HACCP (hazard analysis and critical control points) system, which has
to be certified by accredited certification bodies. Details are agreed upon with local
authorities.
EU hygiene legislation does not apply to the direct supply of small quantities of
primary products to the final consumer or to local retail establishments. Small
amounts are defined as household amounts for direct delivery to consumers or for
local retail as for usual daily consumption. Primary production in the case of fish
includes catching, slaughtering, bleeding, heading, gutting, removing fins, refriger-
ation, and wrapping. Activities such as flash-freezing, filleting, vacuum packing, or
smoking will result in the fish no longer being considered primary local production.
20 Regulatory Frameworks for Aquaponics in the European Union 511
Under German law certain restrictions on food hygiene exist however even for direct
local food suppliers (Annex 1 LMHV).
Registration or authorization requirements in Regulation (EC) No 853/2004
depend on volume and type of processing. No registration or authorization is
required for the supply of primary products in household quantities directly at the
place of production, processing, or storage (including nearby markets). It is also
possible to supply retail establishments (supermarkets, restaurants), consumers, or
restaurants within a radius of 100 km. If primary products are delivered to end
consumers, or to restaurants in larger quantities, the company must register and
demonstrate their ability to meet food hygiene requirements. If more than one-third
of the animal-derived products are sold to retail outlets outside the region (radius of
100 km), a public health license is also required.
The legal requirements for aquaponic production are not higher than for the produc-
tion of fish or vegetables. However, the large number of applicable laws reflects the
complexity of aquaponics.
Compared to livestock farming, aquaculture may appear less regulated, especially
in the area of animal welfare law. However, legal “gray areas” and the corresponding
uncertainty are not always to the advantage of producers. Without established
administrative practices, there is a considerable risk of conflicts (c.f. for the cited
case in Switzerland, where an aquaculture operation was shut down, because the
producer was not allowed to kill the fish in specific ways). In addition, the large
number of applicable regulations can be burdensome, especially where European
and national regulations coexist (e.g., on animal welfare or hygiene). As there is no
harmonized law on aquaculture in Germany, producers need various permits from
different authorities. Authorities often have little experience with nontraditional
aquaculture, and as such, uncertain administrative requirements can be discouraging
for entrepreneurs. Given the relative newness of commercial aquaponics, potential
producers are strongly advised to contact local authorities at an early stage. In the
case of larger, commercial plants, operators should probably contact veterinary and
hygiene authorities prior to beginning construction.
The increasingly strict requirements of European hygiene laws can also constitute
a significant burden, especially for small enterprises who wish to market directly to
consumers or local restaurants (Schulz et al. 2013). However, whether exemptions
for direct sellers are of practical help to aquaponic operators remains to be deter-
mined. The few existing aquaponics facilities in Germany currently demonstrate the
necessity for producers to depend on a variety of sales channels and the need to
create various forms of ancillary revenue (guided tours, secondary processing,
cooking classes, etc.). Exemptions for direct selling therefore may become irrelevant
if hygiene standards have to be met for other reasons.
512 T. Reinhardt et al.
20.2.3 Commercialization
Rules on food labeling have largely been harmonized at the European level through
European Regulation 1169/2011 on food packaging. Besides the formal rules,
however, voluntary labeling standards play an even bigger role in the marketplace
(see Sodano et al. 2008). In the case of the EU organic label, the voluntary standard
is also regulated by law. In other cases, the rules of private certification schemes have
to be followed.
20 Regulatory Frameworks for Aquaponics in the European Union 513
The general rules for selling packaged products are laid down in European Regula-
tion 1169/2011 (e.g., the duty to include a list of ingredients, etc.). As a general rule,
Art. 7 para. 1 Regulation (EU) 1169/2011 bans misleading claims on food
packaging.
In addition to these general rules, Regulation (EU) 1379/2013 contains special
rules on consumer information regarding aquaculture products. For example, under
Art. 38 of Regulation (EU) 1379/2013, the member state or the third country, in
which the aquaculture product has acquired more than half of its final weight, must
be correctly named on the label.
Products from aquaponics are not eligible for labeling as organic under the current
EU regulations for organic products. Article 4, Regulation (EC) 889/2008, explicitly
forbids the use of hydroponics in organic farming. Recital 4 states that organic/
biological crop production is based on the principle that plants obtain their food
primarily from the soil ecosystem. For aquaculture products, Art. 25 g Regulation
(EC) 710/2009 forbids the use of closed-circuit systems, and according to Recital
11 of Regulation (EC) 710/2009, this follows from the principle that organic
production should be as close to nature as possible. These rules will not change in
the new EU organic labeling regulation adopted in 2018, which will enter into force
in 2021.
Laws preventing organic certification of hydroponic products are not shared by
countries such as the USA and Australia, where hydroponic/aquaponic products can
be certified organic.
In terms of business and tax law, there are various privileges that could theoretically
be exploited by aquaponics operators. Tax benefits could be especially interesting
for outside investors. However, it remains to be seen whether certain conditions
regarding the legal form of an enterprise and required investment volumes prevent
operators from claiming these benefits. So far, the best-known urban aquaponics
projects in Germany have not been profitable, so the issue of paying taxes has not
arisen.
Under business and tax laws, the thresholds for privileges of small-scale instal-
lations and direct marketers are not congruent with the thresholds under hygiene law.
A detailed review of operating and marketing concepts is therefore required in each
individual case.
The EU organic label is currently out of the question for aquaponic products.
However, there are increasingly private opportunities for certification.
National policies can only be analyzed for each individual country. We therefore
concentrate on relevant EU policies.
516 T. Reinhardt et al.
The Common Fisheries Policy (CFP) and the Common Agricultural Policy (CAP)
apply to the aquaculture and hydroponics components of aquaponics, respectively
(European Commission 2012, European Commission 2013). Policies on food safety,
animal health and welfare, plant health, and the environment (waste and water) also
apply.
The Rural Development Policy, also referred to as the second pillar of CAP, focuses
on increasing competitiveness and promoting innovation (Ragonnaud 2017). Each
member state has at least one rural development program. Most countries have set
goals to provide training, restructure and modernize existing farms, set up new
farms, and reduce emissions. Measures against excessive use of inorganic fertilizers
were introduced in the CAP as well as environmental policies and are regulated
through the EU’s Nitrates Directive (Directive 91/676/EEC 1991) and the Water
Framework Directive (WFD).
The CFP reform and strategic guidelines for the sustainable development of EU
aquaculture were issued by the Commission to assist EU countries and stakeholders
with challenges that the sector is facing. The emphasis is on facilitating implemen-
tation of the Water Framework Directive as it relates to aquaculture (European
Commission 2013).
The CFP requires the development of a multiannual national strategic plan in each
member state with strategies to promote and develop the aquaculture sector
(European Commission 2016). Taking into account their different histories and
cultivated species, each member state can support their existing aquaculture tech-
nologies but also develop new ones, such as aquaponics. This strategy should lead to
an increase in production and reductions in dependence on imports. The main
actions planned by member states are simplification of administrative procedures,
coordinated spatial planning, enhancement of competitiveness, and promotion of
research and development.
In the framework of the CFP, an Aquaculture Advisory Council (AAC) has been
established. The main objective of the AAC is to provide advice and recommenda-
tions to European institutions and member states on issues related to sustainable
development of the aquaculture sector (Sheil 2013).
A goal of both CFP and CAP is to increase competitiveness and sustainability of
aquaculture and agriculture, respectively (Massot 2017). One of the objectives in the
CFP is to exploit competitive advantage by obtaining high-quality, health, and
environmental production standards.
20 Regulatory Frameworks for Aquaponics in the European Union 517
The goal of the food safety policy of the EU is to ensure safe and nutritious food
from healthy animals and plants while supporting the food industry (European
Commission 2014). The integrated food safety policy also includes animal welfare
and plant health. In the strategy for animal welfare, there is an action on the welfare
of farmed fish; however, there are no specific rules in place (European Commission
2012).
Aquaponics is not only at the nexus of different technologies but also at the nexus of
different regulatory and policy fields. While it may provide solutions to various
sustainability goals, it seems to fall in the cracks between established legal and
political categories. To add to the complexity, the development of aquaponics is
affected by regulation from different levels of government. For example, facilitation
of urban agriculture has to come from the national or even subnational level, as the
EU has no competence in planning law. Major regulatory incentives for the imple-
mentation of aquaponic technology could probably be set in water law, which falls
under national and EU competence. Implementation of aquaponics could gain
significant traction, if aquaculture operations had the obligation or at least financial
incentives to deal with wastewater themselves. However this would require a major
change in the current regulatory approach.
In the theory on technological innovation systems (TIS), an “institutional align-
ment” in the formative phase of a TIS is seen as critical. Only if institutions are
sufficiently aligned will markets form and provide space for entrepreneurial
520 T. Reinhardt et al.
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Chapter 21
Aquaponics in the Built Environment
21.1 Introduction
Aquaponics has been recognized as one of “ten technologies which could change our
lives” by merit of its potential to revolutionize how we feed growing urban
populations (Van Woensel et al. 2015). This soilless recirculating growing system
has stimulated increasing academic research over the last few years and inspired
interest in members of the public as documented by a high ratio of Google to Google
Scholar search results in 2016 (Junge et al. 2017). For a long time, aquaponics has
been primarily practiced as a backyard hobby. It is now increasingly used commer-
cially due to strong consumer interest in organic, sustainable farming methods. A
survey conducted by the CITYFOOD team at the University of Washington in July
2018 shows that the number of commercial aquaponic operations has rapidly
increased over the last 6 years. This focused search for aquaponic operations
identified 142 active for-profit aquaponic operations in North America. Based on
online information, 94% of the farms have started their commercial-scale operation
since 2012; only nine commercial aquaponic farms have been in operation for more
than 6 years (Fig. 21.1).
Most of the surveyed aquaponic operations are located in rural areas and are often
connected to existing farms to take advantage of low land prices, available
Fig. 21.1 Existing aquaponic practitioners in North America, 142 commercial companies (red) and
17 research centers (blue), (CITYFOOD, July 2018)
21 Aquaponics in the Built Environment 525
Fig. 21.2 Aquaponics across Europe: 50 research centers (blue) and 45 commercial companies
(red). (EU Aquaponics Hub 2017)
that are affordable for an agricultural business (de Graaf 2012; De La Salle and
Holland 2010). Urban aquaponic farms need to balance higher production costs with
competitive marketing and distribution advantages that urban locations offer. The
largest benefit for locating aquaponic operations in cities is a growing consumer
market with an interest in fresh, high-quality and locally grown produce. When
complying with local regulations for organic produce, urban farms can achieve
premium prices for their aquaponically grown leafy greens, herbs, and tomatoes
(Quagrainie et al. 2018). Unlike hydroponics, aquaponics also has the capacity to
produce fish, further enhancing economic viability in an urban setting which often
has diverse dietary needs (König et al. 2016). Urban aquaponic farms can also save
some operational costs by reducing transportation distance to the consumer and
reducing the need for crop storage (dos Santos 2016).
Urban environmental conditions can also be advantageous for aquaponic farms.
Average temperatures in cities are higher than in rural surroundings (Stewart and
Oke 2010). In colder regions particularly, farms can benefit from a warmer urban
climate, which can help reduce heating demand and operational costs (Proksch
2017). Aquaponic farms that are integrated with the building systems of a host
building can further utilize urban resources such as waste heat and CO2 in exhaust air
to benefit the growth of plants as an alternative to conventional CO2 fertilization.
Urban farms can also help mitigate the negative aspects of the urban heat island
effect during the summer months. The additional vegetation, even if grown in
greenhouses, helps to reduce the ambient temperature through increased evapotrans-
piration (Pearson et al. 2010). In aquaponics, the use of recirculating water infra-
structure reduces overall water consumption for the production of both fish and
lettuce and can, therefore, have a positive effect on the urban water cycle.
Aquaponically-grown produce strives to close the nutrient cycle, thereby avoiding
the production of agricultural run-off. Through smart resource management within
major environmental systems, aquaponics helps to reduce excessive water consump-
tion and eutrophication usually created by industrial agriculture.
combine two complex growing systems (aquaculture and hydroponics), which both
require controlled growing conditions to guarantee optimal productivity. Addition-
ally, CEA enables year-round production to amortize high investment in aquaponic
infrastructure and achieve premium crop prices at the market outside of the natural
growing season. The performance of aquaponic farm enclosures is highly dependent
on local climate and seasonal swings (Graamans et al. 2018).
As aquaponics is a relatively young discipline, most of the existing research is
focused at the system level – for example, studies evaluating the technical integra-
tion of aquaculture with hydroponics in different configurations (Fang et al. 2017;
Lastiri et al. 2018; Monsees et al. 2017). Whilst individual aquaponic system
components and their interactions can still be further optimized for productivity,
their performance within a controlled environment envelope has not been compre-
hensively addressed. Recent research in CEA has begun to assess hydroponic system
performance in tandem with built environment performance, although there is only
one study to date that models aquaponic system performance in a controlled enve-
lope (Benis et al. 2017a; Körner et al. 2017; Molin and Martin 2018a; Sanjuan-
Delmás et al. 2018).
The current expansion in interest in aquaponics led to the creation of several interdis-
ciplinary aquaponics related research collaborations funded by the European Union
(EU). The COST FA1305 project, which created the EU Aquaponics Hub
(2014–2018) brought together aquaponics research and commercial producers to
better understand the state of the art in aquaponics and to generate coordinated
research and education efforts across the EU and around the world. Innovative
Aquaponics for Professional Application (INAPRO) (2014–2017), a consortium of
17 international partners, aimed to advance current approaches to rural and urban
aquaponics through the development of models and construction of prototypical
greenhouses. The project CITYFOOD (2018–2021) within the Sustainable Urban
Growth Initiative (SUGI), co-funded by the EU, Belmont Forum, and respective
science foundations, investigates the integration of aquaponics in the urban context
and its potential impact on global challenges of the food-water-energy nexus.
The term aquaponics is used to describe a wide range of different systems and
operations, greatly varying in size, technology level, enclosure type, main purpose,
and geographic context (Junge et al. 2017). The first version of the classification
criteria for aquaponic farms included stakeholder objectives, tank volume, and
parameters describing aquaculture and hydroponic system components (Maucieri
528 G. Proksch et al.
control, passive climate control strategies, and energy sources to achieve an appro-
priate indoor climate. The best application of each enclosure typology depends
primarily on the size of operation, geographic location, local climate, targeted fish
and crop species, required parameters of the systems it houses, and the budget. This
study identifies five different enclosure typologies and defines the characteristics of
indoor spaces that house aquaculture infrastructure.
The Aquaponic solar greenhouse (2000 sf/180 m2), developed and tested by
Franz Schreier, has proven as a suitable environment for housing a small aquaponic
system in southern Germany. The greenhouse collects solar energy through its
south-facing arched roof and wall clad with ethylene tetrafluoroethylene (ETFE)
film. Heat is stored in partially submerged fish tanks, floor, and adobe-clad northern
wall to be dissipated at night. The greenhouse’s custom-built photovoltaic
(PV) panels transform solar radiation into power. Located in the colder climate of
Vermont, USA, the Eco-Ark Greenhouse at the Finn & Roots farm (6000 sf/560 m2)
houses an aquaponic system that works with a similar passive solar approach. The
greenhouse has a steep (approx. 60 ) south-facing transparent roof with special solar-
collecting glazing (Fig. 21.5). Its highly insulated, opaque northern side is sub-
merged into a hillside and houses the fish tanks. In addition to these passive controls,
the Eco-Ark has a radiant floor heating that supplements heating during the coldest
seasons.
High-Tech Greenhouses Venlo-style, high-tech greenhouses that feature a high
level of technology to control the indoor climate are the standard for commercial-
scale hydroponic CEA. High-tech greenhouses are characterized by computerized
controls and automated infrastructure, such as automatic thermal curtains, automatic
lighting arrays, and forced-air ventilation systems. These technologies enable a high
level of environmental control, though they come at the cost of high energy
consumption.
534 G. Proksch et al.
Fig. 21.5 Eco-Ark Greenhouse at Finn & Roots Farm (Bakersfield, Vermont, USA)
Some large-scale commercial aquaponic farms use this greenhouse typology for
their plant production, such as Superior Fresh farms, located in Hixton, Wisconsin,
USA (123,000 sf/11,430 m2), with the aquaculture systems housed in a separate
opaque enclosure. Automated supplemental LED lighting and heating enables
Superior Fresh farms to cultivate leafy greens year-round despite lack of daylight
in the winter, where the natural, frost-free growing season lasts only 4 months.
Automated systems for internal climate control allow high-tech greenhouses to be
operated anywhere in the world – Blue Smart Farms greenhouse uses an array of
sensors to optimize shading during hot Australian summers.
Thanet Earth, the largest greenhouse complex in the UK, is located in the
southeast of England. Its five greenhouses cover more than 17 acres (7 hectares)
each, growing tomatoes, peppers, and cucumbers using hydroponics (Fig. 21.6).
This enterprise is powered by a combined heat and power system (CHP) that
provides power, heat, and CO2 for the greenhouses. The CHP system operates
very efficiently and channels excess energy to the local district by feeding it into
the local power supply grid. In addition, computer-controlled technologies such as
energy curtains, high-intensity discharge supplemental lighting, and ventilation
regulate the indoor growing conditions.
Rooftop Greenhouses This most recent type includes greenhouses built on top of
host buildings, either as retrofits of existing structures or as part of new construction.
Due to high land costs, saving space is increasingly important to aquaponic farms in
urban contexts. Connecting a greenhouse to an existing building is one strategy for
urban farmers looking to revitalize underused space and find a central location in the
city. Rooftop greenhouses are already used by commercial-scale hydroponic
growers but are a relatively rare enclosure type for aquaponic farms due to the
21 Aquaponics in the Built Environment 535
Fig. 21.6 Thanet Earth, state of the art greenhouses with combined heat and power provision, (Isle
of Thanet in Kent, England, UK)
additional weight of water which can strain existing structures beyond their loading
capacity. The few rooftop aquaponic farms that currently exist prioritize lightweight
water distribution systems (nutrient film technique or media-based growing rather
than deep water culture) and locate their fish tanks on the level below the crop
growing space due to relatively decreased demand for natural light.
Two rooftop farms with high-tech aquaponic systems have recently opened in
Europe. Both consulted with Efficient City Farming (ECF) farm systems consul-
tants in Berlin. Ecco-jäger Aquaponik Dachfarm in Bad Ragaz, Switzerland sits on
top of a distribution center of a family-owned produce company. The Venlo-style
rooftop greenhouse (12,900 sf/1200 m2) is located on a two-story depot building;
the fish tanks are installed on the floor below the greenhouse. By growing leafy
greens and herbs on their rooftop, Ecco-jäger reduces the need for transportation
and can offer produce immediately after harvest. In addition, the farm takes
advantage of waste heat generated by its cold storage to heat the greenhouse.
BIGH’s Ferme Abattoir (21,600 sf/2000 m2) is a larger version of a similar
Venlo-style rooftop greenhouse (Fig. 21.7), which occupies the roof of the Foodmet
market hall in Brussels, Belgium. These early examples point to further potential to
optimize both aquaponic and envelope performance through connecting water,
energy, and air flows between farm and host building, known as building-integrated
agriculture (BIA). Currently, research is being done on the flagship hydroponic
integrated rooftop greenhouse located on the building shared by the Institute
of Environmental Science and Technology (ICTA) and the Catalan Institute of
Paleontology (ICP) at the Autonomous University of Barcelona (UAB) to dermine
536 G. Proksch et al.
Fig. 21.7 BIGH Ferme Abattoir with the high-tech greenhouse in the background (Brussels,
Belgium)
the benefits of full building integration, although no such example exists in the field
of aquaponics to determine the benefits of full building integration, although no
such example exists in the field of aquaponics.
Indoor growing spaces rely exclusively on artificial light for plant production. Often,
these growing spaces are highly insulated and clad in an opaque material, originally
intended as storage or industrial manufacture rooms. Indoor growing spaces typi-
cally have better insulation than greenhouses due to the envelope material, though
cannot rely on daylighting or natural heating. The assumption is that this typology is
better suited to extreme climates, where temperature swings are of larger concern
than lighting (Graamans et al. 2018), though more conclusive research is needed.
Urban Organics operates two commercial-scale indoor growing aquaponic farms
within two refurbished breweries in the industrial core of St. Paul, Minnesota, USA.
The two farms cultivate leafy greens and herbs in stacked growing beds illuminated
by fluorescent grow lights (Fig. 21.8). Their second site allows Urban Organics to
tap into the brewery infrastructure around an existing aquifer; the aquifer water
needs minimal treatment and is supplied at 10 C to arctic char and rainbow trout
21 Aquaponics in the Built Environment 537
tanks. Using existing structures lowered construction costs for Urban Organics and
offered the opportunity to revitalize a struggling area of the city. In an even colder
climate, Nutraponics grows leafy greens in a warehouse on a rural parcel 40 km
outside Edmonton, Alberta, Canada. Since local produce is highly dependent on
seasonal temperature swings, Nutraponics gains a competitive edge in the market by
employing LED lighting to accelerate crop growth year-round (Fig. 21.9).
The enclosures for the aquaculture component of aquaponic operations are techni-
cally not as demanding as the enclosure design for the hydroponic components since
fish do not require sunlight to thrive. Nevertheless, control over indoor growing
conditions enables farmers to optimize growth, reduce stress, and draw up precise
schedules for fish production which gives their stock a competitive edge in the
market (Bregnballe 2015). Aquaculture space enclosures are mainly required to keep
water temperatures stable. Fish tanks should be able to support comfortable water
temperature ranges for specific fish species, warm-water fish 75–86 F (24–30 C)
and cold-water fish 54–74 F (12–23 C) (Alsanius et al. 2017). Water and room
temperature can be controlled most efficiently if fish tanks are housed in well-
538 G. Proksch et al.
insulated space with few windows to minimize solar gains during the summer
months and temperature losses when the outside temperature drops (Pattillo 2017)
as demonstrated in the set-up of the INAPRO enclosure. The large volume of water
required for fish cultivation needs to be considered from an architectural perspective,
as it carries consequences for structural and conditioning systems within a building.
greenhouse, which limits their selection of fish species to those with a large temper-
ature tolerance and draws their commercial focus to the production of lettuce, leafy
greens, and herbs.
Passive solar greenhouses rely on passive systems, specifically the use of thermal
mass, to control the indoor climate. The use of this typology for aquaponic systems is
advantageous since the large volume of water in the fish tanks provides additional
thermal mass. Due to their energy efficiency, they are often used in northern latitudes
where conventional greenhouses would require a high level of supplemental heating.
However, operating any greenhouse in those regions relies on the use of supple-
mental lighting due to low light levels and short daylight hours during the winter
season. Although passive solar greenhouses in Europe and North America are
currently used on a small experimental scale, the more general successful application
of these single-slope, energy-efficient greenhouses on 1.83 million acres (0.74
million hectares) of farmland in China shows that this typology can be successfully
implemented on a large scale (Gao et al. 2010).
High-tech greenhouses, especially large Venlo-style, gutter-connected systems,
are the industry standard for commercial hydroponic production. The largest well-
funded commercial aquaponic farms use this typology for their hydroponic growing
systems in conjunction with a separate enclosure for their aquaculture infrastructure.
This setup guarantees the highest level of environmental control as well as crop and
fish productivity. Technically, this type of greenhouse can be operated anywhere, as
long as the revenue produced pays for the high energy and operation costs in extreme
climates. However, this type of operation may not be environmentally sensitive in
some northern latitudes due to the extensive need for heating and supplemental
lighting. The exact environmental footprint of a high-tech greenhouse can only be
assessed on a per-project basis and depends mostly on the quality of energy sources
used for supplemental heat and light.
Most rooftop greenhouses are Venlo-style high-tech greenhouses constructed on
rooftops. Whilst similar benefits and challenges apply, the construction of rooftop
greenhouses is even more expensive than that of regular high-tech greenhouses,
primarily due to building codes and architectural requirements. The structural system
of rooftop greenhouses is often over-dimensioned to comply with building codes for
commercial office buildings, which are stricter than building code requirements for
agricultural structures. Furthermore, aquaponic operations on rooftops need addi-
tional infrastructure to access the roof and comply with fire and egress regulations,
which has generated a sprinkler equipped-greenhouse in a recent example (Proksch
2017). The most promising application of rooftop greenhouses is on top of host
buildings in urban centers. Urban roofs often offer ample access to sunlight, which
greenhouses require to function effectively – a resource that is usually lacking, or at
least is not consistent due to shadowing, at ground level in dense urban areas
(Ackerman 2012). If purposefully designed, host buildings can offer other resources
such as exhaust heat and CO2 that can make the operation of a rooftop aquaponic
farm more feasible. This type of integration with the host building can generate
energy and environmental synergies that improve the performance of both green-
house and host building.
540 G. Proksch et al.
Fig. 21.10 INAPRO aquaponics enclosure with two sections, opaque for fish and greenhouse for
plants (Murcia, Spain)
Indoor growing spaces depend entirely on artificial lighting and active control
systems for heating, cooling, and ventilation, which results in a high level of energy
consumption, environmental footprint, and operation cost. This typology is most
applicable in areas with cold winters and short growing seasons, where the natural
exposure to sunlight and heat gain is low and extensive supplementation is needed to
operate a commercial aquaponics greenhouse. The use of an opaque enclosure
allows high levels of insulation, which reduces heat loss during winter months and
provides autonomy from external temperature swings. Besides its dependence on
electrical lighting, indoor growing exceeds the productivity of greenhouses as
measured in other resources, such as water, CO2, and land area (Graamans et al.
2018). Additionally, the production per unit of land area can be much higher through
the use of stacked growing systems. Regarding the urban integration of aquaponics
in cities, indoor grow spaces allow for the adaptive reuse of industrial buildings and
warehouses, which can reduce the up-front cost for the construction of the enclosure
and support the integration of aquaponic farms in underserved neighborhoods.
The Innovative Aquaponics for Professional Applications (INAPRO, 2018) pro-
ject set-up included the comparison of the same state of the art aquaponic system and
greenhouse technology, across a number of sites in Germany, Belgium, and Spain.
The aquaponics system located in China was housed in a passive solar greenhouse.
The INAPRO aquaponics facilities in Europe utilized a glass-clad greenhouse type
for plant production and an industrial type shed component for fish tanks and
filtration units (Fig. 21.10). The INAPRO project demonstrates that greenhouse
21 Aquaponics in the Built Environment 541
technologies need to be adapted and chosen to suit local climate conditions. The
Spanish INAPRO team found, that the selected enclosure was well suited for the
cooler northern Europe regions, but not the warmer, Mediterranean regions in
southern Europe. This observation highlights the importance of more research on
the performance of greenhouses typologies to advance the field of commercial
aquaponics operations.
While the comparison of the different typologies reveals certain performance
patterns between typology, location, and investment (Table 21.3), for a comprehen-
sive understanding of farm performance and environmental impact, a more robust
system for the analysis and design of farm enclosures is needed.
The growth of aquaponics and generalized claims that aquaponics is more sustain-
able than other forms of food production has stimulated discussion and research into
how sustainable these systems actually are. Life cycle assessment (LCA) is one key
quantification method that can be used to analyze sustainability in both agriculture
and the built environments by evaluating environmental impacts of products
throughout their lifespan. For a building, an LCA can be divided into two types of
impact – embodied impact which includes material extraction, manufacture, con-
struction, demolition and disposal/reuse of said materials, and operational impact
which refers to building systems maintenance (Simonen 2014). Similarly,
conducting an assessment of an agricultural product can be also divided into the
structural impact of the building envelope and system infrastructure, production
impact associated with continuous cultivation and post-harvest impact of packaging,
storage, and distribution (Payen et al. 2015). Conducting an LCA of an aquaponic
farm requires the simultaneous understanding of both building and agricultural
impacts since there is an overlap in the envelope’s operational phase with a crop’s
production phase. The way a building operates its heating, cooling, and lighting
systems directly influences the cultivation of the crop; conversely, different types of
crops require different environmental conditions. Numerous studies exist comparing
LCA results for different building types situated in different contexts (Zabalza
Bribián et al. 2009). Similarly, LCA has been used by the agricultural sector to
compare efficiencies for different crops and cultivation systems (He et al. 2016;
Payen et al. 2015). Evaluating the performance of controlled environment agricul-
ture and aquaponics in particular requires a skillful integration of the two method-
ologies into one assessment (Sanyé-Mengual 2015).
The proposed aquaponic farm LCA framework (Fig. 21.11) is intentionally broad to
capture a wide range of farm typologies found in the field. In order to apply the results
of LCA to existing farms, factors such as climate and economic data must be included
to validate environmental assessment (Goldstein et al. 2016; Rothwell et al. 2016)
The following section discusses a collection of aquaponic farm enclosure design
strategies based on the LCA inventory of aquaponic farms that synthesizes existing
542 G. Proksch et al.
PROCESSES INPUTS
Infrastructure
Consumption
Fig. 21.11 Example of an integrated LCA process including building and aquaponic system
performance. (Based on Sanyé-Mengual et al. 2015).
544 G. Proksch et al.
literature with case studies and suggests directions for future work. The unique
integration of aquaponic and building-related impacts is of particular interest.
example, glass fiber-reinforced polyester used for the 100 m3 water tank at the ICTA-
ICP rooftop greenhouse is responsible for 10–25% of environmental impact at the
manufacturing stage (Fig. 21.13). The choice of substrate for plants in an aquaponic
system has a weight ramification for the structure of the host building, but also
contributes to environmental impact. In a recent study done on aquaponics integrated
with living walls, mineral wool, and coconut fiber performed comparably, despite one
being compostable and the other being single-use (Khandaker and Kotzen 2018).
Structure and Equipment Maintenance Initial material selection for aquaponic
equipment and envelope components determines the long-term upkeep of aquaponic
farms. Manufacturing more durable materials such as glass or rigid plastics requires
a greater initial investment of environmental resources than plastic films; however,
films require replacement more frequently – for example, glass is expected to remain
functional for 30+ years, whilst more conventional coated polyethylene film can
only last 3–5 years before becoming too opaque (Proksch 2017). Depending on the
intended lifespan of an aquaponic system envelope, it may be more advantageous to
choose a material with a shorter lifespan, and a lesser manufacturing impact. ETFE
film used in the Aquaponic solar greenhouse is a promising compromise between
longevity and sustainability, although further research is needed. Standard
aquaponic equipment consists of water tanks and piping. Piping for aquaponic
systems is often manufactured from PVC, which produces a significant environ-
mental impact in its manufacturing process but does not require replacement for up
to 75 years. Some aquaponic suppliers offer bamboo as an organic alternative.
546 G. Proksch et al.
Fig. 21.13 Building section with rooftop greenhouses by Harquitectes, ICTA-ICP building
(Bellaterra, Spain)
Energy In 2017, 39% of total energy consumption within the United States
corresponded to the building sector (EIA). The agricultural sector accounted for
approximately 1.74% of total U.S. primary energy consumption in 2014, relying
heavily on indirect expenditures in the form of fertilizers and pesticides (Hitaj and
Suttles 2016). Energy efficiency is a well-established field of research within both
the built environment and agriculture, often defining the operational impacts of a
product, building, or farm in the overall LCA (Mohareb et al. 2017). Integrating
building and agricultural energy use can optimize the performance of both (Sanjuan-
Delmás et al. 2018).
Heating Energy requirements for heating growing spaces are of particular interest
in the northern climates, where extending a naturally short growing season gives
building-integrated aquaponic farms a competitive edge in the market (Benis and
Ferrão 2018). However, in colder climates, energy consumption by active heating
systems is a significant contributor to overall environmental impact – in an
21 Aquaponics in the Built Environment 547
with the right ventilation strategy, fog cooling can be a water-saving technology
particularly suited to arid regions (Ishii et al. 2016). Additionally, fog cooling
decreases the rate of evapotranspiration in plants, which is critical to optimizing
plant metabolism in aquaponic systems (Goddek 2017). The flagship greenhouse of
Superior Fresh farms uses a computerized fog-cooling system to maintain cultivation
temperatures during the hot season.
Shading devices can also contribute to lowering greenhouse temperatures. Tra-
ditionally, the seasonal lime whitewashing of greenhouses was used to reduce solar
radiation levels during the hottest months (Controlled Environment Agriculture
1973). However, shading can be integrated with other building functions. A prom-
ising shading strategy is using semi-transparent photovoltaic modules to simulta-
neously cool the space and produce energy (Hassanien and Ming 2017). The
Aquaponic solar greenhouse combines its photovoltaic array with shading function-
ality; it uses rotating aluminium panels as shading devices that operate as solar
collectors with the help of mounted photovoltaic cells. The integrated photovoltaic
system then transforms excess solar radiation into electrical energy.
Lighting The main advantage of greenhouses over indoor growing spaces is their
ability to capitalize on daylight to facilitate photosynthesis. However, farms in
extreme climates may find that satisfying heating or cooling loads for a transparent
envelope is not financially feasible; in this case, farmers may choose to cultivate crop
in indoor growing spaces with an insulated envelope (Graamans et al. 2018).
Aquaponic farms that operate in indoor growing spaces rely on efficient electrical
lighting to produce crops.
Many advances in contemporary farm lighting originated in Japanese plant
factories, used to optimize plant yields in dense hydroponic systems by replacing
sunlight with engineered light wavelengths (Kozai et al. 2015). Currently, LED
lighting is the most popular choice for electrical horticultural lighting systems. They
are 80% more efficient than high-intensity discharge lamps and 30% more efficient
than their fluorescent counterparts (Proksch 2017). LED lighting continues to be
investigated to optimize energy efficiency and crop yield (Zhang et al. 2017). Large-
scale greenhouses like Superior Fresh, Wisconsin, USA rely on computerized,
supplemental lighting regimes to extend the photosynthesis period of its crop in
northern latitudes.
Energy Generation Constrained by the same factors as all CEA, the energy
management of an aquaponic farm depends on exterior climate, crop selection, the
production system, and structure design (Graamans et al. 2018). Growing produce
through aquaponics is not inherently sustainable if not managed properly – all of the
factors above can affect energy efficiency for the better or worse (Buehler and Junge
2016). In many cases, CEA is more energy-intensive than conventional open-field
agriculture; however, higher energy expenditures may be justified if the way we
source energy shifts toward renewable sources and efficient strategies for heating,
cooling, and lighting are incorporated into the design of the farm.
Photovoltaic (PV) power generation can play an important part in offsetting
operational impacts for controlled environment aquaponics, reducing environmental
21 Aquaponics in the Built Environment 549
The integration of different fish and crop nutrient needs is a challenge in single-
recirculating aquaponic systems (Alsanius et al. 2017). Generally, plants require
higher nitrogen concentrations than fish can withstand and careful crop and fish
selection can match nutrient requirements to optimize yields, but is still difficult to
achieve. Decoupled systems (DRAPS) have been proposed to separate the aquacul-
ture water cycle from the hydroponic one to achieve desired nutrient concentrations,
but is not yet commonly applied in commercial farms (Suhl et al. 2016). Urban
Organics based in St. Paul, Minnesota, USA chose to develop a DRAPS system for
their second farm to optimize both crop and fish yields and avoid crop loss in case of
nutrient imbalances within fish tanks. ECF Farm in Berlin, Germany, and Superior
Fresh farms in Wisconsin, USA also operate decoupled systems to optimize fish and
plant growth.
Alternatively, aquaponic nutrient cycles can be optimized through the introduc-
tion of an anaerobic reactor to transform solid fish waste into plant-digestible
phosphorus (Goddek et al. 2016). Currently, The Plant in Chicago, USA is planning
to operate an anaerobic digester which may play a part in optimizing nutrient cycles
for crop growth. The mechanical system requirements for DRAPS and anaerobic
digestion will influence the performance as well as the spatial layout of an
aquaponic farm.
matched (Stadler et al. 2017). While aquaponics requires a relatively costly initial
investment, it may outperform conventional farming during the production and
distribution phase where the design of the recirculating water system reduces
water costs, and greatly reduces the need for fertilizers, which usually comprise
between 5% and 10% of overall farm costs (Hochmuth and Hanlon 2010). However,
estimating the economic viability of aquaponic farms is particularly challenging due
to the range of dynamic factors affecting performance including the local price for
labor and energy being two examples (Goddek et al. 2015). In an economic analysis
of aquaponic farms in the Midwestern United States, labor constituted 49% of all
operational costs despite the assumption that only minimum wages would be paid. In
reality, the wide range of expertise required to operate an aquaponic system will
likely warrant higher wages in an urban farm scenario (Quagrainie et al. 2018).
Site selection and envelope design have a direct relationship to the profitability of
an aquaponic farm by affecting operation efficiency and how broad the potential
market can be. Aquaponic farms located in urban environments can tap into multiple
markets outside agricultural production, where many aquaponic farms offer tours,
workshops, design consulting services, and supply backyard aquaponic systems for
hobbyists. Integrating agriculture with other types of spaces within urban environ-
ments can contribute to the financial health of aquaponic farms. The ECF aquaponic
farm is located on the work yard of the industrial landmark building Malzfabrik,
Berlin, Germany, which operates a cultural center and houses work spaces for artists
and designers.
Urban agriculture is often cited as a strategy to provide fresh food for underserved
communities located in food deserts, yet few commercial urban farms target this
demographic, proving that commercial-scale urban agriculture can be just as exclu-
sionary as conventional supply chains (Gould and Caplow 2012; Sanyé-Mengual
et al. 2018; Thomaier et al. 2015). Aquaponic farms that use high-tech infrastructure
try to redeem their high investments by achieving premium prices in urban markets,
though aquaponics can also stem from grassroots and hobbyist applications.
Aquaponics may also have the potential to increase food security for urban residents.
This is evidenced in the lasting legacy of Growing Power, a non-profit organization
that until recently, ran an urban farm in Milwaukee, Wisconsin, USA started by Will
Allen in 1993. Many current aquaponic farmers attended Growing Power’s work-
shops, in which Allen championed an aquaponic model that gives back to the
surrounding community by means of community-supported agriculture boxes and
classes. Initiated by Growing Power’s educational programs, other aquaponic
non-profit organizations have taken up to the torch such as Dre Taylor with Nile
Valley Aquaponics in Kansas City, Kansas, USA. This farm aims to provide
100,000 pounds (45,400 kg) of local produce to the surrounding community in an
award-winning new campus for the expanding farm (Fig. 21.14).
21 Aquaponics in the Built Environment 553
Fig. 21.14 Proposed Nile Valley Aquaponics campus (Kansas City, Kansas, USA) by HOK
Architects
21.7 Conclusions
There is an array of criteria that contribute to the performance of each farm and their
number grows with the number of disciplines involved in this the interdisciplinary
field of aquaponics. Of note is an earlier study that has provided a definition of
aquaponics and a classification of the types of aquaponics based on size and system
554 G. Proksch et al.
(Palm et al. 2018). Many criteria for the analysis of the enclosure type identified in
this study stem from immediate farm context – local climate, the quality of the built
environment context, energy sourcing practices, costs, market, and local regulatory
frameworks. An aquaponic greenhouse in a rural context performs differently than
one in a city, just as farms in arid climates do not share the same requirements as their
counterparts in colder areas. In general, greenhouses classified as medium-tech and
passive solar offer a lower cost, environmentally sustainable enclosure option,
currently only used by smaller aquaponic operations. However, due to their inten-
tionally limited level of technical environmental controls, they only perform well in
specific climate zones. In comparison, high-tech and rooftop greenhouses can be
technically implemented anywhere, though in extreme climate conditions they
generate high operational costs and larger environmental footprints. Recent case
studies show that indoor growing facilities can be financially feasible, but due to
their exclusive reliance on electrical lighting, their resource use efficiency and
environmental footprint are of concern. Further research is needed to establish the
relationship of specific aquaponic farms and their enclosures to existing resource
networks. This work can help connect aquaponics to research done on urban
metabolism.
Other criteria determining farm typology and performance are internal. These
include environmental control levels, crop and fish selection, aquaponic system type
and scale and enclosure type and scale. Taking on an integrated LCA approach, the
relationship between all factors have to be assessed throughout the lifespan of the
farm, from cradle to grave. Life cycle assessment of aquaponic farms must include
both building impacts and growing system impacts since there is overlap in the farm
operation phase. A series of promising strategies in heating, cooling, lighting, and
material design can improve overall farm efficiency throughout the entire lifespan of
the farm. Beyond accounting for environmental impact, LCA can become a design
framework for horticulture experts, aquaculture specialists, architects, and investors.
Continuing to survey existing commercial aquaponic farms is important to
validate LCA models, identify strategies, and cataloguing aquaponic operations
emerging on a larger scale. Combining modeling with case study research on
controlled environment aquaponics has the potential to connect aquaponics to the
larger scope of urban sustainability.
Acknowledgments The authors of this study acknowledge the financial support of the National
Science Foundation (NSF) under the umbrella of the Sustainable Urbanization Global Initiative
(SUGI) Food Water Energy Nexus and the support of all CITYFOOD project partners for providing
ideas and inspiration.
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21 Aquaponics in the Built Environment 557
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Part V
Aquaponics and Education
Chapter 22
Aquaponics as an Educational Tool
R. Junge (*)
Institute of Natural Resource Sciences Grüenta, Zurich University of Applied Sciences,
Wädenswil, Switzerland
e-mail: ranka.junge@zhaw.ch
T. G. Bulc
Faculty of Health Sciences, University of Ljubljana, Ljubljana, Slovenia
e-mail: tjasa.bulc@zf.uni-lj.si
D. Anseeuw
Inagro, Roeselare, Belgium
e-mail: info@inagro.be
H. Yavuzcan Yildiz
Department of Fisheries and Aquaculture, Ankara University, Ankara, Turkey
e-mail: yavuzcan@ankara.edu.tr
S. Milliken
School of Design, University of Greenwich, London, UK
e-mail: S.Milliken@greenwich.ac.uk
22.1 Introduction
2015), respondents indicated that aquaponics were often used to teach subjects,
which are more exclusively focused on STEM topics. Aquaponics education in
primary and secondary schools is science-focused, project-oriented, and geared
primarily toward older students, while college and university aquaponics were
generally larger and less integrated into the curriculum. Interdisciplinary subjects
such as food systems and environmental science were taught using an aquaponics
more frequently at colleges and universities than they were at schools, where the
focus was more often on single discipline subjects such as chemistry or biology.
Interestingly, only a few vocational and technical schools used aquaponics to teach
subjects other than aquaponics. This indicates that for these educators, aquaponics is
a stand-alone subject and not a vehicle to address STEM or food system topics
(Genello et al. 2015).
While the studies mentioned above reported aquaponics as having the potential to
encourage the use of experimentation and hands-on learning, they did not evaluate
the impact of aquaponics on learning outcomes. Junge et al. (2014) evaluated
aquaponics as a tool to promote systems thinking in the classroom. The authors
reported that 13–14 year old students (seventh grade in Switzerland) displayed a
statistically significant increase from pre- to post-test for all the indices measured to
assess their systems thinking capacities. However, since the pupils did not have any
prior knowledge of systems thinking, and since there was no control group, the
authors concluded that supplementary tests are needed to evaluate whether
aquaponics has additional benefits compared to other teaching tools. This issue
was addressed in the study by Schneller et al. (2015) who found significant advances
in environmental knowledge scores in 10–11 year old students compared to a control
group of 17 year olds. Moreover, when asked for their teaching preferences, the
majority of students indicated that they preferred hands-on experiential pedagogy
such as aquaponics or hydroponics. The majority of the students also discussed the
curriculum with their families, explaining how hydroponic and aquaponics work.
This observation extends the belief that hands-on learning using aquaponics (and
hydroponics) not only has a stimulating impact on teachers and students, but also
leads to intergenerational learning.
The objective of this chapter is to provide an overview of possible strategies for
implementing aquaponics in curricula at different levels of education, illustrated by
case studies from different countries. Based on evaluations conducted with some of
these case studies, we attempt to answer the question of whether aquaponics fulfils
its promise as an educational tool.
Small Scale
Aquaponic
Societal Farmers
Vocational Added Value:
Research & Tertiary
Education and Schools, Consumers
Development Education
Training Health, Business,
Community (Commercial
Farms,
Suppliers,
Retailers)
Fig. 22.1 An aquaponics can address various goals or stakeholders by offering to develop key
competences in appropriate educational and training processes. (Modified after Graber et al. 2014)
There are, as stated above, many aquaponics described and illustrated on the web. It
is also possible to purchase a kit, or have a complete system delivered and installed.
However, building an aquaponics is in itself a valuable educational experience, and
the fact that it is not delivered to the classroom ready-made adds to its instructional
value.
An aquaponics can address various goals or stakeholders (Fig. 22.1). To attain all
of these, the components of a system have to fulfill various requirements
(Table 22.1). The choice of what kind of aquaponics is suitable for a particular
institution should result from a realistic assessment of its facilities and the educa-
tional objectives.
Maucieri et al. (2018) proposed a general classification of aquaponics according
to different design principles. While a system can simultaneously fulfill several
objectives, including greening and decoration, social interaction, and food produc-
tion, here we assume that the main objective is education. If we follow the classi-
fication of Maucieri et al. (2018), which categorizes the aquaponics according to
several categories (stakeholder, size), several distinct options for choosing a suitable
aquaponics emerge (Table 22.2). Any decision has to be made within the limits of
the available budget, though it is possible to construct a system at very low cost.
22 Aquaponics as an Educational Tool 565
Table 22.2 Suitability of different design options for an educational aquaponics. The green color
denotes the most suitable options, yellow options are less suitable, while red options are not suitable
for the majority of cases
a
Extensive (fish density is mostly under 10 kg/m3 and allows for integrated sludge usage in
grow beds).
b
Intensive (fish density requires additional sludge separation; however, the sludge has to be treated
separately).
c
Closed loop (“coupled” systems): after the hydroponic component, the water is recycled to the
aquaculture component.
d
Open loop or end-of pipe (“decoupled” systems): after the hydroponic component, the water is
either not or only partially recycled to the aquaculture component.
aquarium from an aquarist among the staff or the students, who would also be
able to give advice on fish care.
– Are the fish going to be harvested? Animal welfare should always be observed
and killing the fish should be done according to animal protection laws (Council
of the European Union 1998). Children might have problems in killing and eating
a living animal, which resembles Dory (from the movie finding Nemo). If the fish
are not going to be harvested, then goldfish or Koi are a good option.
– Are the plants going to be harvested and eaten? If yes, then suggestions for using the
produce need to be prepared. If not, then consider using ornamental plants instead.
An aquaponics with living fish and plants obviously provides the potential for long-
term engagement compared to conventional single discipline scientific experiments.
While this is a manifest asset for progressive and continuous experiential learning, it
has been indicated that safeguarding the teacher’s interest in the long run and the
provision of learning material are key challenges to successfully incorporating
aquaponics in school classes (Hart et al. 2013; Clayborn et al. 2017).
22 Aquaponics as an Educational Tool 567
Fig. 22.2 (a) Opening ceremony in the school of Älandsbro, (b) The simple aquaponics at
Älandsbro, (c) Older students making observations for the “Recirculation Book,” (d) Model built
by the younger students during an arts class
way of providing sustained and continuous engagement can be through the building,
management, and maintenance of an aquaponics.
Key advice for introducing aquaponics to primary school students is as follows:
• Low-tech and robust classroom systems favor the engagement of both the
teacher and the students and are most effective for this stage of education
(Example 22.1, Fig. 22.2b).
• Productivity is not a central issue but demonstrating the laws of nature (cycling of
nutrients, energy flow, population dynamics, and interactions within the ecosys-
tem) is. Therefore, sufficient effort needs to be put into developing learning
materials to meet the goals of the curriculum.
• From an educational point of view, understanding the chemical, physical, and
natural processes in an aquaponics, albeit through trial and error, is more impor-
tant than achieving a perfectly run system.
22 Aquaponics as an Educational Tool 569
• Include a wide range of activities: drawing the plants and animals, keeping a class
journal, measuring the water quality, monitoring the fish (size, weight, and well-
being), feeding the fish, cooking the produce, role playing, writing, prose, poetry,
and song.
Fig. 22.3 (a) Students from the sixth grade of Gerberacher School visiting the demonstration
aquaponics at Zurich University of Applied Sciences (Waedenswil, Switzerland). (b) A poster
designed by the same students, explaining the basics of aquaponics
(continued)
572 R. Junge et al.
(continued)
22 Aquaponics as an Educational Tool 573
Outflow
Pump
Aquarium
30 cm x 60 cm x 40 cm
Volume 80 l
Fig. 22.4 Simple classroom aquaponics. (Adapted after Bamert and Albin 2005). The plants grow
in the containers filled with light expanded clay aggregate (LECA) that is usually used in
hydrocultures
574 R. Junge et al.
Table 22.3 Sequence of teaching units in three classes of seventh grade students during one
semester course in a Grammar School in Switzerland
Number
Teaching of
unit lessons Methods Content
TU1 1 Survey of existing Pre-activity Test
knowledge
TU2 4 Lecture by teacher, System basics
research, & presentations
by students
TU3 2 Lecture by teacher, stu- “Connection circle” tool allows the students
dent assignment to draw a diagram of a system (adopted
from Quaden and Ticotsky 2004)
TU4 2 Discovery learning Planning an aquaponics: sub-units,
Presentations by students connections
TU5 2 Problem-based learning Defining the main indicators of the system:
(PBL) Fish and plants and their interactions
TU6 3 Discovery learning Monitoring the aquaponics
TU7 3 Presentations by students Drawing a diagram of the interconnections
in the aquaponics
TU8 1 Survey of knowledge Post-activity test
TU9 2 Aquaponic party Harvest, preparation of salad, eating
Modified after Junge et al. (2014)
The European Union invested in the development of vocational education via the
Leonardo Program, and more recently ERASMUS+. These programs have funded
several projects that included the implementation of aquaponics, including the
Leonardo da Vinci Transfer of Innovation Project (Lifelong Learning Programme)
“Introducing Aquaponics in VET: Tools, Teaching Units and Teacher Training”
(AQUA-VET)’. The project prepared a curriculum for vocational education in
aquaponics and the results are available at www.zhaw.ch/iunr/aquavet. The teaching
units were tested at three vocational schools in Italy, Switzerland (Baumann 2014),
and Slovenia (Peroci 2016). As part of this project an aquaponics unit was constructed
at the Biotechnical Centre Naklo vocational school in Slovenia (Example 22.5).
Another example is the aquaponic unit built at the Provinciaal Technisch Insituut, a
horticulture school in Belgium (Example 22.6).
Fig. 22.5 (a) Aquaponics at the Biotechnical Centre Naklo in Slovenia. (Photo: Jarni 2014). (b)
Practical work at the aquaponic unit of the Biotechnical Centre Naklo. (Photo Peroci 2016)
22 Aquaponics as an Educational Tool 577
Higher education programs need to be adapted to meet the expectations of the new
millennium, such as long-term food security and sovereignty, sustainable agricul-
ture/food production, rural development, zero hunger, and urban agriculture. These
important drivers mean that higher education institutions involved in the areas of
food production can play a key role in the teaching of aquaponics through both
capacity development and knowledge creation and sharing. Additionally, it is clear
that the interest in teaching and learning aquaponics is increasing (Junge et al. 2017).
At universities and colleges, aquaponics is usually taught as part of agriculture,
horticulture, or aquaculture courses and the context for course content development
in higher education is specific to each institution’s internal and external dynamics.
The main challenge in designing courses at higher education level is the interdisci-
plinary nature of aquaponics, as prior knowledge of both aquaculture and horticul-
ture is essential. While some studies investigated the use of aquaponics in education
(Hart et al. 2013; Hart et al. 2014; Junge et al. 2014; Genello et al. 2015) and a
number of on-line courses are available, a course outline for aquaponics at the
tertiary level at a main-stream does not yet exist, or at least hasn’t been published.
For tertiary level aquaponics courses to be implemented in the EU, the Bologna
Process, which underlines the need for meaningful implementation of learning
outcomes in order to consolidate the European Higher Education Area (EHEA),
578 R. Junge et al.
needs to be followed. Learning outcomes are (i) statements that specify what a
learner will know or be able to do as a result of a learning activity; (ii) statements of
what a learner is expected to know, understand, and/or be able to demonstrate after
completing a process of learning; and (iii) are usually expressed as knowledge,
skills, or attitudes (Kennedy 2008).
Table 22.4 and Example 22.7 introduce two conceptual frameworks for teaching
aquaponics. Both courses are considered to be worth 5 ECTS credits (European
Credit Transfer System), which correspond to a study load of approximately 150 h.
(continued)
22 Aquaponics as an Educational Tool 579
Table 22.4 Proposed aquaponics course outline at university level (5 ECTS). The flexible frame-
work contains two key topics (hydroponics and aquaculture) and is clustered into six learning areas
Course title: Aquaponics
Course Aquaponics is a food production method that combines hydroponics and
Description: aquaculture to form a system that re-circulates the water and nutrients and
grows terrestrial and aquatic plants including algae and aquatic organisms
while minimizing waste discharge. This course allows students to use the
technical skills acquired to set up an integrated system. It equips them with
the knowledge needed to be able to undertake and be aware of critical
aspects of aquaponics.
Entry Level: BSc or MSc
Unit Name 1. Aquaponics 2. Aquaponics Operations
Unit Purpose To understand system design and man- To understand water characteris-
agement, components, and construction tics, the microbiological and
techniques. biochemical cycles (e.g., the
nitrogen cycle) within an
aquaponics, and interactions
between water and plants.
Recommended Basic knowledge of biology and agri- Basic knowledge of water qual-
prior knowledge culture (horticulture and aquaculture). ity, aquatic organisms, aquatic
and skills: microbiology.
Learning Students should be able to Students should be able to
outcomes explain the characteristics of an explain water quality
aquaponics; parameters;
explain the types of aquaponics; explain biochemical cycles
and microbial transformations;
explain the construction techniques; identify criteria for fish and
and plant production;
describe the operational calculate all relevant fish
components. growth parameters; and
explain harvesting and
processing.
(continued)
580 R. Junge et al.
Table 22.5 Summarized answers of the six interviewed teachers regarding the advantages and
disadvantages of using aquaponics as a teaching tool
Number of What are the main Number of
What are the main advantages? mentions disadvantages? mentions
Suitable to learn system thinking 3 None. 2
Facilitates teamwork 2 High time requirements. 2
mobilization of students 2 High knowledge 2
requirements.
Provides diversity in teaching 2 Difficult concepts & 1
language.
Motivating for students 1 Sensitive for pests. 1
Motivating for teachers 1 Students were not always 1
paying attention.
Transfer between different sub- 1
jects possible
Versatile: several possible edu- 1
cational objectives
22 Aquaponics as an Educational Tool 583
Peroci (2016) investigated a series of aspects related to the potential for including
aquaponics in the educational process of secondary vocational education in Slovenia
(Fig. 22.7). This included
Interview of
Analysis of
Student Educators
Knowledge
Survey Using
Catalogs
Aquaponics
Views on Food
Course Preparation Knowledge of Preparation
Produced in
Design of Lessons Aquaponics of Lessons
Aquaponics
Pretest of
Existing
Knowledge
Course
Implemen-
tation
Posttest of
Testing Skills Evaluation
Knowledge
Fig. 22.7 The general structure of the study of Peroci (2016) about the potential for including
aquaponics in the educational process of secondary vocational education in Slovenia
584 R. Junge et al.
The aim of the Waste Water Resource project was to assemble, develop, and assess
teaching and demonstration material on ecotechnological research and methods for
pupils aged between 10 and 13 years (http://www.scientix.eu/web/guest/projects/
project-detail?articleId¼95738). The teaching units were assessed in order to
improve the methods and content and maximize learning outcomes. Based on
discussions with educational professionals, the assessment was based on a simple
approach using questionnaires and semi-structured interviews. Teachers assessed the
units by answering the online questionnaire (see Sect. 22.7.1). The aquaponic units
were evaluated in Sweden (in the Technichus Science Center, and in Älandsbro
skola in Härnösand), and in Switzerland.
Between 2006 and 2008, an aquaponic unit was installed at Technichus, a science
center in Härnösand, Sweden (www.technichus.se). The questionnaire was placed
beside the system so that the visiting students could answer the questions at any time.
It consisted of 8 questions (Fig. 22.8).
The answers showed that the students understood how the water in the system
was re-circulated. They understood less well how nutrients were transported within
the system and the contents of the nutrients and, interestingly, one in four students
did not know that the plants growing in the aquaponic unit were edible.
The questionnaire used in Älandsbro skola was first explained by the teacher in order
to ensure that the students would understand the questions. The questions were
answered before the project started and at the end of the project.
Fig. 22.8 Questionnaire and the frequency of answers of the 24 students (aged from 8 to 17 years)
visiting the exhibition in Technichus, Sweden
586 R. Junge et al.
On average, there were 28% more correct answers to the general questions about
nutrient requirements of plants and fishes after the teaching unit. As expected, and
similar to the findings of Bamert and Albin (2005), the increase in knowledge was
evident.
The conclusions of the investigation were that (i) working with aquaponics has a
great potential to help pupils attain relevant learning goals in the Swedish curriculum
for biology and natural sciences; (ii) the teachers thought that the work gave natural
opportunities to talk about cycling of matter and that it attracted the pupils’ interest;
(iii) the questionnaires showed that a large number of pupils had changed their
opinion about the needs of fish and plants before and after they worked with the
system; and (iv) the interviews with the older pupils showed that they had acquired
good knowledge about the system.
Even more important, all the people involved (teachers and students) found that
aquaponics provided the means to expand the horizon of the discipline, in a
refreshing and effective way.
The effect of the teaching sequence described in Example 22.3 on systems thinking
competencies was assessed at the beginning and at the end of the sequence. The
22 Aquaponics as an Educational Tool 587
Fig. 22.9 Answers of students from two different environments (Donat-rural and Waedenswil-
urban) about what they liked/disliked most in the aquaponic lessons
Table 22.7 Comparison of the median delineation scores between the pre- and post-test
Pre-activity test (median) Post-activity test (median) Change
Girls 2.5 7 4.5
Boys 2 7 5
pattern emerged (Table 22.7). While both genders reached the median level of
7, meaning that the majority of drawings contained at least one loop and/or cycle,
at the end of the teaching sequence, the change was more marked among the boys,
who started at a lower level. This indicated that boys profited more from hands-on
experience than girls.
In the next step, the Complexity index, Interconnection index, and the Structure
index were calculated (for details, see Junge et al. 2014).
The complexity index (German: Komplexitätsindex, KI) shows how many sys-
tem concepts the student implemented:
VI ¼ 2 x arrows=variables ð22:2Þ
The structure index (Strukturindex, SI) shows how many complex system con-
cepts the student implemented in the representation:
The students found more system concepts and knew more about system variables
at the post-test than in the pre-test, a fact reflected by all indices applied (Fig. 22.10).
These results appear to support the hypothesis that incorporating aquaponics into
teaching has a positive influence on the systems thinking capabilities of students, and
that the devised “Classroom Aquaponic Sequence” was successful in training
students in systems thinking.
22 Aquaponics as an Educational Tool 589
20
15
10
5
Female
0 Male
Pretest Posttest
1,6
Interconnection Index (VI)
1,2
0,8
0,4
Female
0 Male
Pretest Posttest
0,5
Structure Index (SI)
0,4
0,3
0,2
0,1
Female
0 Male
Pretest Posttest
Fig. 22.10 Complexity of answers in pre-activity and post-activity tests. Above: Complexity Index
(KI), centre: Interconnection Index (VI), below: Structure Index (SI)
590 R. Junge et al.
The learning progression of the short aquaponic course within the study of Peroci
(2016) (see Precedent 5) was assessed by means of questionnaires: (i) pre-test/post-
test; (ii) test of the acquired skill level in connection with food production in
aquaponics; and (iii) teaching evaluation.
The influence of various factors on the popularity of the lessons and the practical
work was evaluated. Students named several factors as being crucial for their interest
in the aquaponics course. The most relevant factors were: more relaxed teachers
(80%); entertainment (76%); attractive location of the practical work (72%); contact
with nature (68%); active practical work (64%); and use of interesting new methods
(56%). Generally, students rated the more interesting lessons as those that were less
difficult (e.g., the lesson “Monitoring water quality and bacteria” was less interesting
and most difficult) (Fig. 22.11).
Peroci (2016) investigated knowledge, attitudes toward food produced, and interest
in the use of aquaponics among students at 8 secondary vocational schools in
biotechnical fields within the educational programs for land manager (1st–third
year), horticultural technician (1st–fourth year), technician in agriculture and man-
agement (1st–fourth year), and environmental technician (1st–fourth year) during
2015 and 2016.
The survey involved a 15-minute questionnaire, with closed-ended answers (yes
or no). The survey showed that 42.9% of 1049 students had already heard about
aquaponics. They had learnt about it at school (379 students), from the media (79),
from peers and acquaintances (42), from advertisements (18), when visiting the
aquaponics (12), at agricultural fairs (2), and in aquaristic (1). Most of the positive
answers were from students from the Biotechnical Center Naklo where the
aquaponics was constructed in 2012 (Podgrajšek et al. 2014) and aquaponics was
already integrated in the learning process; 28% of respondents lacked any knowl-
edge about aquaponics and 19.8% of respondents said they would choose the
aquaponics course over other modules, mostly because of its interdisciplinary nature
and due to its sustainable and creative approach. The students also expected that after
attending such a course, they would have better chances of finding a job. Most
students liked the practical work, and 10.7% of respondents said they would like to
volunteer by maintaining the aquaponics and that they would like to set up their own
aquaponics. The analysis regarding the interest of students in producing food using
aquaponics showed that they liked this idea. However, they were not sure if they
22 Aquaponics as an Educational Tool 591
Perceived Interest
Tutorials
Plants
Fish
Monitoring Water
Quality and Bacteria
Aquaponics
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
1-low 2 3 4 5-high
Perceived Difficulty
Tutorials
Plants
Fish
Monitoring Water
Quality and Bacteria
Aquaponics
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
1-low 2 3 4 5-high
Fig. 22.11 Evaluation of the perceived interest (above) and difficulty (below) of aquaponics
lessons at the vocational school in Naklo, Slovenia. (Modified after Peroci 2016)
would eat the fish and vegetables produced in this way, mostly because they had no
previous experience of eating food produced in an aquaponics. Based on these
results, we can assume that the production of food in aquaponics will be well
accepted by the students of secondary vocational schools in biotechnical fields.
This is important as these students are the next generation of entrepreneurs, farmers,
and technicians who will not only generate, make, and evolve aquaponics in the
future but also help generate the confidence in aquaponics among stakeholders so
that it becomes part of food production in Slovenia in the future.
592 R. Junge et al.
A key issue for the successful dissemination of new teaching units appears to be a
robust integration of the units into the national school frameworks. The feedback
from the schools strongly indicates that teachers have very limited time to find and
initiate new ideas and teaching materials. They usually use already established
information portals that provide the material in a form that corresponds to the
national education plan and is ready-made for a particular school level. There is
therefore a need to establish cooperation with the key players in the national
pedagogical frameworks. In order to better evaluate the impacts of aquaponics on
STEM subjects, environmental and other learning outcomes, a comparative study
between educational institutions where they used aquaponics as a teaching tool
based on the same and well-designed research methods and addressing various
teaching goals would be needed.
Acknowledgments This work was partly supported by funding received from the COST Action
FA1305 “The EU Aquaponics Hub—Realising Sustainable Integrated Fish and Vegetable Produc-
tion for the EU.”
We acknowledge the contribution of the EU (FP6-2004-Science-and-society-11, Contract
Number 021028) to the project “WasterWater Resource,” and thank the entire team, especially
Nils Ekelund, Snorre Nordal, and Daniel Todt.
We acknowledge the contribution of the EU (Leonardo da Vinci transfer of innovation project,
Agreement Number - 2012-1-CH1-LEO05-00392) to the project Aqua-Vet, and thank the entire
team, especially Nadine Antenen, Urška Kleč, Aleksandra Krivograd Klemenčič, Petra Peroci, and
Uroš Strniša.
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22 Aquaponics as an Educational Tool 595
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Chapter 23
Food, Sustainability, and Science Literacy
in One Package? Opportunities
and Challenges in Using Aquaponics
Among Young People at School, a Danish
Perspective
Abstract The call for sustainable food production and consumption has led to an
increased interest and new policy measures to support the circular economy and
climate-smart farming practices. The merits of aquaponics and closed-loop nutrient
cycling systems are increasingly being examined in terms of sustainable productivity
in various settings including urban environments. Aquaponics also has the potential
to be applied as a learning tool for people of all ages but especially for young people
at school. This chapter studies the potential of aquaponics to teach food and science
literacy and the use of the technology as an educational tool in primary school. The
chapter draws on data from the Growing Blue & Green (GBG) program carried out
in cooperation among Aalborg University, Copenhagen, municipal schools and their
teachers and a private aquaponic enterprise. The chapter draws on three empirical
studies including an exploratory study on the educational opportunities at school, a
feasibility study carried out among teachers, as well as the educational Growing Blue
& Green (eGBG) study, in which a digital-based regulation component was added.
The conclusion is that low-cost versions of aquaponics have considerable potential
for supportive learning in elementary school. Preliminary findings furthermore
suggest that fitting the setup with easy-to-install intelligent sensors and devices
offers the opportunity to provide learning about food, sustainability, and a basic
understanding of the control and management of biological systems in one package.
B. E. Mikkelsen (*)
Integrated Food Studies, Aalborg University Copenhagen, Copenhagen, Denmark
e-mail: bemi@learning.aau.dk
C. M. Bosire
Department of Learning & Philosophy, Aalborg University, Copenhagen, Denmark
23.1 Introduction
Fig. 23.1 The aquaponic learning and experimental mock-up. The illustration shows the setup
including aquarium fish tank and the monitoring devices that are used to measure the equilibrium of
the whole system. The last part is the core of the learning goal for students. (Pictures: courtesy of
Lija Gunnarsdottir)
and the promotion of lifelong learning opportunities for all (UN 2015b). These
crucial issues can be included in the Problem-Based Learning (PBL) approach that
has been developed in the GBG case. Based on a shared firm belief in having
technological solutions for the problems of contemporary food systems, the GBG
approach contributes to a demonstration of “ecological modernization” in food
production processes. Through the development of the didactic for the eGBG themes
of sustainability and food literacy, it became clear that for such a system to bring
about change, there is a need for the right platform through which knowledge and
skills can be exchanged among young people and their teachers in the school setting.
Other studies have shown that the lack of food and nutrition literacy among
young people is of growing concern (Vidgen and Gallagos 2014; Dyg and
Mikkelsen 2016). This is particularly concerning, as the conventional ways of
food production and the current persistent drivers of science and technology have
fueled unsustainable global exploitation of earth’s resources leading to numerous
challenges within the food system (FAO 2010; UNDP 2016). In addition, the
increase in world population and the rapid urbanization have overloaded the food
system. The United Nations predicts that world population will increase by more
than 1 billion people within the next 15 years, reaching 8.5 billion in 2030. Of these,
the majority (66%) is forecasted to be living in cities by the year 2050 (UN 2015a).
These trends in combination with the growth in unhealthy eating habits and
nutrition-related disorders have made a new approach to food nutrition and agri-
literacy at school imperative.
The insights from the GBG project and the results from numerous interviews with
both teachers and students showed that the successful application of aquaponic
technology is dependent on the careful planning and maintenance of the system.
The digital version of the GBG – the eGBG – was developed to address these
challenges and to use the related opportunities in promoting digital literacy in school.
The idea of the eGBG takes inspiration from the idea of self-regulation in biological
systems. It is conceptually based on the idea of autopoiesis: referring to a system
capable of reproducing and maintaining itself. The term first introduced in 1972 by
biologists Maturana and Varela (1980) describes the self-maintaining chemistry of
living cells, and ever since then, the concept has been applied in a wide array of fields
such as cognition, systems theory, and sociology. In the eGBG study, illustrated by
the setup and components in Fig. 23.2, water quality, temperature, dissolved oxygen,
CO2, pH, ammonia, and nitrite content are measured with sensors using an elec-
tronic and digitalized setup, followed by appropriate automated regulation and
adjustments to the required or set levels. This system used alongside a basic
maintenance regime better enables children to learn Information and Communications
Technology (ICT), together with Science, Technology, Engineering, and Mathematics
(STEM) subjects in addition to a wider understanding of sustainable urban farming and
animal welfare practices. The eGBG minimizes human error and reduces the amount of
critical resources such as the physical labor and hours that would otherwise be required
for the care and maintenance of a balanced aquaponic system.
602 B. E. Mikkelsen and C. M. Bosire
Fig. 23.2 The experimental eGBG setup. The illustration shows the two parts of the system. The
aquaponic system itself and the measuring devices and the minicomputer used to follow the
biological condition of the eGBG system
23.3 Methods
In the context of this chapter, three data sources were used including (a) an explor-
atory study on the educational opportunities at school (Bosire et al. 2016), (b) a
feasibility study carried out among teachers (Bosire and Sikora 2017), and (c) the
eGBG study (Toth and Mikkelsen 2018).
The first study (a) was carried out as an exploration of the opportunities and
challenges of using aquaponics as an educational tool. The study aimed at investi-
gating to what extent it makes sense to use aquaponics in school teaching. Data from
three (N ¼ 3) independent qualitative interviews were collected. The informants
were (1) a biology teacher engaged in natural science teaching at primary school;
(2) a consultant entrepreneur, which is an aquaponic expert, too; and (3) one local
aquaponic bio-farmer. The data analysis procedure was inspired by the future
workshop approach (Jungk and Müllert 1987), leading to a categorization and
evaluation according to the three categories of critique, fantasy, and strategy.
In the second study (b), a feasibility study was carried out at the Blågaard Public
School located within the Copenhagen Municipality in cooperation with two biology
teachers and a physics teacher and with approval from the school administration. The
local aquaponic bio-farmer and expert was also involved. A low-cost aquaponic
facility for teaching was developed using a simple do-it-yourself (DIY) food pro-
duction system and off-the-shelf components. The idea for this design and construc-
tion was to illustrate that this kind of technology can readily be undertaken, and it is
not only for advanced urban growing but that it also has potential to be used as a
science-teaching tool in humbler settings such as a local school. Since the budget of
23 Food, Sustainability, and Science Literacy in One Package?. . . 603
the school is limited, the overall goal was to complete the project at low cost and to
carefully fit the system within the requirements of the existing curricula.
In the third study (c), a digital component was added to an improved version of
the aquaponic system and the eGBG was introduced. The eGBG is a learning
program based on simple aquaponics, and it is designed to create learning insights
among adolescents. The program’s special focus is on teaching principles of sus-
tainable food production in cities and at the same time to facilitate ICT learning. The
program’s didactics is aimed at showing how a biological system like aquaponics
can be controlled, maneuvered, and self-regulated using sensors and feedback
mechanisms. This is done by connecting sensors that measure temperature, pH,
and nutrient balance via a digital interface such as Arduino. The eGBG developed a
simple urban farming tool based on a learning package for schools where students
can learn about this technology in biology classes. By studying how the sensors
work, they have the ability to learn how ICT can be integrated to monitor and control
a living biological system.
The eGBG educational program can be used both in an interdisciplinary course
with ICT as a theme or in the subjects of biology, physics, and chemistry. The
components of the eGBG are for a low-cost aquaponic system that has been
developed for the school context as described previously. Some of the key elements
were supplied by BioTeket, which is a company with a social and cultural remit with
an emphasis on environmental technology. BioTeket offers a series of workshops
and events, giving the citizens of Copenhagen an opportunity to gain experience
with sustainable urban life. The assembly was done under the company’s technical
supervision. According to the national curricula, ICT in elementary school is taught
not as a stand-alone subject, but in a transversal manner spanning several subjects.
Combining smart and sensor-based control and biological system therefore seems
straightforward for this requirement. Urban farming technologies require a monitor-
ing system with a multitude of sensors since maintaining a system in balance
requires continuous measurement of temperature, pH, etc. To meet this requirement,
the eGBG was developed in cooperation between Aalborg University, a municipal
school in Albertslund, and the enterprise BioTeket. The development process was
configured as an action research study where data was collected along with the
development process.
1. From the first study, the findings showed that visions of a new way of teaching
with inclusion of the modern technology could be perceived as an advantage in
influencing transformational processes at school. Nevertheless, this process
requires some critical, practical, and theoretical considerations for implementa-
tion of the system to make it successful and sustainable in the long term. Some of
the positive issues from the users’ perspectives included a wide range of appli-
cation in the subjects of biology, mathematics, science, and more. Reduction
604 B. E. Mikkelsen and C. M. Bosire
pollution and efficient resource usage; flexibility of the system setup, e.g., on
rooftops; and the production of (organic-like*) twin products (fish and plant
foods). Potential limitations included time constraints, lack of financial resources,
as well as the need for frequent care and maintenance. (* In the EU, current
legislation provides that only vegetal produce grown in soil may be considered
“organic.” This is not the case, e.g., in the USA, where aquaponic produce can be
grown organically and legally sold as being organic.)
2. From the second study (b), the feasibility study, the experiences of the study
indicated that the learning concept, the overall idea, and the didactics fit well into
the educational curricula and also with the projects that the school had already
planned to undertake in the field of sustainability. The experience showed that
such teaching needs to be carefully planned well ahead of time. Furthermore, the
idea of a knowledge triangle approach, bringing service learning, university
research, a small enterprise, and the learning staff into an informal project and
innovation network, is a fruitful way of organizing the undertaking. In addition,
the initiative enjoys the support of the municipality that sees entrepreneurship and
innovative learning approaches as important objectives.
3. The third study (c), the eGBG study, showed that the school was supportive and
already had newly purchased sensors to measure pH, temperature, CO2, and
dissolved oxygen (DO). Therefore, the data could be conducted with minimal
new effort for training, as the teaching staff were already well prepared to collect
data digitally. The school, at the point of project startup, was already planning to
measure nitrate and ammonia using the sensors, since the basic concept of the
teaching was to increase knowledge, skill, and competency in relation to the
nitrogen cycle. The idea of creating aquaponic technology and applying it in the
teaching was readily accepted by the school since the neighboring school already
had that kind of an AP system up and running.
Acknowledgments Thanks to biology teachers Mette and Else at Blågård School in Copenhagen
Municipality, to Lilja Gunnarsdottir and the teachers at Herstedlund school, and to Inge Christensen
from the Nature Centre in Albertslund municipality. Thanks also to Viktor Toth, a student at
Integrated Food Studies, Aalborg University, for providing data from the eGBG study. Thanks also
to Tomasz Sikora and Kathrine Breidahl from the Integrated Food Studies that participated in the
fieldwork. Thanks also to the owner and CEO Lasse Antoni Carlsen of Bioteket, Copenhagen, for
providing components and guidance in developing the GBG program.
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the copyright holder.
Chapter 24
Aquaponics and Social Enterprise
24.1 Introduction
S. Milliken (*)
School of Design, University of Greenwich, London, UK
e-mail: S.Milliken@greenwich.ac.uk
H. Stander
Department of Animal Sciences (Division of Aquaculture), University of Stellenbosch,
Stellenbosch, South Africa
e-mail: hbs@sun.ac.za
incomes for landless and poor households. Domestic production of food, access to
markets, and the acquisition of skills are invaluable tools for securing the empow-
erment and emancipation of women in developing countries, and aquaponics can
provide the foundation for fair and sustainable socioeconomic growth (Somerville
et al. 2014). This chapter presents some examples of recent initiatives by social
enterprises using aquaponics.
produce all year-round, primarily using aquaponics. The company now employs a
number of individuals with autism spectrum disorder (ASD) and finds that the
scheduling, precision, and monitoring required in aquaponics perfectly match with
their skills (Fasciglione 2015). A core value of the business is to engage their
workforce through leadership training, active participation, and team building, and
provide them with the opportunity to gain new skills and competencies. Similarly,
the ACRES Project (Adults Creating Residential and Employment Solutions; https://
acresproject.org/aquaponics) in Pennsylvania uses aquaponics to provide horticul-
tural therapy, employment, and community integration for adults with autism and
intellectual disabilities. They are involved in all facets of the aquaponic system, from
care and maintenance to harvest and sales, and the scheduled procedures and daily
routines that aquaponics requires provide them with the stability and structure that
they find reassuring. By fostering social, vocational, and self-advocacy skills,
ACRES therefore uses aquaponics to help autistic individuals optimize their poten-
tial, develop practical life skills, increase social capacity, and transition to work and
independence.
The FabLab Nerve Centre in Northern Ireland has set up a social enterprise
aquaponic farm to teach people with learning difficulties entrepreneurial and digital
skills. Using state-of-the-art digital equipment, such as 3D printers, CNC routers,
and laser cutters, students will receive hands-on training and experience in a range of
digital design and making techniques that will allow them to design, build, and
operate an aquaponic farm. As part of the project, a newly created social enterprise
will be developed by the young people, allowing them to sell the produce from the
farm to local businesses, thereby developing their skills in social entrepreneurship,
business, and marketing (www.nervecentre.org/news/fablab-nerve-centre-launches-
aquaponic-digital-farm).
Solutions for Change, a social enterprise which is dedicated to solving family
homelessness, runs Solutions Farms in California (www.solutionsfarm.org). The
aquaponic farm provides training for homeless families in growing tilapia and
seasonal leafy greens and herbs, which are then sold to local restaurants, markets,
and schools. It functions as a laboratory for teaching important work values and
preparing people for re-entry into the workplace, thereby raising hope, as well as
produce.
Asociacíon Huerto Lazo (www.huertolazo.eu) is a social enterprise in the prov-
ince of Malaga, Spain, which offers internships to young people from troubled
backgrounds. The interns are given practical training in aquaponics in a safe
environment. The catfish, tilapia, and tench are sold to El Sollo restaurant in
Fuengirola (Fig. 24.1).
610 S. Milliken and H. Stander
Fig. 24.1 Aquaponic facilities at Asociacíon Huerto Lazo – anticlockwise from top left: catfish
tanks in the aquaponic greenhouse; tilapia tanks with Gynostemma pentaphyllum, which is sold for
medicinal purposes; the water filtration tanks at Huerto Lazo; Ulrich Eich demonstrating his
aquaponic system (Photographs: Sarah Milliken)
Food security exists when all people, at all times, have physical and economic access
to sufficient, safe, and nutritious food that meets their dietary needs and food
preferences for an active and healthy life (Allison 2011). There are four food security
pillars, which define, defend, and measure food security status locally, nationally,
and internationally. These are food availability, food accessibility, food utilization,
and food stability. Food availability is achieved when nutritious food is available at
all times for people to access, while food accessibility is achieved when people at all
times have the economic ability to obtain nutritious food available according to their
dietary preferences. Food utilization is achieved when all food consumed is absorbed
and utilized by the body to make a healthy active life possible, and food stability is
achieved when all the other pillars are achieved (Faber et al. 2011).
Urban and peri-urban agriculture are increasingly recognized as a means by which
cities can move away from current inequitable and resource-dependent food systems,
reduce their ecological footprint, and increase their liveability (van Gorcum et al.
2019; Dubbeling et al. 2010). On account of being almost completely dependent on
produce imported from other regions, urban consumers are particularly vulnerable to
24 Aquaponics and Social Enterprise 611
food insecurity. For those of low socioeconomic status, this dependence means that any
fluctuation in food prices translates into limited purchasing power, increased food
insecurity, and compromised dietary options. Community-based aquaponics enter-
prises offer a new model for blending local agency with scientific innovation to deliver
food sovereignty and food security, by re-engaging and giving communities more
control over their food production and distribution (Laidlaw and Magee 2016). If
implemented as a program to be managed by local people, aquaponic systems have
the potential to address food sovereignty. In turn, food security is boosted by consum-
ing the fish, which is a significant source of protein, essential amino acids, and vitamins.
Even when consumed in small quantities, fish can improve dietary quality by contrib-
uting essential amino acids, which are often missing or underrepresented in vegetable-
based diets.
British social enterprise Byspokes Community Interest Company (CIC) set up a
pilot aquaponic system and training program at the Al-Basma Centre in Beit Sahour,
Occupied Palestinian Territories (OPT), a region where availability of space for food
production is a serious problem, particularly in the urban areas and refugee camps.
Even in agricultural areas, land access is being lost through Israeli controls and
through effective annexation by the Israeli “Security Fence.” Aquaponics therefore
offers a water- and space-efficient solution to growing fresh, local produce, includ-
ing a high-quality protein source (fish), thereby helping to combat malnutrition and
food insecurity, while at the same time providing new opportunities for income
generation. 40% of the population in the OPT (25% in the West Bank) are classed as
“chronically food insecure”, and unemployment stands at around 25%, with highs of
80% in some refugee camps. From an economic viewpoint, the project demonstrated
that an aquaponic system could contribute significantly to household incomes and so
help lift families out of poverty, while also providing a range of fresh vegetables and
fish to families least able to afford such high-quality food (Viladomat and Jones
2011).
Since 2010, the Food and Agriculture Organization (FAO) of the United Nations
has been implementing an Emergency Food Production Support Project for poor
families in the Gaza Strip, where 11 years of Israeli sea, land, and air blockade,
combined with low rainfall resulting in drought, have severely compromised the
possibilities for domestic food production in one of the most densely populated areas
of the world. With so many restrictions, fresh vegetables are expensive and hard to
find. 97% of the Gaza Strip population are urban or camp dwellers and therefore do
not have access to land. Poverty affects 53% of the population, and 39% of families
headed by women are food insecure. Enabling families to produce their own
affordable fresh food is therefore a highly appropriate and effective response to the
current situation. Food-insecure female-headed households living in urban areas
were given rooftop aquaponic units, and other units were installed in educational
and community establishments. Having an aquaponic unit on their roof means that
the women can simultaneously improve their household food security and income
while still taking care of their children and homes. All of the beneficiaries have
increased their household food consumption as a result (FAO 2016).
612 S. Milliken and H. Stander
Fig. 24.2 Some illustrations of INMED’s Community Projects in South Africa. (Photographs
supplied by Janet Ogilvie from INMED)
wicking beds) are placed in communities, which adopt them, and initial training for
tunnel care watering and fertilizing techniques is given. An aquaponic system was
commissioned at one of the projects, in Kommetjie, Cape Town.
Issues of food security and food sovereignty are not only pertinent to the
developing world. In Seville, Spain, social enterprise Asociacíon Verdes del Sur
has set up an aquaponic greenhouse in the grounds of a school in Polígono Sur, the
most socially deprived part of the city which is characterized by long-term unem-
ployment and a high incidence of drug-related crime. The aquaponic unit is used as
part of an environmental education program for local residents, including teaching
the benefits of eating locally grown fresh food and developing skills for the unem-
ployed (http://huertosverdesdelsur.blogspot.com). A prototype domestic unit has
also been set up in the house of one of the local residents, Soledad (Fig. 24.3).
The Well Community Allotment Group (Crookes Community Farm) is a social
enterprise run by volunteers in Sheffield, UK, that is on a mission to connect the local
community with their food by actively involving them in its production, and
by educating them about the benefits of local food. In 2018, the association was
awarded an Aviva Community Fund Award in order to build an aquaponic unit which
will be used to educate individuals, schools, youth groups, and other organizations
(https://www.avivacommunityfund.co.uk/voting/project/pastwinnerprojectview/17-
6291).
614 S. Milliken and H. Stander
Fig. 24.3 Aquaponic facilities in Polígono Sur – anticlockwise from top left: the aquaponic
greenhouse at the school; Soledad with a frozen tilapia raised in her domestic unit; tomatoes and
an aubergine saved for their seeds; the domestic aquaponic unit. (Photographs: Sarah Milliken)
In the United States, a number of social enterprises using aquaponic systems have
been set up across the country as part of a growing social movement focusing on
using urban agriculture to increase food security and community cohesion. One of
the first was Growing Power, which was founded by Will Allen in 1995, with the
objective of using urban agriculture as a vehicle for improving food security in
central Milwaukee and for the long-term strengthening of its neighborhoods, and to
give inner-city youngsters an opportunity to gain life skills by cultivating and
marketing organic produce. Growing Power provided facilities or land, guidance
in food growing, and overall project maintenance, and the produce was either
donated to meal programs and emergency food providers or sold by the youngsters
at local farm shops and farmers’ markets, with the stipulation that one-quarter of the
proceeds be returned to the local community (Kaufman and Bailkey 2000). By all
accounts, Growing Power was doing exactly what they had set out to do: they were
feeding, training, and exposing thousands of people to a more autonomous relation-
ship with their food. But while their mission was being fulfilled, it carried significant
costs. More money was exiting than entering Growing Power’s doors, and by 2014,
the social enterprise had a debt of more than $2 million (Satterfield 2018). Faced
with insurmountable debt and legal pressure, Growing Power was eventually
dissolved in 2017. However, the legacy of the enterprise lives on in the form of
24 Aquaponics and Social Enterprise 615
other social ventures that were inspired to start similar initiatives. One such venture
which acknowledges Will Allen’s influence is the Rid-All Green Partnership in
Cleveland, Ohio, whose mission is to educate the next generation to not only learn
to grow and eat fresh foods but also to operate and grow their own businesses in the
food industry, ranging from selling fresh produce and fish to food distributors to
processing and packaging fresh food products (https://www.greennghetto.org).
The urban agriculture movement in the United States has been fuelled by the US
Department of Agriculture (USDA) Community Food Project (CFP) competitive
grant program, which was established in 1996 with the aim of fighting food
insecurity through the development of community food projects that promote the
self-sufficiency of low-income communities. Since 1996, this program has awarded
approximately $90 million in grants. One social enterprise which has benefited from
this scheme is Planting Justice (www.plantingjustice.org) which built an aquaponic
system on a vacant lot in East Oakland, California, which is run by former prison
inmates. Twelve living wage jobs have been created, 5000 pounds (2268 kilos) of
free produce has been given to the community, and the project has put $500,000 in
wages and $200,000 in benefits back into the neighborhood (New Entry Sustainable
Farming Project 2018).
The GrowHaus (https://www.thegrowhaus.org) was founded in 2009 as a social
enterprise, which focuses on healthy, equitable, and resident-driven community food
production; 97% of the food consumed in Colorado is produced out of state, and the
neighborhood where The GrowHaus is located has been designated a “food desert”
based on characteristics of low income, race/ethnicity, long distance to a grocery
store, lack of access to fresh affordable food, and dependence on public transporta-
tion. The residents have come to rely on fast food, convenience stores, petrol
stations, and food banks for the majority of their food staples. Due to these factors,
many people face significant challenges in terms of food security and access,
resulting in dramatic increases in related health issues. Initially in partnership with
Colorado Aquaponics (www.coloradoaquaponics.com), and since 2016 indepen-
dently, the GrowHaus operates a 3200 square foot (297 square meter) aquaponic
farm, and the produce is sold through a weekly farm fresh food basket program at a
price point comparable to Walmart, as well as to restaurants, with a portion donated
to the local community. To help the transition to healthier eating, the GrowHaus also
organizes free training and community events focused around food. In the
2016–2017 fiscal year, the GrowHaus generated an income of $1,204,070, of
which $333,534 was earned income, and $870,536 was raised through government
grants, charitable foundations, corporate contributions, and individual donations.
With operating costs of $934,231, the net annual income was $269,839 (https://
www.thegrowhaus.org/annual-report).
Trifecta Ecosystems (formerly Fresh Farm Aquaponics; http://trifectaecosystems.
com) was founded in 2012 in Meriden, Connecticut. Their mission is to address
urban food security by creating incentives for communities to grow their own food
while also raising awareness about sustainable farming through education, work-
shops, and city projects. The enterprise employs six staff who provide aquaponic
systems to organizations for educational purposes, workforce development,
616 S. Milliken and H. Stander
The examples above illustrate some of the different business models adopted by
aquaponics social enterprises. Whether they will continue to thrive and grow or, like
Growing Power, ultimately fail, remains to be seen. In the case of Growing Power,
potential reasons for its collapse include Will Allen’s inability to empower and retain
an operational management team, and a lack of oversight by board members, which
compromised the organization’s financial health (Satterfield 2018). An in-depth
analysis of two aquaponics social enterprises conducted in 2012–2013 revealed
four distinct factors what were significant to their survival (Laidlaw and Magee
2016). Sweet Water Organics (SWO) began as an urban aquaponic farm in a large,
disused, inner city industrial building in Milwaukee in 2008. It was funded primarily
by its founders in order to develop creative capacity, employment opportunities, and
chemical-free, fresh, and affordable food for the local community. In 2010, a new
organization, Sweet Water Farms (SWF), was split from SWO, with the idea that
they would grow as a mutually supportive, cohesive hybrid organization, including
both a for-profit commercial urban farm (SWO) and a not-for-profit aquaponics
“academy” (SWF). SWF managed volunteer operations and hosted training and
education programs at the Sweet Water urban farm, while developing programs on a
local (Milwaukee and Chicago), regional, national, and international scale. Sweet
24 Aquaponics and Social Enterprise 617
Water had a loyal following among local restaurateurs and fresh food stores for its
lettuce and sprouts produce, and sold its fish to a single wholesaler. However, the
hybrid not-for-profit/for-profit enterprise model proved to be challenging, as both
sides of the organization struggled to identify their role in relation to the other. While
each side had a different structure relating to their operational character, and
although their operations frequently overlapped, their strategic planning and visions
sometimes did not. After 3 years of operation, SWO had still not managed to make a
profit, and in 2011 the Milwaukee municipal government awarded a $250,000 loan
on condition that 45 jobs would be created by 2014. In October 2012, SWO had
11–13 permanent employees, but was still being sustained through loans financing
and equity investment. By June 2013, as loan repayments fell due and the job
creation targets were not met, the for-profit arm of Sweet Water went into liquida-
tion, and SWF took over as the primary operator of the Sweet Water urban farm.
Currently, SWF operates entirely as an educational and advisory enterprise run by
volunteers and a small team of part-time employees, and no longer supplies restau-
rants with produce (Laidlaw and Magee 2016).
The Centre for Education and Research (CERES) in Melbourne, Australia,
opened its aquaponics facility in 2010. The system was designed as a suboptimized
commercial system with the production capacity to support a single wage for the
farmer who maintains it. This wage varies based on how much he/she produces, with
the vegetables being sold through the CERES Fair Food organic box delivery
service. The scale of the operation does not generate a return that would permit the
setting up of a fish-processing facility. Stakeholders at Sweet Water Farms and
CERES identified that the principal factor behind their survival was ongoing com-
mitment, in the form of continued support of personnel with technical and business
management skills combined with an enduring leadership, and the willingness of the
stakeholders to remain involved and prepared to cooperate without strong financial
incentives. The second factor was the local political context. While the city of
Milwaukee supported Sweet Water both through policy initiatives and direct finan-
cial aid, which allowed it to expand its fixed assets and human resources, build
market awareness, and acquire a sizeable regular commercial customer base, the
CERES project had little such support, beyond an initial grant, and it had struggled
to generate revenue, which would have allowed it to expand. Costs of compliance
and licensing also made it difficult to engage with local markets in more than a token
way, which dampened its motivation to market and sell the produce, and made it
untenable for the operation to develop beyond a small part-time income-generating
enterprise. The third factor was the availability of markets for urban aquaponics
produce. While urban aquaponics is attractive to a customer base that is increasingly
responsive to issues of food security and ethical consumption, such as in Milwaukee,
this was not the case in Melbourne. The final factor was diversification. Both CERES
and SWO/SWF benefitted from translating social and technical experimentation into
a range of training and educational services. SWO/SWF, being a larger concern,
obviously had greater capacity for developing these services, and these proved vital
in sustaining the social enterprise when commercial plans failed to materialize
(Laidlaw and Magee 2016).
618 S. Milliken and H. Stander
24.5 Conclusions
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Open Access This chapter is licensed under the terms of the Creative Commons Attribution 4.0
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adaptation, distribution and reproduction in any medium or format, as long as you give appropriate
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The images or other third party material in this chapter are included in the chapter’s Creative
Commons licence, unless indicated otherwise in a credit line to the material. If material is not
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statutory regulation or exceeds the permitted use, you will need to obtain permission directly from
the copyright holder.