Journal of Applied Phycology (2024) 36:1987–2004
https://doi.org/10.1007/s10811-024-03220-2
REVIEW
Suspended filamentous algal cultures for wastewater treatment:
A review
F. Sabatte1 · R. Baring1 · H. Fallowfield1
Received: 2 November 2023 / Revised: 23 February 2024 / Accepted: 23 February 2024 / Published online: 18 March 2024
© The Author(s) 2024
Abstract
More than 50 years have passed since the first studies of microalgae treating effluents were published. Suspended growth
of filamentous algae in wastewater ponds has been considered in several publications for over a decade. However, despite
all the research efforts and the knowledge generated, the technology is far from being adopted. This review compiles all the
publications identified in different databases, which used filamentous algal ponds to remediate varied wastewaters, with the
aim of identifying the research needs to allow the technology’s application. The experimental methods and results obtained
were extracted and compiled for comparison from 28 relevant studies, in which municipal wastewater and Oedogonium
spp. were most used. Most of the studies were performed at a small laboratory scale and for short time periods. There was
a remarkable use of effluents with a high degree of pretreatment and more studies focused on the biomass productivity than
the treatment performance. It is recommended that future research use wastewater, with minimum intervention, rather than
defined nutrient solutions, to assess the potential for wastewater treatment. Transitioning from laboratory to outdoor systems
at scale should be a primary aim to further adopt this technology.
Keywords Effluent · Filamentous algal ponds · Phycoremediation · Wastewater treatment · Bioremediation
Introduction
Wastewater treatment using algal cultures is a field that has
many decades of history, yet it still must overcome many
bottlenecks to reach an extended application. High-rate algal
ponds are a proven, effective microalgal treatment technology (Young et al. 2017; Fallowfield et al. 2018), however,
there is still potential for improvement. The application of
microalgae for wastewater treatment predominates in data in
current studies, which to meet discharge standards requires
biomass removal, contributing to a high percentage of both
the economic and energetic final cost of the process (Acien
et al. 2016). Therefore, cost-effective removal methods are
needed to enhance this technology’s application. There are
* F. Sabatte
felipe.sabatte@flinders.edu.au
R. Baring
ryan.baring@flinders.edu.au
H. Fallowfield
howard.fallowfield@flinders.edu.au
1
College of Science and Engineering, Flinders University,
GPO Box 2100, Adelaide 5001, South Australia
studies, which evaluate alternative methods for the separation of microalgal biomass from the treated wastewater (Park
et al. 2019; Chu et al. 2021; Young et al. 2021). In contrast,
there has been less focus on application of filamentous algae
to merge wastewater treatment with biomass production
(Lawton et al. 2017). Compared to microalgae, filamentous
algae offer the advantage of facilitating biomass separation
that would reduce the cost and complexity of the technologies employed, lowering both the capital and operational
expenditures (CAPEX and OPEX respectively) of potential
projects employing this technology. However, there are still
many research needs to address before adoption of freshwater filamentous algae for wastewater treatment (Liu et al.
2020; Rearte et al. 2021), especially regarding large scale
outdoor validation, the effect of nutrient loading, operational
parameters and other aspects that will be reviewed here.
There are already some successful systems utilising
filamentous algae, consisting of inclined planes where a
matrix supports attached growth, often known as algal turf
scrubbers (ATS) (Mulbry et al. 2010), which are already
commercialized. Numerous studies have been conducted
with these types of devices, which have also identified specific challenges to that approach (Blersch et al. 2013). This
Vol.:(0123456789)
1988
review, however, will not include ATS given that it is considered these are designed to treat specific wastewater types
(WW). Furthermore, the short hydraulic retention time of
ATS would be insufficient for many filamentous algae to
effectively remove nutrients or contaminants from more concentrated effluents.
This review provides a state-of-the-art overview of wastewater treatment using filamentous algae growing suspended
in various wastewater matrices. The studies and findings
were compared and discussed when considering: the type
of wastewater used and the degree of pretreatment received,
the filamentous algae employed and their performance, and
the environmental conditions in which those studies were
conducted. The review also identifies the research needed
to further the application and adoption of filamentous algae
for wastewater treatment.
Methods
A literature review was conducted using the keywords “filamentous algae”, “macroalgae”, “wastewater”, “wastewater
treatment” and “HRAP” in Scopus, ScienceDirect, Taylor
& Francis Online, SpringerLINK and Wiley Online Library.
The criteria to incorporate publications into this review were
as follows: (1) the studies must have been conducted with
filamentous algae suspended in the matrix, (2) the studies
must have assessed filamentous algae growth or nutrient
removal in the matrix, (3) at least one of the goals must
have been to build knowledge towards wastewater treatment
(WWT) systems. An exemption was made to include the
study performed by Kim et al., (2018) because, despite the
filamentous algae growing attached to the sand bottom, the
biomass was spread across the water column and the depth
and operational parameters of the pond were more similar
to HRAPs than biofilm filters or ATSs. The references cited
in the articles retrieved on the first search were also interrogated for other relevant articles. The data were collated
to enable detailed review of the ‘state of the art’ of the field
and identify future research needs. Note that the data was
organised by case study, hence there were publications with
more than one reported study.
Wastewater types and their manipulation
A wide spectrum of effluents was utilised in studies reporting
the performance of filamentous algae for WWT. This range
could be partitioned in to three groups by their contaminant
type. The first one being wastewater with high organic load,
where nitrogen, phosphorus and carbon can be a problem
if released in the environment without adequate treatment
(e.g., triggering eutrophication processes). The second
group could be those containing metals or metalloids. Heavy
Journal of Applied Phycology (2024) 36:1987–2004
metals are toxic even at very low concentrations, which are
often surpassed by industrial effluents. Finally, the organic
pollutants group, which are basically organic substances
toxic or harmful to humans, flora and fauna.
The most represented WW in this review belong to the
first group - high organic load, where 19 out of 28 studies
were carried out using effluents with the goal of lowering
the N, P and C concentrations. Municipal WW was the most
common effluent in this group (13 experiments were conducted with WW from this origin) (Yun et al. 2014; Cole
et al. 2016; Neveux et al. 2016; Ge et al. 2018; Min et al.
2019; Piotrowski et al. 2020; Lawton et al. 2021; Kube et al.
2022), combined with a high variety of pre-treatment processes. Some effluents went through a settling and screening process only (Neveux et al. 2016), in most studies the
wastewater was collected from a later treatment stage at the
WWTP (Yun et al. 2014; Cole et al. 2016; Neveux et al.
2016; Ge et al. 2018; Lawton et al. 2021; Kube et al. 2022),
some studies used the final effluent of the WWTP and performed further conditioning in the laboratory such as UV
sterilization or autoclaving (Ge et al. 2018; Min et al. 2019;
Piotrowski et al. 2020). The remainder of the studies used
effluents from different industries or activities such as piggeries, slaughterhouses, rural runoff, and aquaculture (Saunders et al. 2012; Roberts et al. 2013, 2015, 2018; Wang et al.
2013; Cole et al. 2014, 2015; Ellison et al. 2014; Kim et al.
2018; Tan et al. 2018; Tabinda et al. 2019; Valero-Rodriguez
et al. 2020; Rearte et al 2021; Ali Kubar et al. 2022; Liu
et al. 2023) Table 1 and 2.
It is worth noting that two experiments (Valero-Rodriguez et al. 2020; Liu et al. 2023), purporting to explore
distinct aspects of WW treatment/nutrient recycling used
synthetic growth media. Even if the intention were to simulate the N, P, C load of an effluent, this is a questionable
approach, given the heterogeneity which characterizes most
wastewaters.
Conventional wastewater treatment plants (WWTP) have
various stages of treatment where the effluents get progressively treated until the desired standards of quality are met.
One of the aims of utilising filamentous algae is to replace as
many steps as possible of the conventional treatment without
sacrificing the final quality of the treated wastewater. The
effluents used in the studies reviewed had a variety of pretreatment processes, however, some lacked detail regarding
treatment and effluent composition, for example merely noting that “secondary treated effluent” was used in the study.
The detailed reporting of any pre-treatment and subsequent
composition of influents used in studies investigating the
performance of algae for wastewater treatment should be
encouraged.
Wastewater treatment processes may be designed for
a myriad of situations, each with specific conditions and
operational requirements. This approach could explain the
-
Unknown, diluted
Settled
Water treatment residuals
-
Synthetic growth medium
Synthetic growth medium
Settled and screened
Slaughterhouse effluent
Textile industry effluent
Digested and diluted
Settled, filtered and settled
Piggery effluent
Piggery effluent
Screened and settled
Screened and settled
Municipal
Primary, Secondary, Diluted centrate,
Autoclaved
Municipal
Municipal
Primary, Secondary, Autoclaved
Primary, Secondary, Autoclaved
Municipal
Municipal
Primary and secondary treatment
Primary and secondary treatment
Municipal
Aeration, filtering, UV disinfection,
wetland
Municipal
Municipal
Fully treated
Fully treated and autoclaved
Municipal
Municipal
5-stage Barden Pho process
Fully treated
Municipal
Municipal
-
Fully treated, 10 µm filtered and UV
sterilized
Contaminated rural streams
Municipal
-
-
Ash water
Ash water
-
10 μm filtered
Ash water
Reed beds, settled and sand filtered to
150 μm
Aquaculture effluent
Ash water
Filtrated, centrifuged, and 0.45 μm filtered
Reed beds, settled and sand filtered to
150 μm
ABS industry effluent
Aquaculture effluent
Previous treatment
Wastewater
Yes
Yes
Yes
Yes
Yes, flue gases
Yes
Yes
Yes
CO2 injection
Yes
Yes
-
-
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Nutrient amendment
nr
nr
-
-
61 NH4-N
486
65.5
41.2
27.2
16.06
10.7
10.7
20.4
23.75 TDN
19.5 DIN
9.9
3.18
1.12
5.3 DIN
95.65
2.85
nr
nr
nr
nr
2.62
2.34
40
TN mg L-1
nr
nr
-
-
5.9 DRP
149
6.2
6.7
5.04
0.63
1.47
1.47
3.5
6.77
4.3 DRP
0.6
0.92
0.23
2.6 DRP
nr
0.31
nr
nr
nr
nr
0.56
0.35
12
TP mg L-1
nr
1,140
-
-
291 TOC
1,474
90.7
53
31
10.26
14
14
nr
27.5 dissolved C
nr
13.4
nr
12
nr
nr
2.7
nr
nr
nr
nr
nr
nr
288
COD mg L-1
Roberts et al. (2018)
Tabinda et al. (2019)
Liu et al. (2023)
Valero-Rodriguez et al.
(2020)
Rearte et al. (2021)
Tan et al. (2018)
Wang et al (2013)
Neveux et al. (2016)
Neveux et al. (2016)
Ge et al. (2018)
Ge et al. (2018)
Ge et al. (2018)
Yun et al. (2014)
Kube et al. (2022)
Lawton et al. (2021)
Min et al. (2019)
Cole et al. (2016)
Neveux et al. (2016)
Lawton et al. (2021)
Piotrowski et al. (2020)
Kim et al. (2018)
Ellison et al. (2014)
Saunders et al. (2012)
Roberts et al. (2015)
Roberts et al. (2013)
Cole et al. (2015)
Cole et al. (2014)
Ali Kubar et al. (2022)
Reference
Table 1 Characterization and manipulation of wastewaters included in studies investigating the application of filamentous algae to wastewater treatment, where C, carbon; DIN, dissolved inorganic nitrogen; DRP, dissolved reactive phosphorus; TDN, total dissolved nitrogen; TOC, total organic carbon and NH4-N, nitrogen as ammonium, nr, not reported
Journal of Applied Phycology (2024) 36:1987–2004
1989
1990
range of pre-treatments used since, based on the specific
situation, filamentous algal treatment could be employed at
different stages within the treatment train. Of the 26 studies conducted with ‘real’ WW, seven reported working with
effluents, which had received three steps of conventional
treatment, and six studies performed a sterilization in the
laboratory (UV disinfection or autoclaving). Sterilisation
will obviate any interaction between the metabolic activity
of the algae and the effluent’s microbial load. Furthermore,
most of the pathogens would have been filtered out or eliminated in the sterilization stages before the algae could perform any treatment (Cole et al. 2016; Neveux et al. 2016; Ge
et al. 2018; Min et al. 2019; Piotrowski et al. 2020; Lawton
et al. 2021). Sterilization in the laboratory and other experimental procedures e.g., 0.45 μm filtration (Ali Kubar et al.
2022) are impracticable at scale and unlikely to be adopted
at wastewater treatment plants. Such interventions highlight,
when determining a study design, the importance of an
awareness of the potential operating conditions under which
the potential filamentous algae are required to perform.
To be able to compare the performance of different WW
systems it is necessary to know the initial composition of the
wastewater. Surprisingly one reviewed study carried out with
‘real’ wastewater did not report the initial values of C-N-P
(Piotrowski et al. 2020). The concentrations of nitrogen,
phosphorous and COD vary widely between influents used
to investigate the application of filamentous algae to wastewater treatment. The reported values of different species of
nitrogen and phosphorus from thirteen studies using ‘real’
municipal WW (Yun et al. 2014; Cole et al. 2016; Neveux
et al. 2016; Ge et al. 2018; Min et al. 2019; Piotrowski et al.
2020; Lawton et al. 2021; Kube et al. 2022)) were transformed into concentrations of TN and TP and are, together
with COD, shown in Fig. 1a. As can be seen, the TN ranges
from a maximum of 41.2 mg TN L
-1 for an effluent that only
had screening and settling stages as pre-treatment (Neveux
et al. 2016), to 1.12 mg TN L
-1 for an effluent reported to be
“fully treated” (Neveux et al. 2016). The maximum and minimum TP concentration reported were measured in the same
-1. Regarding
WWs respectively, at 6.7 mg L
-1 and 0.23 mg L
the COD, the effluent used by (Neveux et al. 2016) presented
the highest value at 53 mg COD L
-1, while the lowest value
was reported by (Ge et al. 2018) at 10.26 mg COD L
-1, for
municipal WW with primary and secondary pre-treatment
stages followed by dilution and autoclave sterilization.
Across various studies reviewed there was a large variation of concentrations of TN, TP, and COD between effluents from different industries (Fig. 1b). Tan et al. (2018)
reported the highest values of the measured parameters in
piggery wastewater; 486 mg TN L
-1, 149 mg TP L
-1 and
-1
1474 mg COD L
. In contrast, Cole et al. (2015) reported
the lowest initial values of nitrogen for aquaculture effluent;
at 2.62 mg TN L
-1 and Kim et al. (2018) reported the lowest
Journal of Applied Phycology (2024) 36:1987–2004
phosphorus concentration in rural stream water; at 0.56 mg
TP L -1. However, there is still disparity across studies that
clearly demonstrates the need to report the composition of
the effluent used in the respective studies to enable adequate
comparison of treatment performance (Fig. 1).
Almost a third of the experiments reported supplementing the wastewater with C
O2 through a sparging system
(Roberts et al. 2013, 2015, 2018; Cole et al. 2014; Ge et al.
2018; Piotrowski et al. 2020; Rearte et al. 2021; Ali Kubar
et al. 2022), in some cases the gas addition was at fixed rates
and in others it was managed through pH control (Fig. 2).
Employed as a strategy even in full scale HRAPs (Acién
et al. 2016), the injection of C
O2 as an inorganic carbon
source would be acceptable when the availability of assimilable inorganic carbon is limiting for photosynthesis (i.e.,
as in the case of some synthetic media). However, effluents
with high organic load already have a generous concentration of organic carbon, which via microbial respiration can
be converted to inorganic carbon available for photosynthesis. Further, this process contributes to one of the desired
effects of the treatment process by lowering the organic
carbon concentration, supplementing C
O2 could partially
inhibit the aerobic metabolization of the organic carbon of
the effluent, which is in the core of the biological treatment
of WW.
More consideration should be given to the feasibility of
upscaling experimental processes incorporating CO2 addition to operational wastewater treatment systems. Specifically, the source of the gas supply and the infrastructure
necessary to supplement the wastewater. Both of thse also
have implications for increases in CAPEX and OPEX of the
potential projects.
Flue gases may be a source of C
O2 for injection, including power stations using fossil fuels, noting that the outcome would contribute to carbon sequestration into biomass,
reducing greenhouse gases emissions. This would require
the wastewater treatment plant and the source of CO2 to be
in proximity, which may be a significant constraint. Furthermore, establishing a wastewater treatment system, which
requires access to CO2 generated from combustion of fossil
fuels should not be considered a sustainable option. Furthermore, it is currently inconclusive whether the use of flue
gases in algal cultures enhances biomass productivity and
nutrient removal. Roberts et al. (2015) reported the outcome
of using the flue gases from a coal-fired power station. Their
results indicate that the C capture was negligible relative to
the power station emissions and the growth rates achieved by
the filamentous algae in the outdoor system were similar to
cultures without CO2 injection at smaller scales. These conclusions are similar to those of Young et al. (2019) using the
CO2 recovered from biogas scrubbing in pilot scale, outdoor
microalgal HRAPs. Neither the wastewater treatment performance nor biomass production was significantly enhanced
Journal of Applied Phycology (2024) 36:1987–2004
by the gas injection. The perspective of designing alternative, sustainable WWT systems that have lower environmental impact and rely on biological processes powered by solar
energy is less attractive if they require added consumables.
Additional nutrients either as separate salts or growth
media mixes were added to 25 % of the experimental systems in studies in this review. In this subgroup there were
four studies treating ash water (Saunders et al. 2012; Roberts
et al. 2013, 2015; Ellison et al. 2014), one using water treatment residuals containing high concentrations of aluminium
(Roberts et al. 2018) and one remediating textile industry
effluent (Tabinda et al. 2019). These effluents were amended
because they did not contain enough C, N and P to support
the algal growth. It is worth noting that the rationale in these
cases was to supplement the WW with nutrients to enable
filamentous algae to grow and sequester the metals intracellularly, followed by algal harvesting and extraction with the
biomass.
Similarly, Kube et al. (2022) used municipal WW that
had received primary and secondary treatment in a conventional WWTP and rather than using an effluent with
high nutrient content, they subsequently added nutrients
to maintain initial concentrations of 21 mg TN L
-1 and 5
-1
mg L of phosphate. Kim et al. (2018) also amended the
inlet water with nutrients intending to treat contaminated
water from rural streams. The practical utility of amending wastewater with nutrients to enable algal growth is
unclear. The practice increases the concentration of what
are normally target contaminants for removal, requires a
source of nutrients that have competing value for food
production and poses the question whether the use of algae
is an appropriate treatment option.
An additional aspect of the pretreatment to consider is
the dilution of effluents. This strategy was employed in
three studies (Wang et al. 2013; Ge et al. 2018; Tabinda
et al. 2019) to lower the potential toxicity of certain contaminants, especially ammonia, with freshwater. This practice raises two issues, firstly, the potential WWTP would
require the use of increasingly scarce, good quality water
to treat contaminated effluents. Alternatively, effluents
with lower concentrations of N-P could be considered for
the dilution. Dilution also increases the volume of wastewater requiring treatment increasing the size of the facility
required for treatment using filamentous algae. Ge et al.
(2018) conducted experiments with 50 times diluted centrate from municipal WW and 5-fold diluted secondary
treated municipal WW. Tabinda et al. (2019) performed
studies on textile industry WW, which had to be diluted
7 to 20-fold. The digested piggery effluent used by Wang
et al. (2013) was diluted 5 to 25-fold. The volume of the
treatment pond would increase equivalent to the dilution
factor compared with the undiluted effluent for the same
hydraulic retention time.
1991
However, the dilution of effluents may be justifiable at
the beginning of a study, as in the case of batch cultures
used to explore the dynamics of a potential continuous system. The rationale being that once a pond is stable at the
applied hydraulic retention time and the exchanged volume
is relatively small, dilution of the wastewater at the inlet
will occur given that nutrient concentrations in the pond are
likely reduced by algal growth. Another situation in which
dilution of the wastewater is necessary is when determining the algal tolerance thresholds to nutrients or chemical
concentrations. In order to assess the feasibility of algal
treatment for some types of wastewaters it is necessary to
know the upper and lower tolerance limits to the nutrients
and contaminants within the influent. In any case, diluting
the wastewater should be a strategy only applied at the early
exploratory stages of the design of an algal based treatment
process, and avoided in full scale WWTP operation.
Wastewater Treatment by Filamentous Algae
Chlorophyceae was the most common class of filamentous
algae used for wastewater treatment (WWT) systems, with
a single genus Oedogonium being used in 75 % of the studies (Fig. 3). It is worth noting that more than a third of all
the published studies (Saunders et al. 2012; Roberts et al.
2013, 2015, 2018; Cole et al. 2014, 2015, 2016; Ellison et al.
2014; Neveux et al. 2016; Valero-Rodriguez et al. 2020)
were carried out by the MACRO group at James Cook University (Australia), which worked specifically with Oedogonium species, consequently skewing the data. Nevertheless,
Oedogonium has been consistently identified as a suitable
candidate for wastewater treatment by other studies (Wang
et al. 2013; Yun et al. 2014; Tabinda et al. 2019; Piotrowski
et al. 2020; Lawton et al. 2021; Rearte et al. 2021; Kube
et al. 2022; Liu et al. 2023). Genera not within the Chlorophyceae were also included in this review given that the
aim of this work was to compare the results of suspended
growth systems using algae growing as filaments. Depending on the authors, these are referred to either as macroalgae
(Kube et al. 2022) or microalgae (Tan et al. 2018), the debate
regarding which term is more appropriate is out of the scope
of this review.
Across all studies, the biomass productivity (Fig. 4) was
expressed either by volume (g L
-1 day-1) or by surface area
−2
−1
(g m day ). Apart from 4 studies, which did not report
the productivity (Wang et al. 2013; Ellison et al. 2014; Tan
et al. 2018; Tabinda et al. 2019), the results ranged from 0.11
g DW m
-2day-1 for a Spirogyra culture treating municipal
WW (Ge et al. 2018) to 40 g DW m−2 day−1 for a Spirogyra pond treating water from contaminated rural streams
amended with nitrogen and phosphorus (Kim et al. 2018).
As can be seen in Fig. 4, Oedogonium is not only the genus
Hydrodiction,
Rhizoclonium,
Oedogonium
Oedogonium
Ash water
2.85 - 0.6 (80)
40 g m−2 day−1
Spirogyra
Municipal
Municipal
2.17 to 2.9 g m−2 10.7 - 0.9 (91.1)
day−1
2.92 to 4.03 g
10.7 - 0.4 (96)
m−2 day−1
3.37 g m−2 day−1
19.5 - 2.9 (85)
DIN
23.75 - 7.1 (70)
TDN
-
9.9 - 3.9 (60)
3.18 - 2.4 (36)
5.3 - 0.05 (99)
DIN
-
-
-
-
-
-
3.03 to 15.31 g
m−2 day−1
Oedogonium,
4.8 to 8.1 g m−2
Klebsormidium
day−1 AFDW
Oedogonium
6.3 to 9.2 g m−2
day−1
Oedogonium
8.9 to 15.8 g m−2
day−1
Hydrodiction
4.34 to 5.81 g
m−2 day−1
Oedogonium,
4.1 to 8.2 g m−2
Klebsormidium
day−1 AFDW
Oedogonium
0.102 g L-1 day-1
Oedogonium
Spirogyra
Oedogonium,
Spirogyra,
Ulothrix,
Vaucheria
Spirogyra
Municipal
Municipal
Municipal
Municipal
Municipal
Municipal
Municipal
Contaminated
rural streams
Municipal
Ash water
Oedogonium
Ash water
-
1.47 - 0.6 (60)
1.47 - 0.7 (51.2)
-
4.3 - 1.7 (60)
DRP
6.77 - 0.7 (90)
0.6 - 0.15 (74)
0.92 - 0.3 (65)
2.6 - 1.3 (50)
DRP
-
-
0.31 - 0.06 (81)
-
-
-
-
Oedogonium
Oedogonium
0.35 - 0.29 (16)
without CO2
-
3.8 to 23.8 g m-2
day-1
23.9 to 35.7 g
m−2 day−1
6.8 to 22.5 g m−2
day−1
2.9 to 8.2 g m−2
day−1
0.040 to 0.059 g
L-1 day-1
Oedogonium
2.3 - 0.9 (61)
without CO2
2.6 - 0.03 (99)
12 - 0.1 (99)
0.267 g L-1 day−1 40 - 4 (90)
TPi - TPf
(% Removal)
Tribonema
TNi - TNf
(% Removal)
ABS industry
effluent
Aquaculture
effluent
Aquaculture
effluent
Ash water
Productivity
(DW)
Genera
Wastewater
-
-
-
27.5 - 0.3 (99)
DIC
-
-
-
-
-
-
-
Trace elements
-
-
-
-
Trace elements
-
-
-
Not assessed
-
Not assessed
Pathogen
removal
-
-
Not assessed
Not assessed
Not assessed
Not assessed
-
Not assessed
Not assessed
Not assessed
Not assessed
-
Al and Zn below regulatory level
Trace elements
-
Trace elements
Trace elements
Organic pollutants
-
Other contaminants removed
-
-
No removal
-
-
-
-
-
-
288 - 51.8 (82)
CODi - CODf
(% Removal)
Yes
Yes
Yes
-
Yes
-
Yes
Yes
Yes
Yes
-
-
-
Yes
-
Yes
Yes
Yes
Biochemical
analysis of
biomass
Ge et al. (2018)
Ge et al. (2018)
Yun et al. (2014)
Lawton et al.
(2021)
Kube et al. (2022)
Min et al. (2019)
Piotrowski et al.
(2020)
Lawton et al.
(2021)
Neveux et al.
(2016)
Cole et al. (2016)
Ellison et al.
(2014)
Kim et al. (2018)
Roberts et al.
(2013)
Roberts et al.
(2015)
Saunders et al.
(2012)
Cole et al. (2015)
Ali Kubar et al.
(2022)
Cole et al. (2014)
Reference
Table 2 Studies using filamentous algae to treat wastewater, where: DW, dry weight; AFDW, ash free dry weight; TN, total nitrogen; TP, total phosphorus; COD, chemical oxygen demand;
DRP, dissolved reactive phosphorus; DIN, dissolved inorganic nitrogen; DIC, dissolved inorganic carbon and N
H4-N, nitrogen as ammonium
1992
Journal of Applied Phycology (2024) 36:1987–2004
Oedogonium
Oedogonium
Hydrodiction,
Oedogonium,
Anabaena,
Spirulina
Stigeoclonium
Stigeoclonium,
Oedogonium
Oedogonium,
Stigeoclonium,
Hyalotheca
Oedogonium
Municipal
Municipal
Piggery effluent
Synthetic growth
medium
Textile industry
effluent
Water treatment
residuals
Oedogonium,
macrophytes
Oedogonium
Spirogyra
Municipal
Piggery effluent
Slaughterhouse
effluent
Synthetic growth
medium
Genera
Wastewater
Table 2 (continued)
-
10.3 to 13.6 g
m−2 day−1
-
-
-
149 - 37.3 (75)
5.9 - 0.5 (92)
DRP
-
6.2 - 0.4 (93)
65.5 - 2.6 (96)
486 - 73 (85)
61 - 3 (96)
NH4-N
-
6.7 - 1.7 (75)
-
0.65 g N.m-2.d-1
41.2 - 15.7 (62)
0.63 - 0.2 (69)
TPi - TPf
(% Removal)
16.06 - 7.2 (55)
TNi - TNf
(% Removal)
1.13 g m−2 day−1 -
1 to 11 g m
−2
day−1
0.45 g L-1 day-1
0.11 to 0.40 g
m−2 day−1
12.7 to 13.8 g
m−2 day−1
6.8 to 9.9 g m−2
day−1
-
Productivity
(DW)
-
1,140 - 6.4 (99)
-
-
1,474 - 310 (79)
-
90.7 - 34 (63)
53 - 22.8 (57)
-
-
CODi - CODf
(% Removal)
74 % Al
Trace elements
-
-
-
-
Trace elements
-
-
Other contaminants removed
Not assessed
Not assessed
-
-
Not assessed
Not assessed
-
Yes
Not assessed
-
Pathogen
removal
-
-
-
-
Yes
-
Yes
Yes
Yes
Biochemical
analysis of
biomass
Tabinda et al.
(2019)
Roberts et al.
(2018)
Liu et al. (2023)
Valero-Rodriguez
et al. (2020)
Tan et al. (2018)
Rearte et al. (2021)
Neveux et al.
(2016)
Neveux et al.
(2016)
Wang et al (2013)
Ge et al. (2018)
Reference
Journal of Applied Phycology (2024) 36:1987–2004
1993
1994
(A)
120
Initial concentration (mg.L-1)
Fig. 1 Concentration of
chemical oxygen demand ( ),
total phosphorus ( ) and total
nitrogen ( ) in effluents used for
the evaluation of the wastewater treatment performance
of filamentous algae, a) those
using municipal WW, the x-axis
shows the reference of each
study; (b) those conducted with
industrial WW, the x-axis shows
the wastewater type
Journal of Applied Phycology (2024) 36:1987–2004
100
80
60
40
20
0
Reference
(B)
Initial concentration (mg.L-1)
1600
1400
1200
1000
800
600
400
200
0
Wastewater type
with the most reported productivities, but also the one with
the highest variability in productivity. This is understandable
given that this genus has been tested with wastewater from
different sources, at varied water exchange rates, and in a
significant range of PBRs, from 1 L indoor flasks to 27,000
L outdoor tanks and over a broad range of light intensities as
can be observed on Table 3. It is also a cosmopolitan genus
with a high number of reported species, which grow in different environments and has a variety of life habits (Lawton
et al. 2014).
Specifically, in the algal WWT field the relevance of the
productivity lies in its relationship with carbon, nitrogen
and phosphorus removal (Rearte et al. 2021), however, it
cannot be used as a performance indicator in isolation. The
effectiveness of the nutrient uptake and pollutant sequestration is not always directly proportional to the biomass
growth. For example, Neveux et al., (2016) reported 62 %
of TN and 75 % of TP removal on municipal WW using
Oedogonium cultures with productivities ranging from
6.8 to 9.9 g m
−2 day−1 (Neveux et al. 2016). In contrast,
Cole et al., (2016) reported 36.1 % of TN and 64.6 % of
Journal of Applied Phycology (2024) 36:1987–2004
Number of studies
2
1
0
Wastewater type
Fig. 2 Filamentous algae wastewater treatment studies sparging C
O2
enriched air and the CO2 source, the y-axis shows the number of studies performed with each WW, the x-axis the type of WW. Studies performed using purified C
O2 sparging ( ) and studies performed using
CO2 from flue gases ( )
Fig. 3 Genera included in wastewater treatment research; the number
of studies (>1) incorporating a specific genus are indicated in parentheses
TP removal from another municipal WW using the same
genus, while reporting higher biomass yields of between
8.9 and 15.8 g m−2 day−1 . Perhaps, more surprising was
that (Neveux et al. 2016) had less pre-treatment and almost
one order of magnitude higher nutrient concentration than
reported by Cole et al. (2016).
There was a wide range of results regarding the removal
of nitrogen, which was reported only by 17 of the 28
reviewed studies. In seven cases the authors reported
removals equal or greater than 90 % (Wang et al. 2013;
Cole et al. 2015; Ge et al. 2018;
1995
Lawton et al. 2021; Rearte et al. 2021; Ali Kubar et al.
2022) and the lowest nitrogen removal (36.1 %) was
reported for an Oedogonium culture treating municipal
WW (Cole et al. 2016). Phosphorus removal was only
reported by half of the studies. In five cases the removal
was 90 % or higher (Wang et al. 2013; Ge et al. 2018;
Rearte et al. 2021; Ali Kubar et al. 2022; Kube et al.
2022), and the lowest removal (15.7 %) was reported for an
Oedogonium culture growing in synthetic medium without CO2 injection (Cole et al. 2014). Finally, the chemical
oxygen demand removal was reported only by one quarter
of the studies (Wang et al. 2013; Neveux et al. 2016; Ge
et al. 2018; Kim et al. 2018; Tan et al. 2018; Tabinda
et al. 2019; Ali Kubar et al. 2022; Kube et al. 2022), with
results ranging from 99–98 % of removal (Tabinda et al.
2019; Kube et al. 2022) to no detectable removal reported
for a Spirogyra culture growing in municipal effluent (Ge
et al. 2018) or amended contaminated rural stream water
(Kim et al. 2018).
One of the perceived advantages of filamentous algal cultures versus unicellular algal cultures is the ease of separating the biomass from the media once the treatment is completed. Considering biomass separation, 11 studies reported
the biomass was separated from the treated effluent by filtration or retention of the biomass with mesh screens (Cole
et al. 2014, 2015, 2016; Neveux et al. 2016; Min et al. 2019;
Lawton et al. 2021; Rearte et al. 2021; Kube et al. 2022). The
pore or mesh sizes ranged from 85 µm (Kube et al. 2022) to
750 µm (Cole et al. 2014, 2015), most separated Oedogonium cultures. An interesting adaptation was reported (Cole
et al. 2016) where, to prevent the mesh screens from getting
clogged, a tube for air sparging was installed just below the
outlet preventing the accumulation of biomass. Surprisingly,
the remaining studies did not report on how to remove the
algae from the treated wastewater. This is a crucial aspect
that requires more consideration for the future transferability
of the technology to the industry.
Seven studies used filamentous algae alone or combined
with submerged plants to treat effluents with organic or metal
contamination. Four of those studies reported a reduction of
trace element concentrations in ash water from the washing
of flue gases from a coal power plant in Australia (Saunders
et al. 2012; Roberts et al. 2013, 2015; Ellison et al. 2014).
In these studies, the remediation was performed mostly by
Oedogonium cultures, and also Hydrodiction and Rhizoclonium (Saunders et al. 2012). Two other studies reported
metal removal from effluents from a textile industry using
a combination of macrophytes and Oedogonium (Tabinda
et al. 2019) and within a water treatment pond carried out by
Oedogonium (Roberts et al. 2018). Ali Kubar et al. (2022)
also reported acrylonitrile butadiene styrene removal from
an industrial WW using Tribonema cultures. Surprisingly,
three cases (Yun et al. 2014; Neveux et al. 2016; Piotrowski
1996
45
Biomass productivity g.m-2.d-1
Fig. 4 Reported ranges of productivity. The study references
are shown on the x-axis, and the
productivity values (g DW m
-2
-1
day ) on the y-axis. Bars filling
indicate the genera used in the
studies as follows: Hyalotheca
(■), Hydrodiction ( ), Klebsormidium ( ), Oedogonium (
), Spirogyra ( ) and Stigeoclonium ( )
Journal of Applied Phycology (2024) 36:1987–2004
40
35
30
25
20
15
10
5
0
Reference
et al. 2020) reported no data regarding nutrient or metal
removal on effluents with organic load.
Interestingly, 16 out of 28 studies performed analysis
of the biochemical composition of the recovered algal biomass. The proposed application for the produced biomass
was mostly as biofuel feedstock (Cole et al. 2014; Yun et al.
2014; Neveux et al. 2016; Ge et al. 2018; Lawton et al. 2021;
Rearte et al. 2021; Ali Kubar et al. 2022), bioethanol in the
cases where carbohydrates were predominant and biodiesel
when the fatty acids composed the biomass main energy
reserve. There were alternative uses such as livestock feed,
fertilizers and cellulose extraction.
Increasingly, treated wastewater is reused for agricultural
irrigation (Guardiola-Claramonte et al. 2012). From a public
health perspective, the pathogen load of the treated effluent is a key aspect in reducing human exposure to harmful microorganisms, one that was surprisingly overlooked
in most studies. Only one study out of 13 using municipal
WW measured reduction of the faecal indicator Escherichia
coli (Neveux et al. 2016), where Oedogonium ponds treating
municipal WW achieved a 3 log reduction during a summer
study.
Environmental conditions
The main advantage of using algal ponds to treat effluents
comes from the ability of these organisms to utilise solar
energy via photosynthesis to grow and absorb carbon, nitrogen, phosphorus and produce dissolved oxygen for heterotrophic respiration of organic carbon. The main energetic
input of these systems is photosynthetically active radiation
(PAR; 400-700 nm). This variable is key, both for the performance comparison of different cultures and as a design
variable, given that it reflects the energy availability for a
treatment system. To allow a simple review of the different
reported conditions we calculated the average daily photon flux from maximum and lower values of PAR radiation
reported by the studies (Table 3).
Of 28 studies considered in this review, one indoor (Ali
Kubar et al. 2022) and five outdoor (Roberts et al. 2015,
2018; Kim et al. 2018; Tabinda et al. 2019; Piotrowski et al.
2020) experiments do not have PAR received by the cultures reported, thus the remaining 22 studies were compared
(Fig. 5) by the PAR received. All the outdoor cultures in the
reviewed studies shown in Fig. 5 took place in Townsville,
Australia Latitude S 19.26° (Roberts et al. 2013; Cole et al.
2014, 2015, 2016; Neveux et al. 2016). In comparison, the
greenhouse cultures (i.e. receiving sunlight) were carried
out in Ansan, South Korea Latitude N 37.32° (Min et al.
2019); Te Puke, New Zealand Latitude S 37.78° (Lawton
et al. 2021) and Rotorua, New Zealand Latitude S 38.14°
(Lawton et al. 2021). Surprisingly, the indoor experiment
conducted by Yun et al. (2014) was the one to report the
highest photon flux with 65.7 mol photons m-2 day-1. The
experiments performed outdoors or in greenhouses had average PAR radiation values 10-fold higher than those conducted indoors (Fig. 5). Also six of the indoor studies (Saunders et al. 2012; Wang et al. 2013; Ellison et al. 2014; Tan
et al. 2018; Valero-Rodriguez et al. 2020; Liu et al. 2023)
received an average photon flux of 5 mol photons m-2 day-1
or less, which is arguably low.
However, this is only one aspect of the radiation phenomenon. The light attenuation effect of algal biomass, the
geometry and depth of the PBRs play a crucial role in the
effective light distribution through the water column. Rearte
et al. (2021) reported 68.5 μmol photons m
−2 s−1 of average
irradiance inside 6 cm diameter columnar PBRs when the
average incident irradiance was 300 μmol photons m−2 s−1.
In contrast, Min et al. (2019), reported a mean irradiance
of 49.3 μmol photons m
−2 s−1 inside a 30 cm deep raceway
Journal of Applied Phycology (2024) 36:1987–2004
pond receiving a mean incident irradiance of 633 μmol photons m−2 s−1. Unfortunately, most studies lack this information, which would allow for a comparison of the irradiation
received per unit of treating volume.
A unique study conducted by Min et al. (2019) at
Konkuk University, South Korea used a raceway pond with
submerged lighting. The experiment compared the performance of a filamentous green algae culture illuminated
with solar radiation alone versus one sunlight irradiated
culture supplemented with artificial light from LED lamps.
Although the treatment effect increased more than 3-fold
with the underwater light system, it should be noted that
the initial concentrations of TN and TP were low at the
HRAP’s inlet (less than 10 and 1 mg L
-1 respectively);
the effluent was autoclaved to eliminate bacterial activity and the raceway was constructed inside a greenhouse.
Hence, to achieve the enhanced performance, covered
algal ponds with underwater lighting must be constructed
after conventional WWTPs. This might be an interesting
solution for urban situations where the surface availability
is a constraint, allowing larger volumes of treatment per
square metre. However, the CAPEX of a potential WWTP
with this technology is likely higher, which may not be an
accessible solution to WW treatment in small rural and
regional communities.
The size of the cultures is another key aspect of the experimental design given that, generally, larger volumes tend to
reflect more the intricate and complex interactions occurring
within the cultures. The same features that make these mixes
of phototrophic organisms, aerobic bacteria, micro arthropods, and other organisms difficult to model (Rossi et al.
2020) may also make them resilient to environmental fluctuations. Liu et al. (2020) present a scheme which explores
the intricate interactions between the heterogeneous groups
that take part in these systems. The larger volume, which
gives cultures potential buffering capacity for environmental
variations has the drawback that it is often harder to perform
experiments, both because of the research resources and the
logistics.
Figure 6(A) and (B) show the distribution of size and
duration of studies included in this review. As might be
expected, most of the studies were performed with smaller
pond sizes (≤ 100L). More than half of the studies were carried out with culture volumes smaller than 10 L (Saunders
et al. 2012; Wang et al. 2013; Ellison et al. 2014; Yun et al.
2014; Ge et al. 2018; Tan et al. 2018; Tabinda et al. 2019;
Valero-Rodriguez et al. 2020; Lawton et al. 2021; Rearte
et al. 2021; Ali Kubar et al. 2022; Kube et al. 2022; Liu
et al. 2023). Apart from the experiment above by Min et al.,
(2019), there were two studies performed in greenhouses
with 4 L cultures (Lawton et al. 2021). The biggest variability in culture volumes was identified in studies with outdoor
1997
cultures, where the smallest had only 8 L (Tabinda et al.
2019) and the largest 27,000 L (Cole et al. 2016).
Regarding the experimental time frames, half of the
studies had a duration of up to 14 days. Only 10 out of 28
experiments had a duration of more than four weeks. The
remarkable exceptions were a study conducted in Townsville, Australia (Cole et al. 2016), where the researchers
evaluated the performance of the system for one year, and a
study performed in Ansan, South Korea (Kim et al. 2018),
which lasted 210 days. The treatment performance of a short
duration algal culture in WW might not reflect a process that
these systems are able to sustain over long periods. Natural
evolution gave the algae strategies to survive difficult and
changing environments, endure drought periods and flooding
with the related variations in conductivity, nutrient levels,
pH and radiation (Evans, 1959). Studies measuring the algal
performance for short time periods risk having results that
are explained more by a survival state of these organisms
rather than a metabolic process sustainable in time. Imbalanced availability of nitrogen, phosphorus, carbon or lack
of micronutrients can be overcome over time but might be
the cause of sudden or progressive algal growth decline in
longer experiments (e.g. months). Some experiments had
results that do not clearly show whether the cultures reached
a stable point, and in certain cases the productivity even
seemed to have decreasing trends (Roberts et al. 2013).
Also, longer duration studies better describe the treatment performance under changing seasonal conditions. To
design reliable systems delivering treatment year-round, the
effect of the light cycle and temperature variation must be
assessed at some point of the project, especially in non-tropical regions where the winter sunlight can be less than half
of that received in summer. There is a lack of studies exploring the shorter daylight seasons, only 5 were performed in
autumn weeks and 2 across winter weeks. Only in 2 of those
cases was the algal treatment process assessed in non-tropical sites. It is evident that there is a need to explore the
performance of filamentous algal systems, not only across
the seasons but also in regions where the climatic conditions
are more variable during the year. It is recommended that the
final WWTP design and validation are conducted during the
local winter, which is normally the worst-case scenario for
the performance of natural treatment systems.
There is little evidence of an increase in culture size (volume) over the 13 years that this review encompasses (Fig. 7),
suggesting few small-scale systems (≤ 100 L) translated to
larger applications and that there was not an increase in
experiments using large systems. There are some exceptions
though, assuming publication occurred not long after the
experiments were performed, some scale up of experiments
can be identified from 2012 to 2015 and in 2016. In 2015 to
2016, a series of studies were conducted aiming to treat ash
water from a coal fired power plant (Saunders et al. 2012;
Townsville, Australia
Townsville, Australia
Townsville, Australia
Tarong, Australia
Site
Ansan, South
Korea
Te Puke, New
Zealand
Municipal
Piggery effluent
Municipal
Municipal
Municipal
Municipal
Municipal
Municipal
Municipal
Municipal
Municipal
Townsville, Australia
Townsville, Australia
Rotorua, New
Zealand
Townsville, Australia
Townsville, Australia
Municipal
Municipal
Madison, USA
Municipal
Ash water
Contaminated rural Ansan, South
streams
Korea
Ash water
Ash water
ABS industry
effluent
Aquaculture effluent
Aquaculture effluent
Ash water
Wastewater
18.5
Spring (19.33 S)
-
Winter (19.33 S)
Summer (19.33 S)
Summer (37.79 S)
Summer-AutumnWinter-Spring
(19.33 S)
nr (37.32 N)
Summer (19.33 S)
Spring-SummerAutumn (37.32
N)
Summer-Autumn
(43.11 N)
Summer (38.14 S)
2
25.1
15.6
65.7
8.45
5.8
5.8
48.1
16.9
27,000
20
Indoor
Outdoor
Indoor
Indoor
Indoor
Indoor
Indoor
Outdoor
1
10,000
0.35
5
0.8
4
4
20
Greenhouse 4
Greenhouse 8,000
Outdoor
32.3
27.35
Outdoor
48.1
Greenhouse 4
18.8
495
1
6,000
15,000
1
60
864
853
0.9
Culture
volume
(L)
Outdoor
Indoor
Outdoor
Outdoor
Indoor
Outdoor
Outdoor
Outdoor
Indoor
Setting
nr
4.3
nr
nr
3.8
49.3
Spring (19.33 S)
Spring (19.33 S)
-
23.2
nr
Autumn (19.33 S)
-
Local Season (Lati- Photon flux
tude in degrees)
mean (mol
photons m-2
day-1)
Erlenmeyer flasks
Aerated tanks
Erlenmeyer flasks
Shallow trays
Columns
Aquariums
Aquariums
Buckets
Buckets
Raceway pond
Aerated tanks
Buckets
Buckets
Aerated tanks
Glass bottle
Shallow channel
Aerated tanks
Glass bottle
Aerated tanks
Aerated tanks
Aerated tanks
Cube
PBR type
-
-
0,5
50 - 2
14
14
20 - 5
Batch
-
Semicontinuous 20
Semicontinuous
Semicontinuous
Batch
Semicontinuous
Semicontinuous
Semicontinuous
Semicontinuous 4
Semicontinuous 8
Semicontinuous 1
Semicontinuous 20 - 5
Semicontinuous 4
Batch
Semicontinuous nr
Semicontinuous 4
Semicontinuous nr
Semicontinuous nr
Semicontinuous nr
Semicontinuous 1
Semicontinuous 10 - 0.2
Batch
1
8
4.3
2
2
6
6
2
1.7
4.6
52
2
1.7
1.3
3
30
7
2.1
4
1
0.6
1.3
Wang et al (2013)
Neveux et al. (2016)
Kube et al. (2022)
Yun et al. (2014)
Ge et al. (2018)
Ge et al. (2018)
Ge et al. (2018)
Neveux et al. (2016)
Lawton et al. (2021)
Min et al. (2019)
Cole et al. (2016)
Neveux et al. (2016)
Piotrowski et al.
(2020)
Lawton et al. (2021)
Roberts et al. (2015)
Saunders et al.
(2012)
Ellison et al. (2014)
Kim et al. (2018)
Roberts et al. (2013)
Cole et al. (2015)
Ali Kubar et al.
(2022)
Cole et al. (2014)
Operation mode HRT (days) Duration Reference
(weeks)
Table 3 Environmental conditions and culture management parameters during the studies, where PBR: photo bioreactors; HRT: hydraulic retention time; nr: not reported
1998
Journal of Applied Phycology (2024) 36:1987–2004
Roberts et al. (2018)
12
Semicontinuous 7
Buckets
20
Outdoor
Tabinda et al. (2019)
1
Batch
8
Outdoor
Summer-Autumn
(19.33 S)
Townsville, Australia
nr
nr (31.52 N)
Lahore, Pakistan
nr
5
-
Indoor
0.5
Rectangular containers
Buckets
Batch
-
3
Valero-Rodriguez
et al. (2020)
Liu et al. (2023)
5
Semicontinuous nr
Glass bottle
1
2.18
-
Indoor
Rearte et al. (2021)
1.4
Semicontinuous 5 - 1.7
Columns
0.8
13.7
-
Slaughterhouse
effluent
Synthetic growth
medium
Synthetic growth
medium
Textile industry
effluent
Water treatment
residuals
Indoor
Tan et al. (2018)
2
Batch
Erlenmeyer flasks
0.1
Indoor
1.8
Piggery effluent
Wastewater
Table 3 (continued)
Site
Local Season (Lati- Photon flux
tude in degrees)
mean (mol
photons m-2
day-1)
Setting
Culture
volume
(L)
PBR type
Operation mode HRT (days) Duration Reference
(weeks)
Journal of Applied Phycology (2024) 36:1987–2004
1999
Roberts et al. 2013, 2015; Ellison et al. 2014). The progression started from 1 L glass bottles indoors to 15,000 L aerated tanks outdoors. In another case in 2016, the researchers started testing culture conditions and performance on
municipal WW in 20 L buckets ( Neveux et al. 2016), progressed to 10,000 L tanks and finally experimented with
27,000 L ponds (Cole et al. 2016). Finally, Cole et al. (2014,
2015) published two studies where biomass production was
assessed coupled with final treatment of fishery effluent.
Although these two studies were conducted using similar
volume ponds, the first (Cole et al. 2014) had more interventions to the influent ( CO2 sparging and nutrient amendment),
the second (Cole et al. 2015) had fewer interventions but a
longer duration.
The operation mode of the cultures is another condition
to consider because it directly impacts the transferability of
these treatment processes to large scale alternatives in reallife scenarios. The operation of the studies reviewed in this
article were classified as batch and semi-continuous. The
batch mode means the inoculum and the wastewater were put
in the PBR at the beginning of the run and the culture can
be monitored during the process, but no other input occurs
until the end of the experiment (Lim & Shin 2013). Alternatively, the semi-continuous mode implies that there is an
input stream of medium and an exchange of medium with
or without the algae. It is referred to as “semi” because the
medium exchange is normally not constant but performed in
pulses during the run, but there are some exemptions. The
goal of the semi-continuous mode is to reach a steady state
of algal growth/nutrient removal by balancing the inlet and
outlet streams.
Three quarters of all the experiments were operated in
semi-continuous mode, which arguably better reflects the
operational mode for utilities treating wastewater than the
batch mode. The different hydraulic retention times tested
on these studies range from 4.8 h to 15 days, which cover a
wide range of scenarios. Only seven out of all the compiled
experiments were operated in batch mode, generally with
the aim of exploring the nutrient removal dynamics of the
cultures.
Another aspect that must be considered is that filamentous algae, as most organisms, must acclimate upon facing
new environmental conditions, even if these can support the
culture’s growth. One acclimation method that proved to
give good results was to progressively exchange the stock
culture media with the target WW (Neveux et al. 2016;
Rearte et al. 2021).
Finally, regarding the types of photo bioreactors, the most
used containers were buckets and aerated tanks. The first
option was used in seven of the reported studies (Neveux
et al. 2016; Roberts et al. 2018; Tabinda et al. 2019; Lawton
et al. 2021), all performed with natural sunlight either in a
glasshouse or outdoors and using volumes between 4 and
2000
70
Photon flux mean (mol photons.m-2d -1)
Fig. 5 Average irradiance
received by wastewater cultures
of filamentous algae. The study
references are shown on the
x-axis and the reported mean
photon flux (PAR) on the y-axis.
Indoor studies ( ), greenhouse
studies ( ) and outdoor studies
( )
Journal of Applied Phycology (2024) 36:1987–2004
60
50
40
30
20
10
0
Reference
(A)
14
Duration (weeks)
12
10
8
6
4
2
0
0
5
10
15
20
25
30
35
40
45
50
55
60
65
Culture volume (L)
(B)
60
50
Duration (weeks)
Fig. 6 Culture volume and
experimental duration, (A)
conducted with cultures ≤100
L, and (B) cultures > 100 L.
Culture volumes (L) are shown
on the x-axis, duration in weeks
is shown on the y-axis. Studies
carried out indoors (×) inside
greenhouses ( ) and outdoors
( )
40
30
20
10
0
0
5000
10000
15000
Culture volume (L)
20000
25000
30000
Journal of Applied Phycology (2024) 36:1987–2004
70
30000
60
25000
50
40
15000
30
> 100 (L)
20000
< 100 (L)
Fig. 7 Experimental culture
volumes for studies reported
2012 -2022. The left y-axis
indicates the volume of the
cultures < 100 L (■), the right
y-axis indicates the volume of
the cultures > 100 L ( ), and
the x-axis indicates the year that
these studies were published
2001
10000
20
5000
10
0
2010
2012
2014
2016
2018
2020
2022
0
2024
Year of publication
20 L. The aerated tanks were used in seven cases in outdoor
settings with culture volumes between 60 and 27000 L (Roberts et al. 2013, 2015; Cole et al. 2014, 2015, 2016; Neveux
et al. 2016; Piotrowski et al. 2020). The rest of the studies
used a variety of laboratory containers, such as Erlenmeyer
flasks, clear acrylic columns, cubic flasks and glass bottles,
or models of raceway ponds.
Discussion
From a phycological point of view, even if this is a niche
within the algal wastewater treatment field, which has seen
publications of experimental studies for only 13 years, there
has been a worthy exploration of many filamentous genera.
Bioprospecting has consistently identified Oedogonium spp.,
Spirogyra spp., Hydrodiction spp. and Stigeoclonium spp. as
suitable candidates for wastewater treatment as they are the
three most used genera in the studies reviewed here.
It is surprising that there are more studies exploring
filamentous algal biomass productivity and its biochemical
quality than analysing the nitrogen or phosphorus removal
from the wastewater. Furthermore, only one study assessed
pathogen removal (Neveux et al. 2016). This suggests
that there is more interest in producing biomass and the
possible derived bio-compounds, than the performance
regarding wastewater treatment to protect public health.
Even if both processes are coupled, the system will not
always promote them equally. Depending on design parameters, the algal strains, wastewater types, retention times
and types of PBRs, algal ponds can be constructed with a
spectrum of goals. We could frame that spectrum between
two approaches. Firstly, using wastewater to produce biomass, where the effluent is just regarded as a free source
of nutrients for algal growth. In this case the wastewater
treatment is a secondary effect that adds attractiveness to
the system given its environmental benefit. Interrogating the reported productivities in the reviewed literature
it becomes apparent that there is a likely bottleneck for
the biomass production approach. If a system can sustain
a productivity of 20 g m -2 d ay-1, which only four studies in this review attained (Roberts et al. 2013; Cole et al.
2014, 2015; Kim et al. 2018), a 1 ha pond would produce
200 kg of dry biomass per day. This implies a limitation
on the possible economical exploitation, using a biorefinery approach, able to access only 73 t of raw material
per year. Secondly, treating wastewater with algal ponds,
where the main goal is to improve the effluent quality for
discharge, and the generated biomass is regarded just as
a by-product together with treated wastewater for reuse.
Taking these aspects into consideration, the utilisation of
filamentous algae may be more readily adopted to satisfy
an environmental need for wastewater treatment, producing
an increasingly valuable product of treated wastewater. A
commodity that is expected to be progressively scarcer in
some regions due to climate change.
Having considered most of the factors playing a role in
filamentous algal bioreactors performance, attempting to
find relationships is desirable. Figure 8 (A) shows the studies, which reported biomass areal productivity, the wastewater
initial nitrogen concentration and nitrogen removal. The first
observation is that there is a lack of information meeting the
requirements for this kind of comparison. There are too few
data points to elaborate conclusions about different genera’s
2002
(A)
45
40
Total Nitrogen (mg.L-1)
Fig. 8 Reported biomass
productivity compared to (A)
wastewater total nitrogen concentration before the algal pond
(▲) and after the treatment (●).
The y-axis indicates the TN
concentration, and the x-axis
indicates the biomass productivity. (B) Biomass productivity
compared to hydraulic retention
time ( ) and photon flux (■),
the right y-axis indicates the
hydraulic retention time, the left
y-axis indicates the photon flux
and the x-axis indicates the biomass productivity. On both (A)
and (B) the marker’s colours
indicate the genus of the algae
Spirogyra ( ), Hydrodiction ( )
and Oedogonium ( )
Journal of Applied Phycology (2024) 36:1987–2004
35
30
25
20
15
10
5
0
0
5
10
15
20
25
30
35
40
45
Productivity (g DW .m .d )
(B)
60
50
20
40
15
30
10
20
5
10
Photon flux mean (mol photons.m-2.d-1)
Hydraulic retention time (days)
25
0
0
0
5
10
15
20
25
30
35
40
45
Productivity (g DW .m .d )
performances, for example. However, it is possible to conclude the data does not show a correlation between the initial
total nitrogen concentration of the influent and the biomass
productivity, nor with nitrogen removal. A way of making
sense of this data is looking at the HRT and photon flux (Fig 8
(B)), which also shows a lack of information to assess correlations. In spite of this, an incipient effect can be deduced from
the variation in HRT, the shorter the retention time, the higher
the productivity. A logical phenomenon given that accelerating the pond’s medium exchange implies higher nutrient
fluxes. Finally, the photon flux received by the ponds seems
to have a share in the phenomenon, understandably, as this is
the energy input of the algal-bacterial consortia.
Each case study has different wastewater types and scenarios.
As can be noticed in the literature, researchers across the world
have attempted to use filamentous algal ponds to improve the
wastewater quality in diverse settings and address the industries
or populations needs. A thoughtful analysis of the projects must
consider the origin of the influents and the treatment goals of
the algal systems. There is great potential for filamentous algal
ponds treating secondary effluent, replacing the aerobic stage
or more steps of the conventional treatment process, for a simple solar powered system that does not rely on consumables or
long retention times. This is an area within the field that is still
in the first steps, with the capacity of addressing the needs of
small communities especially in rural areas for easy to operate
WWTPs and the bonus of in situ water recycling.
In other cases, there is an interest in further improving
the quality of tertiary or fully treated effluents, particularly
before discharge into water bodies. Even when the N-P-C
levels are considerably low, large volumes constantly discharged into rivers, freshwater lakes or marine bays can have
a dramatic ecological impact over time, also deteriorating
Journal of Applied Phycology (2024) 36:1987–2004
strategic economical resources. It can also be the case that an
existing treatment scheme needs improvement or expand it’s
capacity due to population or industry growth. This would
be a different opportunity for filamentous algal ponds to
provide an accessible solution at a lower cost compared to
other systems, particularly at sites where land occupation is
not an issue.
Organic pollutants and heavy metals removal is a goal
addressed by a minority of the published studies, and one
where it is even more difficult to reach general conclusions
given that the trade-off between employed resources and
achieved goals changes from one scenario to the other.
Conclusion
The primary benefit of filamentous algae is most likely
wastewater treatment, enabling nutrient removal and importantly improved low cost biosolids separation when compared to microalgal systems. The most used filamentous alga
was Oedogonium. The review highlighted the importance
of reporting the composition of the influent and treated
wastewater to enable assessment of treatment performance.
Increasing wastewater reuse also requires the composition
analysis and performance include microbiological parameters of public health significance. Supplementing wastewater
with nutrients and CO2 or diluting influents to enable filamentous algal growth should be avoided since it is unlikely
to be a practical or economic option acceptable to water
utilities for large scale wastewater treatment. Many of the
studies reviewed emphasised filamentous algal productivity
and composition. Although the biomass produced may be
considered a secondary benefit, filamentous algal productivity data suggests large scale wastewater treatment systems
will be required to produce sufficient biomass for economic
viability. The review clearly demonstrates that, except for
the research at James Cook University, Australia, few studies
have transitioned from laboratory to field scale application.
To further the adoption of the technology it is recommended
future research focus on the acclimation of filamentous algae
to growth in wastewater, which has received as minimum
prior intervention as possible, with the objective of rapidly
transitioning from laboratory to outdoor experimentation at
scale.
Supplementary Information The online version contains supplementary material available at https://d oi.o rg/1 0.1 007/s 10811-0 24-0 3220-2.
Author contribution All authors contributed to the study conception
and design. Material preparation, data collection and analysis were
performed by Felipe Sabatte, Ryan Baring and Howard Fallowfield.
The first draft of the manuscript was written by Felipe Sabatte and all
authors commented on previous versions of the manuscript. All authors
read and approved the final manuscript.
2003
Funding information Open Access funding enabled and organized by
CAUL and its Member Institutions. The authors did not receive support
from any organization for the submitted work.
Data availability The data upon which this review was written was
obtained from the referenced articles and collated in a table available
in the supplementary material. The corresponding author agrees to be
contacted if consultation is needed.
Declarations
Competing interests The authors have no competing interests to
declare that are relevant to the content of this article.
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long
as you give appropriate credit to the original author(s) and the source,
provide a link to the Creative Commons licence, and indicate if changes
were made. The images or other third party material in this article are
included in the article’s Creative Commons licence, unless indicated
otherwise in a credit line to the material. If material is not included in
the article’s Creative Commons licence and your intended use is not
permitted by statutory regulation or exceeds the permitted use, you will
need to obtain permission directly from the copyright holder. To view a
copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
References
Acién FG, Gómez-Serrano C, Morales-Amaral MM, Fernández-Sevilla
JM, Molina-Grima E (2016) Wastewater treatment using microalgae: how realistic a contribution might it be to significant urban
wastewater treatment? Appl Microbiol Biotechnol 100:9013–9022
Ali Kubar A, Jin N, Cui Y, Hu X, Qian J, Zan X, Zhang C, Zhu F,
Kumar S, Huo S (2022) Magnetic/electric field intervention on
oil-rich filamentous algae production in the application of acrylonitrile butadiene styrene based wastewater treatment. Bioresour
Technol 356:127272
Blersch DM, Kangas PC, Mulbry WW (2013) Turbulence and nutrient
interactions that control benthic algal production in an engineered
cultivation raceway. Algal Res 2:107–112
Chu R, Li S, Zhu L, Yin Z, Hu D, Liu C, Mo F (2021) A review on
co-cultivation of microalgae with filamentous fungi: Efficient
harvesting, wastewater treatment and biofuel production. Renew
Sustain Energy Rev 139:110689
Cole AJ, de Nys R, Paul NA (2015) Biorecovery of nutrient waste as
protein in freshwater macroalgae. Algal Res 7:58–65
Cole AJ, Neveux N, Whelan A, Morton J, Vis M, de Nys R, Paul NA
(2016) Adding value to the treatment of municipal wastewater
through the intensive production of freshwater macroalgae. Algal
Res 20:100–109
Cole AJ, De Nys R, Paul NA (2014) Removing constraints on the biomass production of freshwater macroalgae by manipulating water
exchange to manage nutrient flux. PLoS ONE 9:
Ellison MB, De Nys R, Paul NA, Roberts DA (2014) Growth and metal
bioconcentration by conspecific freshwater macroalgae cultured
in industrial waste water. PeerJ 22:e401
Evans JH (1959) The survival of freshwater algae during dry periods:
Part II. Drying experiments: Part III. Stratification of algae in
pond margin litter and mud. J Ecol 47:55–81
Fallowfield HJ, Young P, Taylor MJ, Buchanan N, Cromar N, Keegan
A, Monis P (2018) Independent validation and regulatory
2004
agency approval for high rate algal ponds to treat wastewater from rural communities. Environ Sci: Water Res Technol
4:195–205
Ge S, Madill M, Champagne P (2018) Use of freshwater macroalgae Spirogyra sp. for the treatment of municipal wastewaters and
biomass production for biofuel applications. Biomass Bioenergy
111:213–223
Guardiola-Claramonte M, Sato T, Choukr-Allah R, Qadir M (2012)
Wastewater production, treatment and reuse around the Mediterranean region: Current status and main drivers. In: ChoukrAllah R, Ragab R, Rodriguez-Clemente R (eds) Integrated Water
Resources Management in the Mediterranean Region. Springer,
Dordrecht, pp 139–174
Kim T, Ren X, Chae KJ (2018) High-rate algal pond coupled with a
matrix of Spirogyra sp. for treatment of rural streams with nutrient
pollution. Environ Manag 213:297–308
Kube M, Fan L, Roddick F, Whitton R, Pidou M, Jefferson B (2022)
High rate algal systems for treating wastewater: A comparison.
Algal Res 65
Lawton RJ, Cole AJ, Roberts DA, Paul NA, de Nys R (2017) The
industrial ecology of freshwater macroalgae for biomass applications. Algal Res 24:486–491
Lawton RJ, Glasson CRK, Novis PM, Sutherland JE, Magnusson ME
(2021) Productivity and municipal wastewater nutrient bioremediation performance of new filamentous green macroalgal cultivars. J Appl Phycol 33:4137–4148
Lawton RJ, De Nys R, Skinner S, Paul NA (2014) Isolation and identification of Oedogonium species and strains for biomass applications. PLoS ONE 9:e90223
Lim HC, Shin HS (2013) Fed-batch cultures : principles and applications of semi-batch bioreactors. Cambridge University Press,
Cambridge
Liu J, Pemberton B, Lewis J, Scales PJ, Martin GJO (2020) Wastewater
treatment using filamentous algae – A review. Bioresour Technol
298:122556
Liu J, Pemberton B, Scales PJ, Martin GJO (2023) Ammonia tolerance of filamentous algae Oedogonium, Spirogyra, Tribonema
and Cladophora, and its implications on wastewater treatment
processes. Algal Res 72:103126
Min KJ, Lee J, Park KY (2019) Advanced wastewater treatment using
filamentous algae in raceway ponds with underwater light. Energy
Sources Part A: Recov Util Environ Effects 41:1674–1682
Mulbry W, Kangas P, Kondrad S (2010) Toward scrubbing the bay:
Nutrient removal using small algal turf scrubbers on Chesapeake
Bay tributaries. Ecol Eng 36:536–541
Neveux N, Magnusson M, Mata L, Whelan A, de Nys R, Paul NA
(2016) The treatment of municipal wastewater by the macroalga
Oedogonium sp. and its potential for the production of biocrude.
Algal Res 13:284–292
Park JBK, Meerman C, Craggs R (2019) Continuous low dosing of
cationic polyacrylamide (PAM) to enhance algal harvest from a
hectare-scale wastewater treatment high rate algal pond. N Z J
Bot 57:112–124
Piotrowski MJ, Graham LE, Graham JM (2020) Temperate-zone cultivation of Oedogonium in municipal wastewater effluent to produce
cellulose and oxygen. J Ind Microbiol 47:251–262
Journal of Applied Phycology (2024) 36:1987–2004
Rearte TA, Rodriguez N, Sabatté F, Fabrizio de Iorio A (2021) Unicellular microalgae vs. filamentous algae for wastewater treatment
and nutrient recovery. Algal Res 59:102442
Roberts DA, Paul NA, Bird MI, de Nys R (2015) Bioremediation
for coal-fired power stations using macroalgae. Environ Manag
153:25–32
Roberts DA, De Nys R, Paul NA (2013) The effect of CO2 on algal
growth in industrial waste water for bioenergy and bioremediation
applications. PLoS ONE 8:e81631
Roberts DA, Shiels L, Tickle J, De Nys R, Paul NA (2018) Bioremediation of aluminium from the wastewater of a conventional water
treatment plant using the freshwater macroalga Oedogonium.
Water 10:626
Rossi S, Casagli F, Mantovani M, Mezzanotte V, Ficara E (2020) Selection of photosynthesis and respiration models to assess the effect
of environmental conditions on mixed microalgae consortia grown
on wastewater. Bioresour Technol 305:122995
Saunders RJ, Paul NA, Hu Y, de Nys R (2012) Sustainable sources
of biomass for bioremediation of heavy metals in waste water
derived from coal-fired power generation. PLoS ONE 7:e36470
Tabinda AB, Arif RA, Yasar A, Baqir M, Rasheed R, Mahmood A,
Iqbal A (2019) Treatment of textile effluents with Pistia stratiotes,
Eichhornia crassipes and Oedogonium sp. Int J Phytoremediation
21:939–943
Tan KA, Morad N, Harlina A, Ong SL (2018) Removal of COD, BOD
and nutrients in swine manure wastewater using freshwater green
microalgae. Malays J Microbiol 14:187–194
Valero-Rodriguez JM, Swearer SE, Dempster T, de Nys R, Cole AJ
(2020) Evaluating the performance of freshwater macroalgae in
the bioremediation of nutrient-enriched water in temperate environments. J Appl Phycol 32:641–652
Wang H, Hu Z, Xiao B, Cheng Q, Li F (2013) Ammonium nitrogen
removal in batch cultures treating digested piggery wastewater
with microalgae Oedogonium sp. Water Sci 68:269–275
Young P, Taylor M, Fallowfield HJ (2017) Mini-review: high rate algal
ponds, flexible systems for sustainable wastewater treatment.
World J Microbiol Biotechnol 33:117
Young P, Taylor MJ, Buchanan N, Lewis J, Fallowfield HJ (2019) Case
study on the effect continuous C
O2 enrichment, via biogas scrubbing, has on biomass production and wastewater treatment in a
high rate algal pond. Environ Manage 251:109614
Young P, Phasey J, Wallis I, Vandamme D, Fallowfield H (2021) Autoflocculation of microalgae, via magnesium hydroxide precipitation, in a high rate algal pond treating municipal wastewater in the
South Australian Riverland. Algal Res 59:102418
Yun JH, Smith VH, Denoyelles FJ, Roberts GW, Stagg-Williams SM
(2014) Freshwater macroalgae as a biofuels feedstock: Minireview and assessment of their bioenergy potential. Ind Biotechnol 10:212–220
Publisher's Note Springer Nature remains neutral with regard to
jurisdictional claims in published maps and institutional affiliations.