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Life cycle assessment of the water and wastewater

system in Trondheim, Norway – A case study
a a
Helene Slagstad & Helge Brattebø
a
Department of Hydraulic and Environmental Engineering, Norwegian University of Science
and Technology, 7491, Trondheim, Norway
Published online: 17 Jun 2013.

To cite this article: Helene Slagstad & Helge Brattebø (2014) Life cycle assessment of the water and wastewater system in
Trondheim, Norway – A case study, Urban Water Journal, 11:4, 323-334, DOI: 10.1080/1573062X.2013.795232

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 Urban Water Journal, 2014
Vol. 11, No. 4, 323–334, http://dx.doi.org/10.1080/1573062X.2013.795232

CASE STUDY
Life cycle assessment of the water and wastewater system in Trondheim, Norway – A case study
Helene Slagstad* and Helge Brattebø
Department of Hydraulic and Environmental Engineering, Norwegian University of Science and Technology, 7491, Trondheim, Norway
(Received 19 March 2012; final version received 8 April 2013)

This study presents the results from a life cycle assessment (LCA) performed on the water and wastewater system in the city

of Trondheim. The objective of the study was to examine the system-wide life cycle environmental impact potentials of
operating the city’s water and wastewater system, in order to clarify the relative importance of different environmental
impact categories and how different elements of the water and wastewater system contribute to these impacts. As the results
of this study were used in the planning of a new carbon-neutral urban settlement, the climate change impact was of special
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interest. Freshwater eutrophication due to the consumption of energy and chemicals was found to be the impact category
with the largest contribution to the total environmental impact. In practice, urban water utilities would have to perform a
trade-off between the consumption of energy and chemicals and the discharge of pollutants to receiving waters.
Keywords: carbon neutrality; life cycle assessment; urban water infrastructure

1. Introduction environmental effect of the system. The advantage with

The services provided by urban water and wastewater LCA is that it not only takes direct emissions into account,
utilities are based on legislations on water supply and but also includes impacts resulting from production and
wastewater management, including standards for water transportation of resources, construction and maintenance
quality and pollution discharge to the local receiving water of buildings and infrastructure, end-of-life management,
bodies. Utilities commonly have a strong focus on water etc.
quality, treatment efficiencies and cost-effectiveness; LCA has been used in the water and wastewater
however, during recent years increasing focus is given to research for some time (Lundin et al. 2000, Ortiz et al.
wider sustainability criteria, including carbon dioxide 2007, Remy and Jekel 2008, Stokes and Horvath 2010,
emissions and life cycle environmental impacts. Godskesen et al. 2011, Stokes and Horvath 2011). Yet
Water and wastewater infrastructures play an import­ studies focusing on the entire water and wastewater system
ant role in daily urban life. To perform this role the system are relatively few in number. Among those studies,
consumes materials, chemicals and energy for the Lassaux et al. (2007) examined the water and wastewater
construction, operation and maintenance of treatment system in the Walloon Region in Belgium. They found that
plants, pipeline networks, reservoirs and pumping stations, the environmental impact of the water system was less
all of which are associated with environmental impacts. than the environmental impact of the wastewater system,
There are different methodologies available for estimating and that the most important environmental strains were
the environmental impact of these systems. When derived from water discharge, wastewater treatment
analysing the assessment of recycled water schemes, operations and, to a lesser extent, the sewer system.
Chen et al. (2012) compared the use of Material Flow Venkatesh and Brattebo (2011) developed a ‘metabolism
Analysis (MFA), Life Cycle Assessment (LCA) and model’ for urban water systems, and studied the energy
Environmental Risk Assessment (ERA). They found that consumption, costs and environmental impact of urban
MFA is an effective initial screening method, that LCA is water cycle services in Oslo. Their study demonstrated that
widely used in finding the optimal wastewater treatment the wastewater treatment plants have the highest
technology and that ERA mainly evaluates site-specific environmental impact, most notably from acidification
chemical hazards. Stokes and Horvath (2011) demon­ and eutrophication. After weighting, they found that global
strated how estimating the environmental impact of water warming accounted for only 6% of the total impact score
systems without including the life cycle impact of energy when considering the operation and maintenance phase of
and materials can significantly underestimate the total the system. Lundie et al. (2004) conducted a prospective

*Corresponding author. Email: helene.slagstad@ntnu.no

q 2014 Taylor & Francis
 324 H. Slagstad and H. Brattebø

LCA on the water and wastewater system of Sydney, out processes assumed to be of minor interest in the study
Australia, as a basis to recommend measures for at hand can result in the omission of significant impacts.
improving the system’s environmental performance. Moreover, LCA employs generic characterisation factors
In Trondheim, Norway, a new ‘carbon-neutral’ urban for local or regional impacts, such as eutrophication.
settlement is planned, at Brøset. The average annual As will be discussed in this case study, so long as these
global-warming impact in Norway is 14.9 tonnes of CO2­ characterisation factors are not regionalised, results must
eq per person (Hertwich and Peters 2009). In effort to be interpreted in the light of local conditions. Work is
achieve carbon-neutrality at Brøset, every part of the undertaken to improve the accuracy of regional impact
project, including the water and wastewater system must categories. In addition to these factors we have to deal with
contribute to impact reduction. There has been limited uncertainty in the parameters used in the assessment.
knowledge of the impact of conventional water and The functional unit of our study consist of a one-year
wastewater systems in Norway, and before new alternative provision of water, and collection, transportation and
solutions at Brøset were suggested the conventional treatment of wastewater (including stormwater) for
system in Trondheim had to be thoroughly examined. The Trondheim, Norway. The system boundaries are given in
objective of this study was to quantify the system-wide life Figure 1. The LCA-programme Simapro version 7.3.2 (Pré
cycle environmental impact potentials of operating the Consultants 2011), with the Ecoinvent database was used
city’s water and wastewater system, in order to clarify the for the assessment. Ecoinvent has life cycle inventory data
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relative importance of different environmental impact on energy supply, resource extraction, material supply,
categories and how different elements of the water and chemicals, metals, agriculture, waste management ser­
wastewater system contribute to these impacts. Particular vices, and transport services. These data are combined with
focus is given to the system-wide carbon dioxide data for energy and material use and data for embodied
emissions and contributions to climate change, since this energy calculations for buildings, pipelines, pumps, and
is in general a high priority issue for water utilities, and for water storage devices. Emissions from overflow, effluent
Trondheim in particular due to the planning of the new and sludge, fertiliser substitution, and transportation were
urban settlement with the ambition of carbon-neutral also accounted for. Impact categories dealing with toxicity,
solutions. Possible improvements to the system will be however, were excluded from the study due to lack of data
discussed, but not assessed at this stage. We claim that on toxic elements in effluent, overflow, and sludge. For the
more knowledge and better methods are needed for impact assessment, the midpoint impact assessment
assessing the environmental impact of water and method ReCiPe (midpoint (H) v1.06, July 2011), with
wastewater systems, and this case study helps to expand normalisation values for Europe, was applied. ReCiPe 2008
the knowledge about the environmental impacts of water builds on the Eco-indicator 99 and the CML Handbook on
and wastewater systems in urban areas. LCA, and is an impact assessment method harmonised with
respect to modelling principles and choices concerning
midpoint and endpoint impact assessments (Goedkoop
2. Methodology
et al. 2012). The processes included in the assessment are
2.1. Life cycle assessment given in the Appendix.
In accordance with the literature, we decided that LCA is
the best method for assessing system-wide environmental
impact potentials of the current water and wastewater 2.2. Case system description
system in Trondheim. There are other tools available for Trondheim is the third largest city in Norway, with
assessing environmental impacts of different systems; 171,000 inhabitants. The water is supplied from surface
however, due to its unique and comprehensive life-cycle water collected from a large nearby lake called
perspective, LCA is found superior to other methods, such Jonsvatnet (Figure 2). Water is treated in a central
as Strategic Environmental Assessments, Cost-Benefit water treatment plant at Vikelvdalen (VIVA), then
Analysis, Material Flow Analysis, Environmental Risk distributed for consumption, followed by collection of
Assessment, or Ecological Footprints (Finnveden et al. stormwater and wastewater for treatment in one of the
2009, Chen et al. 2012). Life cycle assessment is city’s two wastewater treatment plants - one at
standardized (ISO 2006a, 2006b), and commercial LCA- Høvringen (HØRA) and one at Ladehammeren
software programmes are mature and robust (Chen et al. (LARA). After treatment the effluent is discharged into
2012). LCA is effective for evaluating the environmental the fjord. Stormwater is either collected in a separate
impacts of the systems under study, but the methodology pipeline system before being directly discharged into the
also has constraints. LCAs can be data intensive and time fjord, or is sent for treatment together with wastewater in
consuming, and deciding what should be included or a combined sewage pipeline network. The system is
excluded in the assessment is therefore important. Hence, described in more detail below. The data collected for
setting the system boundaries can be challenging; leaving the system were from 2010.
 Urban Water Journal 325
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Figure 1. Water and wastewater flow diagram for Trondheim.

Figure 2. The case study area.

 326 H. Slagstad and H. Brattebø

2.2.1. Potable water production and distribution consumers. Therefore, it was assumed that consumers
VIVA treated 22.3 million m3 of water in 2010, a small expelled 13.9 million m3 of wastewater annually.
fraction of which was also supplied to neighbouring
municipalities. The facility used calcite, sodium hypo­
2.2.4. Wastewater
chlorite (which is produced at the plant), carbon dioxide,
and UV-filtration for treating the water to approved quality Of the wastewater pipeline network in the city, 60% of the
standards. This is a simple but efficient water treatment pipes were part of a separate system (sewage and
method suitable for producing good quality surface water. stormwater flowing separately), although 10% of these
The municipality of Trondheim encompasses a surface pipes connected to combined sewers downstream. This,
area of 342 km2, and 3.5 GWh was used for the 22 pumps in effect, means that 50% of the sewage entered the
in the water distribution network. Twelve water storage wastewater treatment plants (WWTPs) through combined
tanks were connected to the system, and all were sewers and 50% through dedicated sewage-carriers. The
accounted for in the calculations. A significant percentage Høvringen wastewater treatment plant (HØRA), with a
of treated water was lost by leakage from the pipeline catchment area of 95 km2, treated 20.6 million m3 of
network, as some of the pipelines were nearly 150 years wastewater in 2010, while the Ladehammeren wastewater
old and the level of maintenance has been low for many treatment plant (LARA), with a catchment area of 18.7
years. In fact, even some of the pipelines installed as late km2, treated 11.1 million m3 of wastewater in 2010. About
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as the 1960s and 1970s were of poor quality - especially 50% of the wastewater was from industrial consumers.
the ductile iron pipes which have not been coated for The wastewater at LARA was more concentrated when
corrosion protection. Water leakages accounted for compared to HØRA, due to a smaller amount of
approximately 32% of the treated water that originated stormwater entering LARA at an almost equal hydraulic
from the treatment plant. In other words, only 13.9 million load measured in Person Equivalents (PE). To find the
m3 of the 20.5 million m3 of potable water produced for amount of stormwater that entered the two plants, some
Trondheim was actually available to the consumers. estimates had to be made because of the lack of available
data on flows between the input to consumers and the input
to the WWTPs. The estimates were based on the volume of
water going to the consumers, the volume of wastewater
2.2.2. Pipelines entering the WWTPs, the PE connected to each plant, and
By calculating the masses of pipes, based on known the approximate distribution of 50% for the separate
lengths, diameters, and materials of construction, a system and 50% for the combined sewers. The complete
detailed study was performed on the embodied energy in system is depicted in Figure 1. The notations refer to the
the 1900 km of pipelines in the public network (as different flows in the system.
distinguished from the private network). Assumptions HØRA is a mechanical treatment plant using polymers
about pipe thickness based on pipe diameter and material for improved sedimentation and dewatering. It had a
used were sourced from Venkatesh (2011). A diesel BOD5 reduction rate of 49.2%, and a tot-P reduction rate
consumption of 29.35 MJ/m was assumed for installation ­ of 25%. X5,10 (inflows to the treatment plant from
the same as that used in the Ecoinvent database for pipe combined sewer pipelines) was estimated to be 17.8
installations. The lifetimes assumed were based on local million m3, and X6,10 (inflows to the treatment plant from
knowledge, with 100 years for concrete, asbestos cement, separate sewage pipelines) was estimated to be 2.8 million
and ductile iron pipes, 70 years for steel and copper pipes, m3. The plant consumed 2.3 GWh of electricity and 0.17
and 120 years for PE, PP, PVC, synthetic fibre, and glass million litres of oil per year, and it produced 0.57 million
fibre pipes. For wastewater pipelines, concrete was by far Nm3 of biogas, which was used internally for heating the
the most dominant material by mass. For water pipelines, sludge. Complete combustion of the biogas with no
it was ductile iron, although concrete was by no means emissions of hydrogen sulphide, carbon monoxide, and
insignificant. Maintenance of the pipes was not included in ammonia was assumed.
the assessment. LARA, on the other hand, is a chemical treatment
plant, with a reduction rate of 45.3% of BOD5 and 80.1%
of tot-P. In this plant, 8.3 million m3 of wastewater entered
2.2.3. Consumers through combined sewers (X8,13), and 2.8 million m3
The use phase of the water was omitted from our analysis. consisted of untreated sewage entering from the separate
This means that private pipes, other in-house installations, system (X7,13). Iron chloride, together with polyamine and
and energy for water heating were excluded from the polymer, was used for sedimentation, and polymer was
calculations. It was assumed that the volume of potable also used for dewatering. The plant used 2.2 GWh of
water entering the system was equal to the volume of electricity and produced 0.8 million Nm3 of biogas.
wastewater discharged by private, public, and industrial Around 60% of the biogas was used internally for heating,
 Urban Water Journal 327

while 40% was used for hot water production, which was tons of sludge produced, 69% was used in agriculture,
delivered to the district heating system in city. Thus, the 30% for greening, and 1% was deposited. Plant
hot water used in the district-heating system avoided the availability of nitrogen and phosphorous were assumed
use of an annual average energy mix consisting of 72.4% to be 50% and 70% respectively (Remy 2010), and the
electricity, 18.5% fuel oil, 5.2% wood, and 3.9% natural fertilizer substituted was assumed to be Super Phosphate
gas. As we can see, electricity (predominantly from and Urea. Therefore, 12,700 kg Super Phosphate and
hydropower) is the main heating source in Norway. 34,900 kg Urea were substituted.
Norway is, however, part of a Nordic electricity market, Two additional flows had to be considered: the flow
and we therefore choose to use a Nordic electricity mix in from the separate stormwater pipelines (X4,18 and X9,18),
the calculations. This choice was tested in the sensitivity and the overflow from the combined sewer pipelines (X5,18
analyses. and X8,18). For the stormwater system, the pipelines and the
There are three main outflows from the WWTPs – pumping energy were taken into consideration; the
effluent, overflow, and sludge. The overflow and the environmental impacts associated with the flow of the
effluent from the WWTPs enter the Trondheim fjord, stormwater into rivers/fjord were not accorded much
which is connected to the Norwegian Sea. The Norwegian importance in this analysis. The overflows, on the other
Sea, as well as the Trondheim fjord, is considered to be hand, occur when the combined sewer system is overloaded
robust in terms of eutrophication; still large WWTPs are because of heavy rain or failures in the system: untreated
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expected, by regulation, to have secondary treatment if sewage then enters rivers. This is a problem since the rivers
special permissions have not been conferred, as in the enter the fjord in shallow waters near popular beaches,
case of Trondheim. The phosphorous concentration in the which tend to get contaminated with bacteria after heavy
inflow and outflow of the plant was known, and therefore rainfall. The municipality has decided on a policy to reduce
it was easy to calculate the phosphorous content of the overflow into the fjord by rehabilitating the existing
effluent, overflow, and sludge. Nitrogen content, on the pipe network, and it is assumed that about 6% of the
other hand, was not measured, and some assumptions had wastewater in combined sewers is presently discharged as
to be made. According to standards used by Statistics overflows annually. Data on the exact concentration of
Norway, the ratio between phosphorous and nitrogen is these overflows was not available; an even distribution of
1.6:12 (SSB 2010). The nitrogen amount in the untreated sewage and stormwater over the year was
wastewater was therefore estimated based on the known therefore assumed. In the HØRA catchment area an
phosphorous content. Treatment efficiencies for mechan­ overflow of 1.1 million m3 (X5,18) was assumed, while the
ical and chemicals plants were taken from Venkatesh and LARA catchment area gave an overflow of 0.5 million m3
Brattebo (2009). While the nitrogen entering the sea has (X8,18). The eutrophication potential takes these overflows
eutrophication potential, nitrous oxide (N2O) is a into account.
greenhouse gas contributing to global warming with a A small wastewater treatment plant treating less than
factor of 298 times greater than CO2 (IPCC 2007). The 1% of the water in town was omitted from the calculations
2006 IPCC Guidelines for National Greenhouse Gas due to a lack of reliable data. Emissions associated with
Inventories estimates the emission factor of N2O to be the spreading of sludge and mineral fertilizer were also
0.5% of the nitrogen content of the effluent (IPCC 2006). excluded, on the assumption that these processes have
The uncertainty is great, however, with a range from negligible environmental impacts.
0.05% to 25%. For the time being these are the best
estimates available. Still it must be borne in mind, that
the emissions estimated were based on the assumption on
3. Results and discussion
the nitrogen content in influent, treatment efficiencies,
and the calculation methods for N2O-emissions. There­ 3.1. Global warming
fore, there is strong uncertainty associated with N2O – As the results of this study were used in the planning of a
emissions. new carbon-neutral urban settlement, the climate change
Nitrogen and phosphorous in the sludge have value as impact was of special interest. The combination of water
a fertilizer, and can substitute the use of mineral treatment, piping and pumping of potable water, piping
fertilizers in agriculture. There are, however, several and pumping of wastewater, and wastewater treatment had
quality criteria for sludge, which separate it into three an annual total impact of 8.2 million CO2-eq, or 48 kg
categories: sludge for agriculture, sludge for greening, CO2-eq per capita. The WWTPs had the largest impact
and sludge for deposition. It is uncommon to incinerate (54%), with multiple sources like energy and chemical use
sludge from WWTPs in Norway, and this is not done in (iron chloride), N2O – emissions, and use of materials
Trondheim either. Of the 4155 tons of sludge from (Figure 3). Energy use contributed to 37% of the total
HØRA, 83% was used in agriculture, 16% was used for impact on climate change for the entire system and was the
greening, and 1% was deposited. At LARA, of the 4309 most important contributor in the water treatment plant,
 328 H. Slagstad and H. Brattebø

Climate change
16
14
12

kg CO2 – eq/cap.
Fer tiliser replacement
10
N2O
8
Transpor t
6
Other materials
4 Chemicals
2 Buldings+pipelines

0 Energy

–2

IV
A
ag
e es ps es R
A A
-V or el
in um el
in Ø LAR
st p p p H -
TP d pi er rp
i -
W an er at te TP TP
at w W
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ps te w a W
W W W
um as te
p W as
er W
at
W

Figure 3. Climate change from the water and wastewater system in Trondheim (171,000 persons).

water and wastewater pumps, and the HØRA wastewater (2004) found that increased water demand management,
treatment plant. energy efficiency, energy generation, and additional
At LARA, emissions due to production of chemicals energy recovery from bio-solids improved all environ­
were more important, as this plant uses chemicals for mental. Guest et al. (2009) and Larsen et al. (2009), on the
treating the wastewater and in addition delivers energy to other hand, call for a paradigm shift in wastewater
the district heating system in Trondheim. Therefore, some handling. They propose improving resource recovery by
of the energy retrieved from biogas production at LARA moving away from conventional end-of-pipe solutions to
offsets the impact from other energy sources. When source-separation technologies. Remy and Jekel (2008),
upstream and downstream impacts were compared, the by contrast, found that source-separation of wastewater
upstream contribution to global warming was found to be does not necessarily result in a system with less
17 kg CO2-eq per capita annually (35%), while downstream environmental impact. Moreover, with the help of MFA
impact was 31 kg CO2-Equation (65%). Water and and LCA, Jeppsson and Hellstrom (2002) also found it
wastewater pumps and storage contributed to 16% of the difficult to prioritise between high-tech, end-of-pipe
total impact, while the pipelines contributed 12%. The solutions and source-separation strategies. Obviously,
infrastructure of the water and wastewater system therefore there are no easy solutions for reducing the impact on
contributed significantly to the total impact from the climate change from these systems, and according to our
system, which is similar to the findings of Lassaux et al. study, concerns other than water-related greenhouse gas
(2007). emissions are more important to address in the planning of
The normalisation value in ReCiPe for climate change a carbon-neutral settlement.
is 11.2 tonnes of CO2-eq annually per person in Europe,
while according to Hertwich and Peters (2009) Norwe­
gians have an annual carbon footprint of 14.9 tonnes of 3.2. Other environmental impacts
CO2-eq per person. The contribution from the water and In a water and wastewater system there is a variety of
wastewater system to the annual total impact per person environmental impact categories that should be con­
was in both cases less than 1%. In the planning of a new sidered. However, from our results it can be seen that
carbon-neutral settlement the impact from the water and ozone depletion, photochemical oxidant formation,
wastewater system, if connected to the conventional particulate matter formation, terrestrial acidification,
system, is of minor importance. Improvements in impact mineral resource depletion, and fossil resource depletion
may be possible, however, by reducing the impact of the all had less than a 1% impact compared to the European
entire system or by introducing alternative local solutions average per-capita impact. The WWTPs contributed to
with reduced environmental impacts. When examining the more than 45% of the impact in each category;
water and wastewater system in Sydney, Lundie et al. nevertheless water treatment, pumping and pipelines
 Urban Water Journal 329

Environmental impact
6000

5000

Normalised impact (PE) 4000

WTP-VIVA
Water pumps and storage

Water pipelines
3000
Wastewater pumps
Wastewater pipelines
2000
WWTP - HØRA
WWTP - LARA
1000

0
CC OD POF PMF TA FE MRD FD
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Figure 4. Normalised environmental impact, relates to 171,000 inhabitants in Trondheim. Climate change (CC), ozone depletion (OD),
photochemical oxidant formation (POF), particulate matter formation (PMF), terrestrial acidification (TA), freshwater eutrophication
(FE), mineral resource depletion (MRD) and fossil resource depletion (FD).

construction were all contributing to the total impact from instead only gives an estimate on the potential for
the system in each category (Figure 4). eutrophication, and without local or regional parameterisa­
The LCA identified freshwater eutrophication as by far tion. This problem is an acknowledged one, and work is
the most important impact category. In the case of currently done in the international LCA community to
Trondheim, the wastewater effluent and overflow was develop parameterised LCA-tools that use regional/local
discharged more or less directly to a seawater fjord (see characterisation factors. Until such LCA- tools are
Figure 2). Therefore, the LCA freshwater eutrophication available, interpretation of LCA results in accordance
impact values are not a result of direct emissions from with local conditions is very important when analysing
wastewater, but mainly a consequence of indirect emissions impacts from urban water and wastewater systems.
from coal mining in the production of electricity, due to the Figure 5 shows how the normalised total environmen­
coal share of the Nordic electricity mix. Hence, local tal impact is distributed between the different parts of the
freshwater eutrophication does not have the potential to be a water and wastewater system. This is actually the same
local urban pollution problem in Trondheim itself, but data as given in Figure 4, but presented in a different way
elsewhere in the value chain of electricity production. for a clearer illustration of the relative importance of each
Marine eutrophication results are not included in part of the system. Figure 6 shows the importance of
Figure 4. However, our calculations showed that this was different resource inputs.
the category with the theoretically largest environmental The results presented in Figures 4, 5 and 6, as a whole,
impact potential, since only a small part of the nitrogen provide an excellent demonstration of the usefulness
content in wastewater is removed in the wastewater of LCA, when aiming for system-wide environmental
treatment plants in Trondheim. Eutrophication problems improvements within an urban water and wastewater system.
may occur in a marine fjord if this has little access to fresh, First, the LCA method clearly demonstrates that
oxygen-rich water. In the case of the Trondheim fjord, several environmental impact categories should be paid
however, this is not a concern, as it is 130 km long, several attention to in the urban water sector. A common priority
hundred meters deep, and with excellent exchange of fresh of water utilities is reduced pollution of local receiving
seawater with the outside Norwegian Sea. Thorough waters by use of advanced wastewater treatment plants.
investigations of the fjord have demonstrated that it has This case study for Trondheim shows that such a priority is
excellent environmental conditions, except some local sometimes not a good strategy, when dealing with
environmental hazard issues originating from other sources receiving waters of excellent quality. Moreover, it is
(Oceanor 2003). The conclusion is therefore that the somewhat unexpected to find that indirect emissions from
effluent from WWTPs in Trondheim can be safely emitted the production of chemicals, pipelines and energy give
as it is, without a need for investing in improved high-grade such high potential impacts regarding freshwater eutro­
treatment. As explained earlier the present LCA method­ phication elsewhere (i.e. not locally) in the overall system.
ology does not take local conditions into account, but Another and more recently common environmental
 330 H. Slagstad and H. Brattebø

Total environmental impact

FD
5000

Normalised impact (PE)

MRD
4000
FE
3000 TA

2000 PMF
POF
1000
OD
0
CC
VA e ps es

es

A
I ag lin

AR
or m

lin
-V

Ø
st pu e

-L
pe
ip

-H
TP er
d rp

pi
at

TP
W an

TP
te

er
w

W
ps a

W
at
te w

W
W as

W
m te
rp
u W as
e W
at
W
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Figure 5. Normalised environmental impact – contribution of different parts of the system.

priority in the water sector is climate change mitigation, A significant reduction in environmental impact for the
and the search for solutions to minimise system-wide urban water and wastewater system in Trondheim would,
greenhouse gas emissions. Our results strongly support theoretically, only be possible by a reduction and/or a shift
a focus beyond that of climate change, which represent in use of chemicals and energy. None of these alternatives
only a small part of the total life- cycle environmental are likely in reality, since the use of chemicals and energy
impact. is already optimised according to cost-benefit criteria in
Second, LCA results clearly point towards what are the the treatment plants and since Norway already has a low-
environmentally most important parts and resource inputs carbon electricity mix. This situation may be rather
of the system. In the case of Trondheim, treatment plants different for cities in other countries, with a more carbon-
for water (VIVA) and wastewater (HØRA and LARA) intensive electricity generation system and with less robust
together represent 66% of the total environmental impact, receiving waters. Hence, in such situations it may be
with the majority on the wastewater treatment side. These important to optimise the urban water and wastewater
findings are in line with those from other studies system, from a total environmental impact perspective,
mentioned earlier in this paper. When examining the by performing a trade-off between how much pollution is
environmental impact contributions from different discharged to the receiving waters, what type of and how
resource inputs, see Figure 6, the clearly important ones much chemicals are used, and how much net energy is
are chemicals, pipeline materials and energy. Also this is consumed after taking into account also the possibilities of
in line with findings from other studies mentioned earlier. energy recovery from wastewater and sludge treatment.

Total environmental impact

5000 FD
Normalised impact (PE)

MRD
4000
FE
3000 TA

2000 PMF
POF
1000
OD
0 CC
t
gy es al
s
al
s
ti on 2O en
er el
in ic er
i
ta N
En p m at r em
pi he po lac
s+ C e rm ns ep
g th a r
in Tr r
ul
d O
lize
B rti
Fe

Figure 6. Normalized environmental impact – contribution of different resource inputs.

 Urban Water Journal 331

The LCA method would provide needed inputs to such a tailings from coal and lignite mining. In terms of
trade-off process. freshwater eutrophication, the LCA results were therefore
very sensitive to the electricity mix.
Nitrous oxide contributes to 18% of the climate change
impact category; however, great uncertainties are involved
3.3. Uncertainty when calculating the climate change impact of nitrogen in
Dealing with uncertainty is a necessary part of using LCA the effluent. This is both due to the lack of accurate data on
to help model systems. Many factors can affect the results nitrogen content in the effluent and the uncertainty stated
of an LCA, such as choice of inventory (LCI) and impact by the IPCC on the emission factor of N2O (IPCC 2006).
assessment (LCIA) methodology, system boundaries, and IPCC estimates the emission factor for N2O to be within
processes within the system. There can also be the range of 0.0005 to 0.25. The consequences of change in
uncertainties in the parameters and assumptions included emission factors were calculated in accordance with the
in the assessment. Energy use is an important contributor IPCC uncertainty range. A change in emission factor from
to the total impact of the system, and the choice of 0.005 to 0.0005 had minor influence on the results,
electricity mix will therefore have some influence on the however, a change to 0.25 increased the total impact on
environmental impact. The Nordic electricity mix climate change by more than six times. Bange (2006)
(NORDEL), used in this study is a fairly ‘clean’ discussed nitrous oxide emissions in European coastal
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electricity mix due to its high share of hydropower. In waters, and he concluded that estuaries and fjords have
order to test the sensitivity of the results to the choice of large emissions of N2O to atmosphere, while open coastal
the electricity mix, the electricity mix for Central-Europe areas were close to in equilibrium with the atmosphere.
(CENTREL) was also considered. When compared to the The situation in the Trondheimsfjord is not estimated,
NORDEL mix alone, the inclusion of CENTREL doubled however.
the impacts of climate change, photochemical oxidant The wastewater treatment plant HØRA today does not
formation, particulate matter formation, terrestrial acid­ fully meet the requirements for removal of suspended
ification, and fossil resource depletion (Figure 7). The solids, and it has therefore been discussed to introduce
total impact in these categories was still small, however, chemical treatment at this plant. If this is implemented,
vis-à-vis the average annual impact per person. Of using iron chloride, the impact on ozone depletion,
particular interest is that the impact of freshwater freshwater eutrophication, and metal depletion would
eutrophication was found to be almost ten times higher increase with between 70% and 165%. The impact on
with the use of the CENTREL electricity mix, due to its climate change would also increase, but not in the same
higher share of electricity generated from coal. This is range. An increased level of wastewater treatment (i.e.
caused by runoff from surface landfilling of spoil and aiming for higher removal efficiencies) will in most cases

Sensitivity

50000

45000
Normalised impact (person equivalents)

40000

35000

30000 Base scenario

CENTREL el.mix.
25000
Low N2O-emission factor
20000
High N2O-emission factor
15000 Chemical treatment HØRA

10000

5000

0
CC OD POF PMF TA FE MRD FD

Figure 7. Sensitivity to change in electricity mix, N2O-emission factor and wastewater treatment.
 332 H. Slagstad and H. Brattebø

consume more energy and chemicals, and as a This large increase is mainly a result of nutrient
consequence increase the impact on climate change. This runoff from landfilling of spoil and tailings from
is an example of practical trade-offs, where the water coal and lignite mining. Such a shift to a more dirty
utilities have to decide what are the most important electricity mix would also give higher climate
objectives in their environmental policy. change impacts.
Situations of poor raw water quality, water scarcity
Local conditions are obviously very important in some
and sensitive receiving waters would change the choice of
LCA studies, and the ReCiPe model with general
technologies in the water and wastewater system a lot,
characterisation factors does not reflect these conditions
and thereby also the results from an LCA study. Poor
faithfully. For the case presented in this paper, marine
water quality would imply more extensive water
eutrophication was considered to represent a minor
treatment. Water scarcity would give more attention to
problem for emissions into a local seawater fjord, despite
water savings, use of alternative water sources and pipe
the results derived from the LCA calculations. This,
rehabilitation in order to avoid water leakages. Discharge
together with great uncertainty in N2O-emissions, was a
to a sensitive freshwater lake/river would require more
central challenge when interpreting the LCA results within
extensive wastewater treatment for extended phosphorus
a local policy framework for future wastewater treatment
removal, while a sensitive fjord would require introduc­
strategies in Trondheim.
tion of nitrification/denitrification for improved nitrogen
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In the planning of a new carbon-neutral urban

removal.
settlement in Trondheim, the results of this study indicate
that the existing water and wastewater system is low in
4. Conclusion climate change impacts, and such a new urban settlement
should rather look for greenhouse gas emission reductions
The objective of this study was to examine the system-
outside the water sector. However, if urban water utilities
wide life cycle environmental impact potentials of
in general wish to minimise their impact on climate
operating the water and wastewater system in Trondheim,
change, they should prioritise the optimisation of chemical
in order to clarify the relative importance of different
and energy usage, mainly in wastewater and water
environmental impact categories and how different
treatment plants. This would have to be done in a trade-off
elements of the water and wastewater system contribute
with respect to a change in treatment efficiencies and
to these impacts. The assessment provided good insight
discharge of pollutants to the receiving water bodies.
into the relative importance of different environmental
Water and wastewater systems in different cities will
impact categories, and what parts of the system and which
be subject to different local conditions regarding raw water
resource inputs to the system contributed the most to each
quality, water scarcity and the robustness of receiving
impact category, and to the total environmental impact.
waters. Water utilities in different cities will therefore
The following conclusions could be drawn:
have to face different environmental challenges and
priorities. LCA can be used to identify what are the most
. The contributions to climate change from the water
important impact categories within the system, where in
and wastewater system in Trondheim is of minor
the system these impacts are created and what are their
concern, compared to the total annual per capita
sources. All this is vital information when urban water
greenhouse gas emissions. With a total impact of 8.2
utilities need to understand how to improve the
million kg CO2-eq annually or 48 kg CO2-eq per
environmental performance of their services.
person, this is less than 1% of a person’s annual
impact on climate change.
. The wastewater treatment plants contributed most
(54%) to the total impact on climate change.
. Freshwater eutrophication, due to the consumption References
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 334 H. Slagstad and H. Brattebø

Apppendix
Processes and impact factors included in the assessment:

Process in Simapro Changes made to processes

B1 Water works/CH/I U
B2 Pump station CH/I U
B3 Water storage CH/I U
B4 Wastewater treatment plant class 2/CH/I U
C1 Carbon dioxide, liqiud at plant/RER U Electricity: NORDEL
C2 Sodium chloride, powder, at plant/RER U Electricity: NORDEL
C3 EDTA, ethylenediaminetetraacetic acid, at plant/RER U Electricity: NORDEL
C4 Iron (III) chloride, 40% in H2O, at plant/CH U Electricity: NORDEL
D1 Diesel burned in building machine
E1 Electricity, medium voltage, production NORDEL, at
grid/NORDEL U
E2 Light fuel oil burned at boiler, non-modulating 100 kW/CH U Electricity: NORDEL
E3 Heat, at cogen with biogas engine, allocation exergy/CH U Biogas production removed
E4 Heat, light fuel oil, at boiler 100 kW, non-modulating/CH U
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E5 Heat softwood logs, at wood heater 6 kW/CH U

E6 Natural gas burned in gas turbine/GLO U
E7 Diesel, at regional storage/RER U
F1 Single superphosphate, as P2O5, at regional storage/RER U
F2 Urea, as N, at regional storage/RER U
M1 Silica sand, at plant/DE U
P1 Polyvinchloride, at regional storage/RER U Extrusion and transportation added
P2 Poluethylene, granulate at plant/RER U Extrusion and transportation added
P3 Steel, low alloyed, at plant/RER U Drawing of pipes added, scrap content
and transport adjusted
P4 Cast iron at plant/RER/U Metal product manufacturing added,
scrap content and transport adjusted
P5 Concrete blocks at plant/DE U Electricity: NORDEL, transport added
P6 Copper product manufacturing, average metal working/RER U Transport added
P7 Glass fibre, at plant/RER U Extrusion and transportation added
T1 Transport, lorry . 32t, EURO5/RER U
T2 Transport, lorry 3.5-7.5t, EURO5/RER U
T3 Transport barge/RER U
X1 Blasting/RER U
Other characterization factors included
R1 Phosphorous contribution to marine eutrophication
R2 Nitrogen contribution to marine eutrophication
R3 N2O contribtution to global warming

Water
Processes included pumps and Wastewater Wastewater
in the assessment VIVA storage Water pipes pumps pipes HØRA LARA
Energy E1 E1 E1 E1, E2, E3 E1, E3, -E1,
-E4, -E5,
-E6
Pipes P1, P2, P3, P4, P1, P2, P4, P5,
P5, P6, P7, D1 P7, D1
Buildings and equipment B1 B2, B3 B2 B4, X1, E7, T1 B4, X1, E7,
T1
Chemicals and material C1, C2, M1 C3 C3, C4
Transportation of T1, T2, T3 T1, T2, T3 T1, T2
chemicals and material
Nitrogen/phosphorous R1, R2, R3 R1, R2, R3
Fertilizer -F1, -F2 -F1, -F2