ABSTRACT The EU FP6 NEPTUNE project is related to the EU Water Framework Directive and the main goal is to develop new and optimize existing waste water treatment technologies (WWTT) and sludge handling methods for municipal waste water. Besides

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Sustainable treatment of municipal wastewater
Peter Augusto Hansen Henrik Fred Larsen (DTU
Management, Technical University of Denmark -
Lyngby, Denmark)
ABSTRACT The EU FP6 NEPTUNE project is related to
the EU Water Framework Directive and the main
goal is to develop new and optimize existing
waste water treatment technologies (WWTT) and
sludge handling methods for municipal waste
water. Besides nutrients, a special focus area is
micropollutants (e.g. pharmaceuticals, heavy
metals and endocrine disrupters). As part of this
work a holistic based prioritisation among
technologies and optimisations is to be done.
Tools for this prioritisation include life cycle
assessment (LCA) and cost/efficiency. As novel
approaches, potential ecotoxicity impact from a
high number of micropollutants and the potential
impact from pathogens are to be included. In
total more that 20 different waste water and
sludge treatment technologies are to be assessed.
This paper will present the first preliminary LCA
results from running existing life cycle impact
assessment (LCIA) methodology on some of the
WWTTs.
METHODOLOGY A comprehensive theoretical framework
for carrying out LCAs of WWTTs has been developed
and streamlined for use in NEPTUNE
(www.eu-neptune.org). This framework is based on
EDIP 1997 and models process-, wastewater- and
sludge-specific burdens of WWTTs as illustrated
in figure 1 (Hansen 2008, Larsen et al. 2006).
Note that on this figure, only wastewater-specific
burdens are schematized and sludge-specific
burdens should be considered in the same way. To
illustrate possible applications of the
methodology, preliminary results from the first
two case studies are presented on this poster,
based on data from the EcoInvent database and
NEPTUNE data. Each case study will be assessed
through the concept of environmental
efficiency. Environmental efficiency is
assessed by comparing the environmental impacts
induced by the physical inputs necessary to run
the WWTP (in yellow on figure 1) to the potential
environmental impacts of the water emissions (in
blue on figure 1) avoided by the treatment
process (i.e. impact of influent minus impact of
effluent).
CASE STUDY 1 REFERENCE WWTP The plant modelled
in this case study and illustrated in figure 2
represents a capacity-based average of Swiss
municipal wastewater treatment plants (WWTPs) as
modelled by Doka (2003) for use with the
EcoInvent database. As such, the model is very
comprehensive its physical inventory includes
all infrastructure and operating inputs necessary
to run the WWTP, along with the corresponding
disposal processes. Also, more than 30 parameters
including organic matter, nutrients, heavy metals
and other inorganic substances in the water are
tracked throughout the system and are accounted
for in terms of their fate in air, water and
solid media. This case study is here used as a
reference example showing a rather comprehensive
LCA of a given combination of WWTTs.
Figure 2 Reference typical 3-stage WWTP based
on Doka (2003)
CASE STUDY 1 INTERPRETATION Figure 3 shows the
environmental efficiency profile of the reference
WWTP. Note avoided impacts refer to the
difference between the environmental impact
potentials resulting from releasing raw
wastewater directly into the environment without
treatment, and the impact potentials from
emissions to air, water and soil stemming from
the substances in the wastewater and their fate
after going through the reference WWTP. Induced
impacts refer to the impact potentials resulting
from constructing, operating and disposing of the
WWTP. From this figure, we may conclude that the
environmental efficiency of the reference WWTP is
close to a 21 ratio, meaning that for every
environmental impact induced by this WWTT train,
2 times more impacts are actually avoided thereby
making it a viable WWTT train for treating water
containing the inventoried substances/parameters.
CASE STUDY 2 WWTP WITH(OUT) PRIMARY SETTLING In
the second case study, two similar WWTPs with and
without primary settler are compared, based on
preliminary NEPTUNE data. Figure 4 shows a WWTP
identical to the reference WWTP. Figure 5 shows a
similar system, except without primary settler.
The two WWTPs are compared exclusively on the
basis of their energy consumption and generation
patterns as well as on their capacity to remove
total nitrogen in the water. On the two figures,
processes differing within those parameters
(energy and nitrogen) are highlighted in grey
while differences in energy consumption and
nitrogen removal are highlighted in green
(positive for the environment) and orange
(negative for the environment). Differences in
the infrastructure inventory and other parameters
are disregarded in the comparison.

• CASE STUDY 2 INTERPRETATION Based on figure 4
  and 5, a comparative energy and nitrogen balance
  may be carried out, resulting in the following
  conclusions per functional unit (m3 waste water)
• The WWTP with primary settler releases 4 g tot-N
  more.
• The WWTP without primary settling consumes 0.162
  kWh more.
• Therefore, we may compare both systems by
  comparing the impact associated with nitrogen
  removal vs. electricity consumption, as
  illustrated in figure 6. Since electricity may be
  generated by different means with different
  associated environmental impacts, figure 6
  presents electricity grid mixes corresponding to
  European countries illustrating the range of
  electricity sources available in Europe
• Norway electricity is supplied mainly from
  hydro-power, resulting in generally lower
  emissions to the environment.
• Poland electricity generation is based mainly
  on coal power and as such, results in high
  emissions to the environment.
• From this data, figure 6 and disregarding all
  parameters except nitrogen removal (assuming
  nitrogen limited recipients) and energy balances
  (average electricity approach), we may conclude
  the following
• WWTPs without primary settling achieve a better
  nutrient removal rate although they require more
  energy to operate because of the higher loads
  handled in the biological step
• To select one system over the other based on
  nutrient removal vs. energy balance, the national
  profile of electricity generation technologies is
  important
• For countries with relatively clean electricity
  (e.g. Switzerland), a WWTP without primary
  settling may be a better option.
• For countries with electricity based primarily
  on fossil fuel (e.g. Poland), a standard WWTP
  with primary settling should be preferred. 

• REFERENCES
• Doka G (2003). Part IV Life cycle inventory of
  wastewater treatment. Life cycle inventories of
  waste treatment services EcoInvent report No.
  13. Swiss Center for Life Cycle Inventories,
  Switzerland
• Hansen PA (2008). A conceptual framework for
  life cycle assessment of wastewater treatment
  systems Master thesis, DTU Management, LCA
  Group, Technical University of Denmark
• Larsen HF, Hauschild M, Wenzel H, Almemark M
  (2007). Homogeneous LCA methodology agreed on by
  NEPTUNE and INNOWATECH Deliverable D4.1. EC
  Project NEPTUNE, contract No. 036845
• ACKNOWLEDGEMENT
• This study was part of the EU Neptune project
  (Contract No 036845, SUSTDEV-2005-3.II.3.2),
  which was financially supported by grants
  obtained from the EU Commission within the
  Energy, Global Change and Ecosystems Program of
  the Sixth Framework (FP6-2005-Global-4).
• Corresponding author Henrik Fred Larsen
  (hfl_at_ipl.dtu.dk)