Transcript Dias nummer 1 - Neptune: Welcome to EU Project Neptune

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 Figure 1: Framework diagram
some of the WWTTs.
Raw sewage
input
METHODOLOGY A comprehensive
theoretical framework for carrying out
LCAs of WWTTs has been developed and
streamlined for use in NEPTUNE (www.euneptune.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 sludgespecific 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).
Activated sludge aeration
Primary settler
(Anaerobic denitrification)
Secondary settler
Phosphate precipitation
CASE STUDY 1: REFERENCE WWTP
The plant modelled in this case study and
illustrated in figure 2 represents a capacitybased 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.
Treated water to
river or lake
Grit removal
Activated sludge
Excess activated
sludge
Primary settler
sludge
Chemical sludge
Biogas
Incineration
Sludge heater
Raw sludge
Energy
Anaerobic digestion
Dewatering
Recirculation of digestion effluent
SLUDGE
INCINERATION
Digester sludge
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.
Figure 3: Weighted environmental impact potentials (environmental efficiency view)
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.
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 2:1 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.
1 m3
WW
Primary
Settling
Activated sludge
El
Secondary
Settling
Heat
El
Water
Biogas
+ 0.075 kWh
Co-generation of
Heat and Power
+ 0.075 kWh
El
Heat
Dewatering
Sludge
Incineration
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.
Mesophilic
Anaerobic
Digestion
+ 4 g tot-N
El
Heat
Ashes
Slag
Figure 4: WWTP with primary settler
1 m3
WW
Activated sludge
El
+ 0.1 kWh
Water
Secondary
Settling
Heat
El
Mesophilic
Anaerobic
Digestion
Effluent
Biogas
Co-generation of
Heat and Power
El
Heat
Dewatering
Sludge
Incineration
+ 0.013 kWh
El
+ 0.075 kWh
Heat
Ashes
Slag
Figure 5: WWTP without primary settler
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 ([email protected])