LCA OF DRINKING AND WASTEWATER TREATMENT SYSTEMS OF
BOLOGNA CITY: FINAL RESULTS.
Mario Tarantini, Federica Ferri *
ENEA Via Martiri di Monte Sole 4 40129 Bologna [email protected]
*Ravenna provincial administration, V. Bordella 6 40026 Imola (BO)
[email protected]
Abstract
A pilot study to apply LCA methodology to domestic water cycle of Bologna city is
in course of completion. The activity is being carried out within the AQUASAVE
project, funded by a LIFE-ENVIRONMENT action of the European Union. The
LCA study objective is to develop a model that will allow to compare the overall
environmental impact of the Òexisting scenarioÓ of the drinking and wastewater
treatment systems of Bologna metropolitan area to the Òinnovative oneÓ tested in
AQUASAVE.The final TEAMTMLCA model of the "existing scenario" has been
completed.
In this paper the methodological approach, the limits and advantages of LCA
methodology when applied to urban water cycle and the final results of the study are
discussed.
Life cycle assessment, LCA, urban water cycle sustainability
INTRODUCTION
As part of AQUASAVE project, funded by the European Union in the framework of
the LIFE-ENVIRONMENT action, an assessment of the environmental
sustainability of innovative techniques of water consumption reduction, rain water
harvesting and grey water reuse in a residential building of Bologna city is in
progress. The aim of AQUASAVE project is to design and build an apartment
house in Bologna, to demonstrate trough the introduction of appropriate devices and
technologies, the possibility to save up to 50% of drinking water.
For verifying if substantial environmental improvements can be obtained, a
comparison between the ÒexistingÓ urban water cycle and an ÒinnovativeÓ one, in
which AQUASAVE proposed technologies are applied, is in course of completion.
The Life Cycle Assessment (LCA) methodology has been adopted, due to its
capacity of quantitatively assess the life cycle of products and services. The analysis
of the ÒexistingÓ scenario has been completed and is presented in this paper. The
study has been carried out with the full co-operation of management and engineers
of SEABO, the municipal water firm of Bologna city which is partner of
AQUASAVE project.
METHODOLOGY
The LCA study has been conducted according to ISO 14040 standards.
The goal has been the evaluation of the environmental benefits and burdens of
introducing innovative techniques in the AQUASAVE demonstration building. To
reach this goal the Òexisting scenarioÓ of drinking water production and distribution
and of waste water treatment for the entire Bologna district, has been analysed in
detail. The study has enabled the identification of the main environmental burdens,
helping in proposing potential improvements.
The analysis of the functions of the studied system suggested the adoption of the
following functional unit Òthe supply of a quantity of water of suitable quality for
performing all domestic activities to one person living in Bologna and the treatment
of resulting wastewaterÓ. According to the actual consumption estimations the
reference flux has been assumed to be 180 liters per day (corresponding to 65,7 m3
per year)
GROUND &
SURFACE
WAT ER
DR INKING WATER
TREATM ENT AN D NET
SYSTEM
BOUNDARIES
U RBAN
RU NOFF
D OM EST IC
USE
IN DUSTRIES
CH EM ICALS
EN ERGY
TR ANSPORT
M AT ERIALS
SEW ER NET
IND UST RIAL WASTE
WATER
D RAINS,W EIRS
TREATED
EFFLUENTS
WASTE WATER
TR EATM ENT PLANT
SOLID W ASTE
INC INIR ETOR
WATER
AIR
EM ISSIO NS EM ISSIONS
SOLID
EM ISSIO NS
Fig. 1 shows the adopted system boundaries. The system includes all the processes
for the distribution and treatment of drinking and waste water, the production
processes of chemicals, electric energy and materials used in water treatment plants,
including their transport to the final use location.
The contribution to Life Cycle Inventory of all equipment, waterworks, buildings
and capital goods required in the system for processing and distributing drinking
water and for treating wastewater has not been included in the analysis, as they are
supposed to remain unchanged both in ÒexistingÓ and in the ÒinnovativeÓ scenario.
To model the entire studied system and perform all the inventory and impact
assessment calculation the TEAM 3.0software, developed by Ecobilan, was used.
The data have been collected from various sources. On site specific data have been
gathered for all the drinking water treatments and waste water treatment plant
(WWTP) processes, with the support of SEABO technicians. The main data
collection method for chemicals was by identifying the specific manufacturer of the
commercial product. The processes involved in chemicals manufacture were
identified trough these contacts and as much data as possible regarding the
manufacturing process was obtained. Where specific data were not available,
reference was made to TEAM 3.0 database or to relevant scientific literature.
As the studied system is very complex, several assumption were needed to model it.
In Bologna metropolitan area there are six sources of drinking water (a superficial
one and five wells): It was decided to consider the water entering in the
ÒAQUASAVEÓ residential building as a weighted average of the six sources.
It was assumed that the drinking water provided to the apartments is all discharged
to wastewater collectors and treated inside the wastewater treatment plant.
A number of chemicals are used in the processes: after analysing the products
Material Safety and Data Sheets (MSDS), we verified that no toxic substances are
involved and decided to exclude from the inventory, substances whose cumulative
mass were not greater than 5% of the sum of the input masses (water excluded). This
assumption has been validated by the results of the analysis.
SYSTEM DESCRIPTION
Bologna is an Italian city with 380.000 inhabitants which extends on km2 140 area.
Bologna drinking water comes from five groundwater sources and a superficial one
(Setta river). The contribution of groundwater sources to the total drinking water
mass feeded to the network in one year is about 60%. The groundwater treatment
processes are very simple: a disinfection by mean of ClO2 is in general sufficient.
The water of some well needs a preliminary sand filtration and activated carbon
adsorption is needed.
SETTA RIVER
O3
PREDISINFECTION
COAGULANT
FLOCCULANT
CLARIFLOCCULATION
SLUDGE
SLOW SAND FILTRATION
WASTE
WATER
O3
DISINFECTION
ClO2
POSTDISINFECTION
WATER WORKS
Fig 2 shows the treatment processes of Setta river plant. This plant works
continuously, with a flowrate that changes seasonally depending on the water level
in the river. The Bologna distribution net is very complex and is fed by two water
reservoirs each of m3 40.000 located at the opposite limits of the city and connected
by a backbone piping. Near the two reservoirs sodium hypoclorite is added as
required to ensure the net disinfection.
The Bologna sewer net collects domestic wastewater, as well as urban runoff and
effluents coming from some industries in the area. The most part of the rain water
collected by the sewer net reaches the wastewater treatment plant; in case of
important storms, however, numerous weirs, dispersed in the sewer system,
discharge the water directly into superficial water bodies. The weirs are designed to
ensure the proper dilution factor of the effluents for respecting the allowed
concentration of contaminants.
WASTE
WATER
INT AKE
MAC R OST RA ININ G
M ICR OST RA IN ING
SOL ID W ASTE
IN CIN IRE TOR
GRIT C HAM BE R
DEO ILE R
BIOGA S
PRIM ARY
G RAV IT Y
SEDIMEN TAT ION
T H ICK E NE R
EN GIN E S
B O ILE RS T ORCH
A ER OB IC
D IGEST IO N
O2
G ASE S
B IOL OGICAL
OXIDA T IO N
SL UDGE ST O R AGE
FILT E R PRE SS
SECO N DAR Y
SEDIMEN TAT ION
ST OR AGE
CE N T RIFUGAL
ST O R AGE
PAA
DISINFECT IO N
SL U DGE
INCINIR E TO R
CAN ALE NAVIL E
ASH T O
L AN D IFIL L
G ASE S
Fig. 3 shows the WWTP processes. The plant has a sludge incinerator in which the
combustion heat is recovered and used to increase the input sludge temperature. The
effluents of the plant are treated water discharged to Canale Navile; ashes and
sludge (only when the incinerator is out of order) sent to landfill; sand, oil and
material from straining directly sent to Municipal Solid Waste incinerator; airborne
emissions due to sludge incineration and biogas combustion. The plant has an odour
treatment line: the air over the main treatment stages is collected and treated by
means of a bio-filter.
ALLOCATION
As suggested by ISO 14040 standards, where possible the allocation has been
avoided. Anyway the Bologna WWTP treated in the reference year almost 58
million of cubic meters of water, of which roughly 14% was rain water, 64%
domestic wastewater and 22% industrial wastewater. So, as the urban runoff and the
industries connected to the sewer net were not included in the analysed system, the
impact of WWTP processes was allocated on mass. Moreover, it was decided to do
not consider the presence of metals (zinc, copper, lead, chromium, nickel) in the
treated effluent, in the sludge and in the incinerator emissions, as they can be
clearly related to urban runoff and industries effluents. Substances clearly related to
domestic wastewater (nutrients, tensides, suspended solids, COD, TOC) were
included in the environmental effect analysis .
RESULTS
In this study several environmental impact categories have been investigated and the
processes responsible for the main environmental loads have been identified. The
system has been divided in seven main stages. The stage ÒdistributionÓ includes the
impacts of energy consumption for pumping the water in the net and the sodium
hypoclorite consumption that is used for net disinfection; the stage Òlandfill (special
waste)Ó takes in account the impacts of disposal the ashes coming from the Seabo
sludge incinerator and the sludge from Setta river plant in a landfill for special, non
dangerous wastes; when Seabo incinerator is not operating, WWTP sludge is
disposed in a landfill for urban wastes (stage ÒlandfillÓ); materials coming from
WWTP straining, grit chamber and deoiler are sent to Municipal Solid Waste
Incinerator (stage ÒincineratorÓ).
Energy Indicators
MJ
1000
900
800
E Feedstock Energy
700
E Fuel Energy
600
E Non Renewable Energy
500
E Renewable Energy
400
E T otal Primary Energy
300
Elect ricity
200
100
0
-100
Drinking wat er
t reat ment
Distribution
Waste wat er
treatment
Landfill
Landfill
(special waste)
Incinerat or
Existing water
cycle
Fig 4 shows the energy indicators for the system. It can be observed that the main
energy consumption is related to drinking water treatments and is due to electrical
energy used for water pumping (about 65% of the total energy consumption); the
energy used in WWTP is mainly electrical energy used on site as well. Looking at
the inventories tables it is possible to underline that:
•
•
10% of the primary energy extracted from the environment is required for
chemicals production;
the contribution of transport phases (fuel production and burning) to the total
energy use is irrelevant.
IPCC 1998 - Greenhouse effect (direct, 100 years)
g eq CO2
70000
60000
50000
others
40000
(a) Carbon Dioxide (CO2, fossil)
30000
(a) Methane (CH4)
20000
10000
0
-10000
Drinking
water
treatment
Distribution Waste water
treatment
Landfill
(special
waste)
Landfill
Incinerator
Existing
water cycle
Fig. 5 shows that CO2 and methane emissions are the main contributors (99%) to
greenhouse effect. Both species are mainly released in the electric energy production
processes; the production of the electric energy used on site is responsible for 93%
of the total impacts. The contribution of chemical production is limited to few
percent.
CML 1992 - Air Acidification
g eq H+
24
22
20
18
16
14
12
10
8
6
4
2
0
-2
others
(a) Sulphur Oxides (SOx as SO2)
(a) Nitrogen Oxides (NOx as NO2)
Drinking
water
treatment
Distribution
Waste water
Landfill
treatment (special waste)
Landfill
Incinerator
Existing water
cycle
Fig 6 confirms that the dominant process is the electric energy production. This
process in fact is responsible of 90% of the impacts, mainly trough the emissions of
SOx and NOx (which together have 100% of the impacts). Chemicals manufacturing
contribution is 4% of the effects in this category.
WMO 1998 - Photochemical oxidant formation
g eq ethylene
others
120
(a) Hyd ro ca rbons (e xcept me thane)
100
(a) M e thane (CH4)
(a) P ro pane (C3H8)
80
(a) Hyd ro ca rbons (unspecified)
(a) Ethane (C2H6)
60
(a) Eth ylene (C2H4)
(a) B u tane (n -C 4H10)
40
(a) A lkane (unspecified)
20
0
-20
Drinking water
treatment
Distribution
Waste water
treatment
Landfill
(special waste)
Landfill
Incinerator
Existing water
cycle
Fig 7 shows the contribution of different chemical species to photochemical oxidant
formation. Electric energy production is still the dominant effect (90% of the effects
for the electric energy used on site). Drinking water treatments are responsible of
60% of the impacts.
USES 2 1998 - Aquatic Toxicity
g eq 1-4
dichlorobenzene
25000000
20000000
others
15000000
(a) Vanadium (V)
(w) Barium (Ba++)
10000000
(a) Nickel (Ni)
5000000
0
-5000000
Drinking
water
treatment
Distribution Waste water
treatment
Landfill
(special
waste)
Landfill
Incinerator
Existing
water cycle
Fig 8 shows the environmental effect in the Aquatic toxicity categories. The effects
have been quantified using USES 1998 method developed by CML (Netherlands).
Anyway the analysis has been repeated applying several different methods (CML
1992, CST 1995 and USES 1 1994), in order to confirm the identification of the
critical processes. Each method adopts different reference substances and different
characterization factors, but nevertheless they all agree in identifying by far the
electric energy production as the dominant process. The same procedure has been
applied to human toxicity and terrestrial toxicity impact categories: the results were
very similar.
CML 1992 - Depletion of non renewable resources
frac. of reserve
1,20E-13
1,00E-13
ot hers
8,00E-14
(r) Oil (in ground)
6,00E-14
(r) Natural Gas (in ground)
4,00E-14
(r) Bauxite (Al2O3, ore)
2,00E-14
0,00E+00
-2,00E-14
Drinking
wat er
treatment
Distribution
Waste water
treatment
Landfill
(special
waste)
Landfill
Incinerator
Existing
wat er cycle
Fig 9 shows that the main impacts are due to natural gas and oil consumption for
electric energy production. Electric energy production causes 70% of the impacts.
Chemicals production contributes with 10%, mainly for bauxite needed in the
aluminium based flocculant production.
With regard to water eutrophication category, the discharge in the environment of
the treated effluent is responsible, as can be guessed, for 100% of the impacts.
Normalization
1,80,E-02
1,53,E-02
1,60,E-02
1,40,E-02
1,25,E-02
1,20,E-02
1,00,E-02
8,00,E-03
6,33,E-03
4,88,E-03
6,00,E-03
4,70,E-03
4,00,E-03
2,00,E-03
2,53,E-03
4,46,E-05
0,00,E+00
0,00,E+00
Exaust.
eutroph.
ozone
ecotox.
grenh.
acidif.
s. smog
humantx.
Fig 10 shows the impact of the selected reference flux on each environmental
category divided by the impact of an average European inhabitant over one year
(IVAM ER elaboration of CML 1992 method). Normalization reveals which effects
are large and which are small in relative terms. With this approach the most relevant
effect seems to be eutrophication. Anyway the relative contribution is in the order of
2%, indicating that a well managed WWTP reduces the eutrophication potential to
an acceptable value compared to, for instance, the nutrient release in agricultural
practices.
CONCLUSIONS
In this study the Òexisting scenarioÓ for treatment and supply of drinking water and
for treatment of wastewater in Bologna city has been analysed. By mean of
environmental impact assessment categories well accepted at international level, the
environmental critical processes have been identified. The production of electric
energy mainly used for on site water pumping is by far the most relevant process in
almost all impact categories. Nevertheless in absolute terms, the Òenergy contentÓ of
the water cycle (90 kWh per person per year) is not so impressive, being only a
percentage of the electricity needed in an apartment. The discharge in the water
body of the treated effluent is responsible for 100% of water eutrophication impacts.
Looking at Fig. 10 the contribution of domestic water cycle when compared to the
total contribution of one person is in the order of 2%, indicating that a well managed
WWTP reduces the eutrophication potential to an acceptable value compared to an
average emission of a European citizen. Chemicals production impact is in general
low but not irrelevant: an accurate dosage can reduce the consumed quantity and
consequently the actual impacts. Transport phases and the related fuel production
are irrelevant in all environmental impact categories.
LCA results indicated that to further improve the environmental performances of the
ÒexistingÓ water cycle it is necessary to reduce the energy consumption, optimising
design and operation of pumping devices.
On the other hand water is considered only a renewable natural resource in LCA: but
if local conditions are considered the lowering of water-bearing stratum is the main
responsible of the subsidence phenomenon that has originated a ground lowering of
5-6 centimetres per year in 34% of Bologna metropolitan area. Each action that
brings to a more retionale water use and causes a lower groundwater extraction
should be carefylly evaluated. These considerations shall be taken in account in
weighting the environmental impact categories and in evaluating the suitability of
innovative technologies for rainwater harvesting and grey water reuse.
Aknowledgement
The authors would like to tank Mr. Raffaelli and Mr. Pescari of SEABO spa for their
kind help.
References
Ferri, F, Tarantini, M., AQUASAVE project-Life cycle Assessment of drinking
water and waste water treatments of Bologna city (in Italian) 154 p. ENEA OTSCA-00024 Rev 0
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symposium on Integrated Water Resouces Management, University of California,
Davis, USA
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