Application of Life Cycle Assessment (LCA) to Water Purification Facilities
: Inventory Analysis for Comparison Between
“Coagulation Sedimentation + Sand Filtration” and “Membrane Filtration”
Dr. Masahiro Fujiwara*1, Mr. No Hayashi*2, Mr. Kiyotaka Kanai*3, Mr. Masahiko Kiyozuka*4,
Prof. Yoshihiko Matsui*5, Mr. Kosuke Mori*6, Mr. Yasuyuki Sakakibara*7
*1 Japan Water Research Center, 2-8-1, Toranomon, Minato-ku, Tokyo, 105-0001, Japan. [email protected]
*2 Japan Water Research Center, 2-8-1, Toranomon, Minato-ku, Tokyo, 105-0001, Japan. [email protected]
*3 Japan Water Research Center, 2-8-1, Toranomon, Minato-ku, Tokyo, 105-0001, Japan. [email protected]
*4 Japan Water Research Center, 2-8-1, Toranomon, Minato-ku, Tokyo, 105-0001, Japan. [email protected]
*5 Environmental Engineering, Hokkaido University, N13W8, Sapporo, 060-8628, Japan. [email protected]
*6 Ebara Corporation. 1-6-27, Konan, Minato-ku, Tokyo, 108-8480, Japan. [email protected]
*7 Nihon Suido Consultants Co., Ltd, 22-1, Nishi-Sinjyuku 6, Shinjyuku-ku, Tokyo, 163-1122, Japan. [email protected]
Life Cycle Assessment (LCA) is an established method to assess environmental impacts of various human
activities. There are some application examples of LCA for the assessment of various water purification
processes abroad; however, there are few examples in Japan. The Japan Water Research Center conducted
the study to apply LCA method to water purification processes, mainly about “Coagulation Sedimentation and
Sand Filtration” process and “Membrane Filtration” process, on the “e-Water Project” implemented for three
years from fiscal 2002 to 2004. As the result of the study, the two processes are recognized comparable in terms
of both CO2 emission and energy consumption, while it has previously been believed that “Membrane Filtration”
process is more energy-intensive, compared with “Coagulation Sedimentation and Sand Filtration” process.
Key Words: LCA, e-Water, Sand Filtration, Membrane Filtration, LC-CO2, LC-E
1. Introduction
In Japan, water supply systems are served for an extremely high percentage (approx. 97%) of the population. Public
interest for water service rises more than before. It is demanded that in the 21st century to develop safe water circulation
systems. While a water purification system is intended for the provision of water that is safe to drink is necessary to
sustain human life, it no longer enough to discuss this system only from the viewpoint of supplying safe water. Rather, it
has also become necessary to design the system as a whole to enable the effective use of water, and thereby reduce the
load on rivers and sewer systems. In addition, the system must be so designed as to reduce environmental impacts, for
example through energy saving and the reduction of sludge.
Water supply facilities need a great amount of energy in every aspect of their operations, including water intake,
purification and distribution. Electric power used by all the water supply systems in Japan reaches approx. 7.3 billion
kWh per year (as of 2003)*1. Since these water supply systems consume a large amount of energy, mainly in the form of
electric power, much effort has been made in recent years to implement environmental measures relating to this, or to
promote related studies. For example, a study has been made to evaluate water supply systems from the viewpoint of the
environmental load, focusing on LC-CO2 from existing water source, purification and distribution facilities*2. Studies of
this kind have mainly been made by waterworks utilities to evaluate existing water supply systems from the viewpoint of
strains on the environment. On the other hand, there have been only a few cases in Japan in which an appropriate
purification process was selected by considering the environmental loads in the construction or renewal of a purification
facility, though such an approach has been taken in some of instances in foreign countries*3. Accordingly, the authors
have studied LC-E and LC-CO2 with a focus on “Coagulation, Sedimentation & Sand Filtration,” one of the most
conventional purification methods, and presented a case in which an estimation was made by incorporating some indices
on environmental load, to be considered when constructing or renewing a purification plant*4.
Moreover, while membrane filtration facilities, seen as a next-generation purification technology, have been introduced
actively in recent years, it is thought that these facilities should be defined more clearly not only in terms of the stability
of purification and the ease of maintenance and control, but also from the viewpoint of environmental load. In this paper,
we present a case study in which inventory analysis, as an element of life cycle assessment (LCA), was applied to a
selection of purification processes, choosing from the two alternatives; “Coagulation Sedimentation & Sand Filtration”
and “Membrane Filtration,” with materials, construction, operation, maintenance and control as the objects of evaluation.
This study constitutes part of the e-Water Project (The Research and Development on Environmental, Ecological, Energy
saving and Economical Water Purification System). This project was implemented by the Japan Water Research Center
through the cooperation of Companies, waterworks utilities and universities, using a subsidy for scientific research
projects granted by the Ministry of Health, Labour and Welfare.
2. Study Method
2.1 Object and Scope of Study
The study object is shown in Tab. 1. It is generally assumed that while “Coagulation, Sedimentation & Sand Filtration”
provides an economy of scale, there is little room to achieve such an economy in membrane filtration. In view of this, we
chose, as our study object, a hypothetical purification plant with a treatment capacity of 20,000 m3/day*1 (the average
scale for the rapid filtration method in Japan), and assumed that the plant was to be constructed in a mountainous area,
use of gravity to intake and distribute the water. Regarding the purification method, this study involved both of
“Coagulation, Sedimentation & Sand Filtration” and “Membrane Filtration” facility which represent the purification
processes typically used for water supply systems in Japan.
Generally, a “Coagulation, Sedimentation & Sand Filtration” facility consists largely of reinforced concrete structures,
while a membrane filtration facility uses equipment that is more mechanical in nature. Accordingly, it is thought that for
“Coagulation Sedimentation & Sand Filtration,” costs related to transportation during construction, and demolition of the
facility, as well as the amount of chemicals to be dosing, may be higher than for a “Membrane Filtration” facility.
However, since the present study was aimed at to find out a calculation method of the two water purification processes, it
does not cover the subjects related to transportation during construction and the production and transportation of
chemicals that used water purification process, as well as the demolition and disposal of a facility; it was assumed that
regarding these factors, there was little difference between the processes for the purposes of the study.
Tab.1 Object and Scope of Study
Coagulation, Sedimentation & Sand filtration
3
Treatment Capacity: 20,000m /day. Constructed in a
Basic Items mountainous area. Divided into two lines. Use of gravity to
intake and distribute the water
Membrane Filtration
ditto
Coagulation, Sedimentation, Sand filtration, Clean water
reservoir, Discharge basin, Concentration basin, Control
building, Control equipment, Telemeter, Power equipment,
Calculation
Electric power distribution system, Electric power generator,
area
Chemical dosing equipment and its Civil / Mechanical/
Electrical equipment. These construction (initial) and running
stage
Coagulation, Control building, Control
equipment, Telemeter, Power equipment,
Electric power distribution system, Chemical
dosing equipment and its Civil / Mechanical/
Electrical equipment. These construction
(initial) and running stage
Flash
mixer:
1set/1line,
Flocculator:
2sets/2line,
Sedimentation equipment: inclined Parallel plates: 2sets,
Sediment collection equipment: 2set/ 2lines, Rapid sand
filetr: Fix type surface wash equipment 8 basin, Air
compressor: 2sets, Sodium hypochloride dosing equipment:
Pre- and post-chlorination with small tank for delivery, Poly
aluminum chloride dosing equipment with small tank for
delivery, Sediments collection equipment: 2sets
Flash mixer: 1set/1line, Membrane filtration
equipment (with Pump, Back washing water
pump, Air compressor): 4sets, Sodium
hypochloride dosing equipment: Pre- and
post-chlorination with small tank for delivery,
Poly aluminum chloride dosing equipment
with small tank for delivery
Treatment
methods
2.2 Study Method
Methods used for LCA include the unit process analysis method, the input-output analysis (inter-industry relationship)
method, and a combination of these methods (hybrid analysis method). The unit process analysis method involves
enumerating as many elements as possible which relate to materials, processing, transportation, assembly and the like, of
an object of study; and determining the overall environmental impact by multiplying the amount of each element by a
separately determined embodied intensities (units) and totaling the products thus obtained. While this method is based on
a concept that is clear and easy to understand, it is very labour-intensive, due to the need to identify a large number of
elements.
The input-output analysis method involves using a table of inter-industry relationship (input-output table), as well as
separately determined embodied intensities (units), to convert the exchange of money into products, and thereby
estimating the direct and indirect impacts of each element on the environment. This table describes financial exchanges
among industrial sectors engaged in economic activities. In evaluating the environmental load that occurs due to
activities in a certain industrial sector, this method makes it possible to cover not only the load stemming directly from
the sector, but also the indirect load which the sector induces other sectors to cause. On the other hand, it is not clear
whether this method can be sufficiently precise when applied to a purification facility composed of numerous materials,
because only about 400 sectors are covered by the input-output table, which serves as the basis for clarifying the pattern
of industrial exchanges.
In consideration of these points, we adopted the unit process analysis method for the present study, and enumerated as
many materials as possible which was used for the object purification facility.
2.3 Embodied Intensities Used for the Study
Tab. 2 shows the major embodied energy and CO2 emissions intensities used in the present study.
These embodied intensities basically stem from existing reference materials. We also used these reference materials to
establish independent basic embodied intensities (units) based on our survey of items if the basic embodied intensities are
not available. The latter basic embodied intensities were determined by converting units for inter-industry relationship
into those for the unit process analysis method. Those were using a table of producer prices (as of 1995) included in data
on units for inter-industry relationship (“Embodied Energy and Emission Intensity Data for Japan Using Input-Output
Tables” i.e. 3EID database) published by the National Institute for Environmental Studies (an Independent
Administrative Institution). For items which did not have detailed information available, calculations were made using
data that was assumed to approximate true data to the maximum extent possible. For example, data for the sector
classification “special steels” was used as for “silicon steel plate” and “stainless steel,” to adhere to this principle.
Tab.2 Major embodied energy and CO2 emissions intensities used in the present study
Items
Energy
CO2
3
*5
62.97 kg-C/m
Ductile Iron pipe
25.7 MJ/kg
*5
0.987 kg-C/kg *6
Reinforcing bar
25.7 MJ/kg
*5
0.256 kg-C/kg *6
Steel pipe
25.7 MJ/kg
*5
0.391 kg-C/kg *6
915.5 MJ/kW
*9
22 kg-C/kW *9
28.2 MJ/kg
*9
0.401 kg-C/kg *9
11.3 MJ/kg
*9
0.120 kg-C/kg *9
Telemeter: Parts
67.6 MJ/kg
*9
1.746 kg-C/kg *9
Telemeter: assembly
27.0 MJ/kg
*9
0.524 kg-C/kg *9
Controller: Parts
30.7 MJ/kg
*9
0.454 kg-C/kg *9
Controller: Assembly
Power generator: Parts
12.3 MJ/kg
29.5 MJ/kg
*9
*9
0.136 kg-C/kg *9
0.457 kg-C/kg *9
Concret
Electric motor
High-low voltage
electricity board: Parts
High-low voltage
electricity board:
Assembly
2.020 MJ/m
3
*6
Items
Power generator:
Assembly
Apparatus receipt
board: Parts
Apparatus receipt
board: Assembly
Electric wire & cable
Electric wire &
cable: Assembly
Transformer board:
Parts
Transformer board:
Assembly
Energy
CO2
11.8 MJ/kg *9
0.137 kg-C/kg *9
30.7 MJ/kg *9
0.454 kg-C/kg *9
12.3 MJ/kg *9
0.136 kg-C/kg *9
103.7 MJ/kg *9
1.888 kg-C/kg *9
41.5 MJ/kg *9
0.566 kg-C/kg *9
47.3 MJ/kg *9
1.379 kg-C/kg *9
18.9 MJ/kg *9
0.414 kg-C/kg *9
Auxiliary relay
34.6 MJ/kg
board: Parts
Auxiliary relay
13.8 MJ/kg
board: Assembly
RC: Factory
2
9266.3 MJ/m
building
RC: Office building 12523.9 MJ/m2
Electric power
9.45 MJ/kWh
*9
0.531 kg-C/kg *9
*9
0.159 kg-C/kg *9
*7
192.5 kg-C/m
2
*7
2
*7
247.6 kg-C/m *7
*5 0.105 kg-C/kWh *8
Tab.3 System boundary for Basic unit computed by original investigation（calculation method）
System boundary（calculation method）
The main materials which constitute the electric installation per unit weight were enumerated, and it calculated by the
energy/CO2 per unit weight which was obtained from the “input-output table.”
The fixed rate of the energy/CO2 about a material computed having assumed that it was consumed in assembly prosess.
2.4 Period of Lifecycle
In LCA-based evaluation, it is necessary to establish the lifecycle of each relevant facility. In the present study, we
referred to legal service lives to determine the lifecycles of non-mechanical structures, mechanical equipment, electrical
equipment and general building equipment as 60 years, 15 years, 20 years and 50 years respectively.
2.5 Structuring of the Study Object
Based on the hypothetical specifications of the purification facility used as our study object, we enumerated
approximately 1,500 elements related to materials and equipment constituting the facility, as well as to facility operation.
These elements are tabulated in Tab. 4. The unit process analysis method was used to obtain totals for the
Large
and
middle sector classifications.
Tab.4 Structuring of the Study Object
Sector
classifications
Large
Structure
Middle
Sedimentation, Filtration basin
Receiving well
Clean water reservoir
Discharge basin, Concentration
basin
Pipes
Site formation works
Maintenance construction
Chemical mixing chamber
Chemical dosing equipment
Sedimentation & Filtration basin
Machine
Construction
Membrane equipment
(Initial)
Membrane module
Discharge basin, Concentration
basin
Telemeter & Control equipment
Power / Control
Electricity
Telemeter & Control equipment
Receiving & Transformation
Building
Generator
Sedimentation, Filtration basin
Discharge & Concentration basin
Dehydrator
Control building
Chemical mixing chamber
Sedimentation & Filtration basin
Machine
Operation
(Running)
Electricity
Membrane equipment
Discharge basin, Concentration
basin
Power / Control
Telemeter & Control equipment
Receiving & Transformation
Generator
Small
Pipes, Valves, Reinforced concrete, Earthwork
Pipes, Valves, Reinforced concrete, Earthwork
Pipes, Valves, Reinforced concrete, Earthwork
Pipes, Valves, Reinforced concrete, Earthwork, Composite works
Pipes, Valves, Earthwork
Pipes, Valves, Reinforced concrete, Earthwork
Reinforced concrete, Earthwork
Rapid Mixing machines
Pumps, Mounts, Pipes, Valves, Meters, Tanks
Trough, Flocculator, Pumps, Sediments collection equipment, Pipes,
Valves, Inclined parallel plats, Incidental facilities, Air compressors,
Sand, Gravel, Water collection devices, Back washing equipment,
Discharge equipment, Composite works, Water conveyance devices
Pump, Pipes, Valves, Incidental facilities, Air compressors, Composite
works
Casing, membranes
Pumps, Sediments collection equipment, Mounts, Pipes, Valves
Water supply equipment
Cable ducts, High-low voltage electricity boards, Cables, Auxiliary relay
boards
Controllers, Telemeters, High-low voltage electricity boards, Apparatus
receipt boards, Cables, Meters
High-low voltage electricity boards, Generator connection boards,
Primary transformation boards, Cables, Transformation boards
High-low voltage electricity boards, Generators, Cables
Building
Building
Building
Building
Rapid mixers
Flocculators, Sediments collection equipment, Incidental facilities, Air
compressors, Pumps
Replacement of pumps, Air compressors, Membrane modules,
Pumps, Sediments collection equipment, Incidental facilities, Air
compressors, Pumps
Auxiliary relay boards
Electric power
Generator connection boards, Primary transformation boards,
Generator boards, Main boards, Receiving boards, Condenser boards
Middle load Switches, Power supply boards, Transformer boards
Generators, Automatic starting boards, Generator boards
* In actual calculation, data (dimensions and quantities) on the elements was categorized as “details” under the above sector classification.
3. Study Results
Generally, a purification facility has auxiliary equipment. This applies especially to membrane filtration; the facility
therefore can meet the maximum demand for filtration even during the washing of membrane modules using back flow
or chemicals. Since the actual amount of water treated at a facility is usually different from its maximum treatment
capacity, a correction factor (operation ratio) is necessary for calculation. In this study, calculations were made on the
supposition that each facility constantly treated 20,000 m3 of water per day.
3.1 Lifecycle CO2 Emissions
Fig. 1 shows the total lifecycle CO2 (LC-CO2) emissions for the large sector classification. Regarding the amount of
LC-CO2 occurring per year, non-mechanical structures during construction rated high for “Coagulation Sedimentation +
Sand Filtration.” It was 17.4 g-C/m3 altogether. For membrane filtration, mechanical equipment during construction and
operation rated high. It came to 9.6 g-C/m3 in all. This is presumably because non-mechanical structures account for a
greater portion of a conventional water purification facility, in comparison to that of another. However, this difference
becomes smaller if more consideration is given to items that were regarded as introducing no significant differences.
Because calculation conditions of both water purification methods were different, and above results cannot compare
directly. Accordingly, it will probably be wrong to assume that the above-mentioned results indicate a clear difference.
3.2 Lifecycle Energy Consumptions
Fig. 2 shows the total lifecycle energy (LC-E) consumptions for the large sector classification. Regarding LC-E
consumed per year, mechanical and electrical equipment during operation rated high for “Coagulation Sedimentation +
Sand Filtration.” It was 0.98 MJ/m3 in all. For membrane filtration, mechanical equipment during operation rated high. It
came to 0.70 MJ/m3 altogether.
In both types of facility, mechanical equipment during operation rated high. This suggests that maximum efficiency may
be achieved in reducing environmental load by focusing on mechanical equipment during operation.
Construction
(Concrete)
19%
35%
Operation
(Electric)
14%
Construction
(Building)
Sedimentation
& Sand filtration
LC-CO2
17.4
3
g-C/m
Operation
(Machine)
45%
44%
Membrane
Filtration
LC-CO2
3
9.6 g-C/m
Operation
(Electric) 5%
9%
20%
Construction
(Machine)
0%
Construction
(Concrete)
Operation
(Machine)
Construction
(Machine)
Construction
3% (Electric)
Construction
(Electric)
0%
Construction
6% (Building)
Fig.1 Large sector classification by LC-CO2 emissions
0%
Construction
(Concrete)
Operation
(Machine)
Construction
(Machine)
18%
31%
24%
Operation
(Electric)
Sedimentation
& Sand filtration
LC-E
0.93
3
MJ/m
33%
5% Construction
(Machine)
3%
Construction
(Electric)
Operation
(Machine)
57%
Membrane
Filtration
LC-E
0.70
3
MJ/m
Construction
(Electric)
0%
4%
19%
Construction
(Building)
Construction
(Building)
6%
Operation
(Electric)
Fig.2 Large sector classification by LC-E consumptions
4. Conclusion
In this paper, the authors reported the calculation results of “Coagulation Sedimentation + Sand Filtration” and
“Membrane Filtration” water purification processes. The study covered the lifecycle of a purification facility (i.e.
materials, construction, operation, maintenance and control), and involved the calculation of lifecycle energy (LC-E) and
lifecycle CO2 (LC-CO2), based on the application of inventory analysis as an element of lifecycle assessment (LCA).
Conventional wisdom says that a membrane filtration facility consumes much more energy than a facility using
“Coagulation Sedimentation + Sand Filtration” However, The results of the present study show that the former can be
considered as a viable alternative to the latter. However, it should be noted that these results were obtained under the
preconditions shown in Tab. 1. In making calculations for the whole spectrum of water supply systems, it will be
necessary to consider the particular conditions, for these systems have different features and ambient environments e.g.
the raw water quality, purification method, the difference in ground level between the water source and purification plant,
and the geography of the area to be serviced.
Further studies need to be made to determine the desirable features of water supply systems which can contribute to
controlling the environmental impacts. In these studies, it will be necessary to take into account differences in facility
scale and raw water conditions, as well as transportation and disposal or re-use which were not covered by the present
study.
References
*
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*
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*
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*
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*
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*
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*
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*
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