Applying Life Cycle Assessment to Drinking Water Treatment

Transcription

1 Applying Life Cycle Assessment to Drinking Water Treatment W.Takashima*, S.Takizawa**and M. Fujiwara* *Japan Water Research Center, Minato-ku, Tokyo, , Japan ** University Of Tokyo, Bunkyo-ku, Tokyo, , Japan Keywords: CO 2 emission, energy consumption, LCA (Life Cycle Assessment), water treatment INTRODUCTION Although LCA (Life Cycle Assessment) is being implemented in many industrial sectors, so far there have been few examples of LCA research or practical applications in waterworks. We applied LCA method to drinking water treatment in order to collect fundamental data and show specific examples of the process for implementation of LCA in selection, planning, and maintenance of water treatment systems at purification plants. This report shows how energy consumption and CO 2 emission depend on each process and stage, i.e. the stage of construction, operation and maintenance, and disposal, of drinking water treatment system through LCA research. The study forms a part of the "Research Into Water Treatment and Pipe Technology Aimed at Establishment of a Safe Water Cycle" subsidized by the Ministry of Health, Labour and Welfare. METHODS Water treatment types covered by this study were flocculation + sedimentation + sand-filtration, membrane filtration, ozonation, and activated carbon treatment. Major specifications of the respective facilities are listed in Table 1. Reference information about weight/volume of materials and equipment was collected from design specifications used for actual purification plant construction. The figures for energy consumption and CO 2 emission per unit weight/volume for each material are based on available published databases and other reference documents. Some figures were directly from some related manufacturers. RESULTS A series of case studies were implemented by applying LCA methods mentioned above. The results are as follows: 1) Flocculation + Sedimentation +Sand-filtration Figure 1, 2 shows LC-E (Life Cycle Energy consumption) and LC-CO 2 (Life Cycle CO 2 emission) amounts for this treatment system for 58 years operation. In construction stage, load caused by civil engineering for concrete structures, etc., makes up the highest figure. The LC-E and the LC-CO 2 in operation stage Table 1 Main specification of facilities Item Specifications Capacity Max. 21,000 m 3 /d Flocculation+sedimentation+sand-filtration Flocculation Vertical baffled channel basin flocculator Sedimentation basin Horizontal flow plate settler Sand filtration basin Self backwashing type filter Chemical feeding Intermediate chlorination: ratio (Average) 2 mg/l Post-chlorination: 1 mg/l Coagulant(PACl): 20 mg/l Activated carbon absorption Filtering type Fixed bed gravitational filtering Activated carbon Granular activated carbon Linear velocity 190 m/day Ozonation Ozone feeding ratio 2.0 mg/l Contact time 13.2 minutes Contact method Vertical baffle type flow, Diffusing pipe feeder Membrane filtration Membrane Ultra filtration (organic module membrane) Filtering type Dead end filtering Flow rate 1.7 m 3 /m 2 /day Driving method Pump pressurization -1-

2 accounts for the most part of whole energy consumption and CO 2 emission. Especially chemical feeding results in very high values. It includes those on the production of the chemicals, e.g. coagulant, chlorine. The electric power for feeding pumps, etc also causes to high LC-E and LC-CO 2 values. If the chemicals are used continuously for as long as 58 years, it is likely that a considerable load will be produced. Consequently this area offers the potential for important energy savings and reduction of CO 2 emission. LC-E (10 6 MJ/58y) Law water Flocclation Sand-filter Discharge Electricity Fig.1 LC-E for Flocculation + Sedimentation + Sand-filtration LC-CO2 (10 6 Kg-CO 2 /58y) Law water Flocclation Sand-filter Discharge Electricity Fig.2 LC-CO 2 for Flocculation + Sedimentation + Sand-filtration 2) Membrane Filtration The majority of LC-E and LC-CO 2 appear in operation stage. The result is due to electric power for pumping the raw water into the membrane. In addition, a chemical, sodium hypochlorite, for back-washing and disinfection accounts for relatively large part. This system has relatively low LC-E and LC-CO 2 amounts in construction stage. This might be due to the compact facilities of membrane filtration system. 3) Ozonation The majority of LC-E and LC-CO 2 appear in operation stage. Electric power for ozone -2-

3 generation and injection accounts for the majority of both in operation stage. This part is highly subject to energy saving according to equipments and control system required. 4) Granular activated carbon (GAC) treatment The majority of both appear in renewal stage. This is due to activated carbon which is assumed to be replaced to new one for every four years in this study. This is due to activated carbon itself. The CO 2 emission from GAC production is large because of heat processing. So it is likely that LC-CO 2 reduction in operation stage is relatively small. 5) Flocculation + Sedimentation + Ozonation + GAC + Sand-filtration An approximation was carried out on an advanced treatment system based on the previous results. The major part of LC-E and LC-CO 2 appear in operation stage. Electric power for intermediate pumps accounts for one third or a half of LC-E and LC-CO 2 amounts in the stage. It is important to consider the whole system so that the power requirement like this should be minimized. CONCLUSIONS By applying LCA to drinking water treatment it became apparent that 1) LC-E and LC-CO 2 amounts in operation stage are generally large and 2) they are mainly due to electric power for pumps and some chemicals for treatments. The important point is that the quantitative and long-term evaluation can be helpful when aiming for lasting improvements in pump operation methods and in use of consumables like chemicals, etc. In future, we expect that increasing examples of similar LCA implementation will contribute towards making water treatment system more energy efficient. -3-

4 Japan Water Research Center(JWRC) Director of Water Treatment Engineering Dept. Mr. WATARU TAKASHIMA 1 The present situation The first commitment period of Kyoto Protocol has begun since Much more efforts toward reducing environmental impacts have been required in every field of society. Water supply services also should cut the impacts in their activities. 2-4-

5 How do energy consumption and CO 2 emission depend on each drinking water treatment process and stage, i.e. construction stage, operation stage and disposal stage? Life Cycle Assessment 3 A Simple definition of LCA Life cycle assessment determines the environmental impacts of products or services, thorough production, usage, and disposal. As actual procedures, calculating Energy consumption (LC-E) or Carbon dioxide emission (LC-CO 2 ) 4-5-

6 Calculation method of LCA 1) As to one material Unit energy consumption or unit CO 2 emission Amount of materials used 2) As to all materials Summing up with all materials Easy to understand but, a lot of work 5 Calculation example(1) ー CO 2 emission per Kw of motor 1) CO 2 emission (kg-co 2 ) of 5.5KW motor (weight 116kg) in a raw material procurement stage = kg-CO 2 2) CO 2 in a production stage = 400kg-CO 2 /motor-ton 3) CO 2 a motor of 5.5kw = ( /1000) =332.1kg-CO 2 /a motor 4) CO 2 per kw = 332.1kg-CO 2 /5.5kw = 60.38kg-CO 2 /kw 6-6-

7 Calculation example(2) ー CO 2 emission of motors Installation of pumps in a construction stage 1) Unit CO 2 emission of motors : 60.38kg-CO 2 /kw 2) Power of a motor : 15 kw/unit 3)The number of motors : 2 units Total CO 2 emission in a construction stage. = kg-co 2 /kw 15 kw/unit 2 units =1,811.4 kg-co 2 7 Table 1 Main specification of facilities Capacity Max. 21,000m 3 /d Items Specs Flocculation + Sedimentation +Sand-Filtration Flocculation basin Vertical baffled channel flocculator Sedimentation basin Horizontal flow plate settler Sludge scraper Sand-filtration basin Self backwashing type Chemical feeding Intermediate Cl:2mg/l (Average) Post Cl:1mg/l PACl :20mg/l Activated carbon absorption Filtering type Fixed bed gravitational filtering Activated carbon GAC, Depth 2.4m Filter area/basin 110.8m2 Linear velocity 190m/d Items Ozonation Ozone feeding rate Contact time Contact method Number Membrane filtration Membrane module Filtering type Flow rate Driving method Specs 2.0mg/L 13.2min Vertical baffle, Diffusing pipes 2 basins Ultra filtration(organic) Dead end filtering 1.7m3/m2/d Pump pressurization Service life Buildings:58years, Pipes:38years Electric apparatus and Machine:16years 8-7-

8 Water treatment types for case studies 1) Flocculation + Sedimentation + Sand-filtration 2) Membrane Filtration 3) Ozonation 4) Granular Activated Carbon treatment 5) Advanced treatment system (Flocculation + Sedimentation + Ozonation + GAC + Sand-filtration) 9 Fig.1 Grouping of Flocculation + Sedimentation + Sand-filtration Treatment (Abstraction) Raw water Coagulant Intermediate Cl Flocculation + Sedimentation Sand-filtration Post Cl (Transmission) Discharge Washing waste water Thickening -8- (Sludge treatment) Common Electric equip. 10

9 Fig.2 LC-E for Flocculation + Sedimentation + Sand-filtration LC-E (10 6 MJ/58y) Law water Flocclation Sand-filter Discharge Electricity 11 Fig.3 LC-CO 2 for Flocculation + Sedimentation + Sand-filtration LC-CO 2 (10 6 Kg-CO 2 /58y) Law water Flocclation Sand-filter Discharge Electricity 12-9-

10 Fig.4 Details of LC-E for F+S+S-f Raw water Flocculation Sedimentatio n Sand -filtration feeding Sludge treatment Electric Receiving well Mixing basin Buffle type flocculation Horizontal-flow sedimentation basin with inclined plate settler Sand filters Feeding equipments Drainage basin Thickner Receiving & transformer Monitoring & contorl eqipments Emergency power supply Receiving well Floor pumps Mixing basin Mixers Flocculation basin Weir Sedimentation basin Inclined plate settler Scraper Discharge trough Sludge equipments Sand filters Discharge trough Filter media Collector Inlet equipments Discharge equipments washing equipments Feeding chamber Sodium hypochlorite Coagulant(PACl) Dranage basin Pumps Racks Thickner Sludge scraper Pumps Racks Receiving & transformer Monitoring equipments Insrumentation Generator LC-E (10 6 MJ/58y) Raw water Flocculation Sedimentatio n Sand -filtration feeding Sludge treatment Electric Fig. 5 Details of LC-CO 2 for F+S+S-f Receiving well Mixing basin Buffle type flocculation Horizontal-flow sedimentation basin with inclined plate settler Sand filters Feeding equipments Drainage basin Thickner Receiving & transformer Monitoring & contorl eqipments Emergency power supply Receiving well Floor pumps Mixing basin Mixers Flocculation basin Weir Sedimentation basin Inclined plate settler Scraper Discharge trough Sludge equipments Sand filters Discharge trough Filter media Collector Inlet equipments Discharge equipments washing equipments Feeding chamber Sodium hypochlorite Coagulant(PACl) Dranage basin Pumps Racks Thickner Sludge scraper Pumps Racks Receiving & transformer Monitoring equipments Insrumentation Generator LC-CO 2 (10 6 Kg-CO 2/58y)

11 Fig.6 Grouping of Membrane Filtration Treatment (Abstraction) Raw water Membrane Washing water tank (Transmission) Chemical tank Neutralization Reducing Chemical washing Chemical Waste tank Sodium hypochlorite (Sewer pipe) Discharge Common Waste water tank Thickener (Sludge treatment) Electric eqip. Coagulant Reducing agent Conditioning (Discharge) Buildings 15 LC-CO 2 (10 6 Kg-CO 2 /58y) Membrane Discharge Electricity Building

12 Fig. 8 LC-CO 2 for Ozonation LC-CO 2 (10 6 Kg-CO 2 /58y) Ozone Contact basin Feeding facilities Exhaust ozone Ozone generatorchamber Contact basin Ozon generator unit Air compressor Heat exchanger Cooling water pump Exahaust ventilation fan Instrumentation Monitoring panel Decomposing tower Catalyst Ozone generatorchamber Total 17 Fig. 9 LC-CO 2 for GAC LC-CO 2 (10 6 Kg-CO 2 /58y) Adsorption basin Adsorptionbasin Trough Avtivated carbon Filter media Collecting equipments Inlet equipments Discharge equipments Weir Washing equipments Pipes,valves Exhaust ozone facilities Incidental Facilities Building Total Notice: GAC is supposed to be renewed every four years

13 Fig.10 Grouping of Advanced Treatment (F + S +Oz +GAC +S-f) Treatment Coagulant Intermediate Cl Post Cl (Abstraction) Raw water Flocculation Sedimentation Ozone Others (Intermediate pumps) GAC Sand-filtration (Transmiss Waste water tank Common Electric eqip. Discharge Thickener (Sludge treatment) 19 Fig. 11 LC-CO 2 for F+S+Oz+GAC+S-f LC-CO 2 (10 6 Kg-CO 2 /58y) Advanced treatment Intermediate pump

14 LC-CO 2 Membrane Fil. Sand Fil Kg-CO 2 /58Years 21 Conclusion 1) LC-E and LC-CO 2 in operation stage are generally large. 2) Both of them are mainly due to electric power for pumps and some chemicals for treatments

15 Recommendations 1) Consider the electric energy saving in planning and designing. 2) Paying much attention to proper injection rate of chemicals in daily operation. As one of measures, avoiding abstracting highly turbid water would contribute to the reduction of energy and CO 2 emission. 23 Thank you for your kind attention. ありがとうございました JWRC