Life cycle asssment of wastewater treatment technologies
treating petroleum process waters
N.Vlasopoulos a,⁎,F.A.Memon c ,D.Butler c ,R.Murphy b
a
Department of Civil and Environmental Engineering,Imperial College,London SW72AZ,England,UK
b
Department of Biological Sciences,Imperial College,London SW72AZ,England,UK
c
Centre for Water Systems,School of Engineering,Computer Science and Mathematics,University of Exeter,North Park Road,Exeter EX44QF ,UK
Received 18October 2005;received in revid form 26February 2006;accepted 6March 2006
Available online 2May 2006
Abstract
This paper describes the implementation of life cycle asssment to investigate the environmental impact of 20technologies suitable for treating extensive volumes of water produced during the oil and gas extraction process.Data on the physical and operational attributes of technologies under consideration were asmbled and their life cycle environmental impacts estimated over 15year time period.The results were then incorporated in a decision support system which allows identification and prioritisation of potential technology combinations capable of producing water for nine designated industrial and agricultural end us.In total,more than 618technology combinations were investigated for their environmental impacts.The identification and prioritisation of technologies were done on the basis of their environmental and technical performance.This analysis showed that dissolved air flotation,absorbents,dual media filtration and rever osmosis technologies offer relatively low environmental impact parts of systems for cleaning such process waters.Furthermore,the environmental asssment combined within the decision support system has revealed potentially valuable indirect downstream “benefits ”from effects such as evaporative loss from wetlands in terms of the overall environmental impact of a treatment system.©2006Elvier B.V .All rights rerved.
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Keywords:Life cycle asssment;Oil process water;Produced water;Treatment technologies;Water reu
1.Introduction
Oil and gas production process generate significant volumes of contaminated process waters accounting typically for around 70%of the total volume extracted (Ekins and Vanner,2005).The waters after cleaning in some way are often referred to as ‘produced water ’and are normally either discharged to the local environment
or injected into shallow or deep aquifers.Owing to enhanced awareness of environmental issues and strin-gent discharge standards,a range of more environmen-tally nsitive options is being explored for the disposal of the waters.Potentially,the large amounts of water,if treated,could be available for veral industrial and agricultural applications.
Process water generated at oil and gas extraction facilities contains a wide variety of pollutants at varying concentrations (Menzie,1982;Chapelle,1993;Tellez et al.,2002).The pollutant nature and concentration are largely source dependent including location,geology and age of the oil and gas field.Among the
pollutants
Science of the Total Environment 367(2006)58–
70
⁎Corresponding author.Tel.:+442075946075;fax:+442075945934.
E-mail address:nikolaos.vlasopoulos@imperial.ac.uk (N.Vlasopoulos).
0048-9697/$-e front matter ©2006Elvier B.V .All rights rerved.doi:10.1016/j.scitotenv.2006.03.007
found in the process waters requiring treatment include oil and grea,boron,total dissolved solids(TDS)and sodium.A typical concentration of the pollutants found in oil and gas extraction process waters is shown in Table1.
Decision on lecting appropriate treatment technol-ogies(and their combination)capable of achieving a desired end u quality not only requires performance data but also asssment within an economic and envi-ronmental sustainability context.Several authors have ud life cycle asssment(LCA)methodology to esti-mate the environmental loads from wastewater systems (Emmerson et al.,1995;Dennison et al.,1998;Mels et al.,1999;Lundin et al.,2000;Dixon et al.,2003).The majority of LCA studies have compared different con-ventional treatment methods(Emmerson et al.,1995; Dixon et al.,2003)or management scenarios(Dennison et al.,1998;Mels et al.,1999),while others assd the influence of system boundaries and scale on ca
lculated environmental loads(Lundin et al.,2000).However, none of this LCA studies concentrated on treating pe-troleum process waters.
This paper deals with the investigation of environ-mental implications of veral potential produced water cleaning technologies.The environmental attributes/im-pacts quantified for each of the technologies have been incorporated into a decision support system developed at Imperial College(Dillon,2003).The extended new version of the decision support system facilitates de-cision making using holistic approach by considering environmental impacts and economic implications.公务员礼仪培训
The basis for this study is on the cleaning of a volume (10,000m3per day)of process water to give a final volume of cleaned water at appropriate water quality levels for a variety of end us.The‘functional unit’for the LCA in this study therefore differs somewhat from more common product-orientated LCAs in which em-phasis is placed on a more rigid end-point of function provided by,typically,a manufactured product or ma-terial.Here the emphasis is placed on a functional unit reprentative of a‘rvice’provision(that of cleaning process water)where the main objective is to achieve a satisfactory onward provision of water at a quality ac-ceptable to potential markets.The amount of cleaned water output achieved by various technology combina-tions in this study is therefore not of significance but the input of produced water is.For example,in the prent study the
evaporative loss of water from the managed wetland system are assumed to be 40%of the input volume)but this does not affect the analysis since the system still receives the same functional unit input as the other technologies evaluated.
The environmental impacts of different water clean-ing technologies are evaluated both individually and as systems or‘trains’of technologies capable of achieving desired water quality outputs.
2.Materials and methods
2.1.Treatment technologies
Process water from refineries and oil producing wells can be treated in a number of different ways(Galil and Rebhun,1990;Alther,1995;Husley et al.,1995; Cheryan and Rajagopalan,1998;Knight et al.,1999; Andreozzi et al.,2000;Al-Shamrani et al.,2002;Tellez et al.,2002).Dillon(2003)reviewed and evaluated the potential of veral technologies to treat the petroleum containing process water(Table2).The available technologies can be grouped into4different treatment
appetiteTable1
Typical process water quality parameters(Dillon,2003)
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Parameters Value(mg/l)俄语字母表
Oil and grea200
Boron5
Total dissolved solids(TDS)5000
Sodium2100
Table2
Categorisation of treatment technologies(Dillon,2003)
Stage1Stage2Stage3Stage4Additional
jhj
Dissolved air flotation (DAF)Rotating biological
contactors(RBC)
Dual media filtration
(DMF)
Rever osmosis
(RO)
Ion exchange
(ION)
Hydrocyclones (HYDRO)Absorbents
(ABS)
Granular activated carbon
(GAC)
Electrodialysis reversal
(EDR)
Activated sludge(AS)Slow sand filtration(SSF)
Trickling filters(TF)Ozone(OZO)
Air stripping(AIR)Organoclay(ORG)
Aerated lagoons(AL)Ultrafiltration(UF)
Wetlands(CWL)Nanofiltration(NF)
Microfiltration(MF)
59 N.Vlasopoulos et al./Science of the Total Environment367(2006)58–70
stages depending on their ability to treat the oily waste-water as well as on their requirements regarding the influent water quality.
•Stage1:Technologies in this stage typically include hydrocyclones and dissolved air flotation and are aimed at significantly removing oil and grea to levels acceptable to downstream treatment stages.•Stage2:Technologies in this stage include biological process,such as trickling filters or acti
vated sludge, or physical treatment,such as air stripping or absor-bents are employed to further reduce oil and grea concentration to levels suitable for disposal or further treatment.
•Stage3:This stage employs technologies that require good influent water quality for their smooth and economic operation.This stage typically includes activated carbon or organoclay technologies as well as membrane technologies,such as ultrafiltration or nanofiltration,to further reduce the oil and grea concentration to levels suitable for Stage4of treatment.
•Stage4:Technologies in this stage typically include electrodialysis reversal(EDR)and rever osmosis(RO)and are ud to remove dissolved pollutants such as sodium,total dissolved solids and boron in order to produce high quality water for reu.
A‘treatment system’or treatment train normally consisted of one option from each of the four stages.In this way,more than600different systems were ge-nerated and investigated.A few additional treatment systems were also investigated by employing micro-filtration(MF)as combined Stage1and Stage2techno-logy.This investigation of MF was limited due to the uncertainty surrounding its performance and effective application(Zaidi et al.,1992;Bilstad and Espedal, 1996).Stage1to3technologies are ud to reduce the oil and grea to levels that can be either disch
arged or reud.The fourth stage of treatment is ud to reduce the sodium,TDS and boron levels to produce high quality water required by some end us.In addition when required for certain us,ion exchange(ION)was added at the end of the treatment system to further remove pollutants such as boron.
The technology combinations were lected in order to achieve the target water qualities for the nine end us shown in Table3(Dillon,2003).
2.2.LCA methodology
The life cycle impact asssment of the technologies (and their combinations)was carried out bad on the ISO14040ries of standards.SimaPro6(Pre Consultants BV)was ud for the LCA modelling. 2.2.1.Goal and scope
The primary goal of the rearch was to evaluate the environmental impact of the treatment technologies and their combinations that are capable of producing water quality required for the end us in Table3.It was assumed that the facilities needed for each technology are a conventional factory where the process water treatment is the“product”and the resources,energy u and possible wastes are the inputs and outputs coming in or out respectively from this factory in order to produce t
he desired“product”.
2.2.2.Functional unit
The functional unit is a measure of the performance of the product system.The primary purpo of the functional unit is to provide a reference to which the inputs and outputs are related and is necessary to ensure comparability of results.
A process water flow of10,000m3/day for a time period of15years(system design life)was ud in the prent study in order to compare the different wastewater treatment process.It is estimated that the uful life of a typical treatment works,regardless of structural type,is limited to an average of fifteen years (Emmerson et al.,1995).This is partly due to developments in available technologies and increas in the amount of produced water treated as the oil/gasorphans
Table3
Typical quality requirements for nine different end us
Agricultural u Industrial u
Barley Alfalfa Wheat Sorghum Cotton Rhodes Citrus Cooling system feed Boiler feed Boron(mg/l)160.655660.51010 Sodium(mg/l)20025020025050050015025001000 TDS(mg/l)500025005000300070006000120055002200
Oil(mg/l)111111111
60N.Vlasopoulos et al./Science of the Total Environment367(2006)58–70
formation matures.However,when the design life of a particular technology was estimated as shorter than 15years (brane technologies),the environmental cost for replacement parts was included in the analysis.The available data for the materials and energy needed for the various process wastewater treatment technologies have therefore been referenced to a total of 54,750,000m 3of process water treated over a 15year period.
2.2.
3.System boundaries
throatThe system boundaries determine which unit pro-cess shall be included within the LCA.Two different configurations of the product system were considered in this study.The first one examines th
e environmental aspects of the different technologies that are employed in each stage,as well as the environmental performance of the combined Stage 1and Stage 2technologies compared with MF.The cond configuration examines the envi-ronmental aspects of different stage wi technology combinations as given in Table 2.The system boundaries for the two configurations are shown in Figs.1and 2.All the process in grey-shadowed boxes are included in the analysis.The solid arrows in Figs.1and 2illustrate the possible technological quences that can be employed.The corrugated plate interceptor (CPI)unit at the head of
the system is not included in the system,since it is suppod to be the same for all the scenarios in both configurations.The primary function of CPI is to remove the bulk of the oil and suspended solids.
For the first configuration,technologies falling with-in each stage (enclod by a dashed rectangle)were treated as individual entities and their environmental impact was investigated parately.For the cond con-figuration a full treatment train (consisting one technol-ogy from each stage)was examined in an overall analysis.Five scenarios were investigated in the cond configuration (enclod by various dashed rectangles)and were combinations capable of providing water that could meet at least one end u requirement in Table 3.Technology combinations of Stage
1and Stage 2only were not examined since they do not produce water of sufficient quality required for any nine end us considered.The scenarios examined were:•Scenario 1:Stage 1+Stage 2+Stage 3•Scenario 2:MF +Stage 3+Stage 4
•Scenario 3:MF +Stage 3+Stage 4+ION
•Scenario 4:Stage 1+Stage 2+Stage 3+Stage 4•
Scenario5:Stage 1+Stage 2+Stage 3+Stage 4+ION
For each of the technologies (or technology combina-tions),the LCA considered their impact during
the
Fig.1.Process line —System boundaries of the 1st
configuration.
Fig.2.Process line —System boundaries of the 2nd configuration (CPI:corrugated plate interceptor,MF:microfiltration,ION:ion exchange).
61
N.Vlasopoulos et al./Science of the Total Environment 367(2006)58–70
construction aterials required to build the facility)and the operation(u)pha(materials and energy required during the facility operation).The system was modelled independently of a specific geo-graphic location so transport of materials to a specific site was excluded.Downstream impact of the reu activities of the produced water,the disposal of wastes arising from the chon treatment sludges)and the eventual facility decommissioning were also exclud-ed from the system boundary since they can vary greatly depending upon local conditions and regulations.
2.2.4.Life cycle inventory analysis
Inventory data for the construction and the u pha of each of the20technologies was collected by ques-tionnaire contact to over160equipment designers,ma-nufacturers and suppliers.The inventory analysis was simplified by considering only primary inputs of energy and materials,as previous studi
es have demonstrated that condary effects,such as construction of manufacturing plants and manufacture of vehicles,typically account for less than5%of the total impact(Hunt,1991).Waste production during the u pha differs between the various technologies considered.Table4summaris the quantity and quality of the waste streams,as well as the available methods for their treatment/disposal(Dillon, 2003;Vlasopoulos,2004).It is apparent that the quantity and quality of the produced waste streams by each technology differ significantly,and according to the lected treatment/disposal scenario will lead to different environmental impacts.The energy consumed by each technology is assumed to be generated by the Union for the Coordination of Production and Transmission of Electricity(UCPTE)energy mix(energy mix of23 European countries including France,Germany,Italy etc.),which consists of the following energy sources:(1) coal17.4%,(2)gas7.4%,(3)hydropower16.4%,(4) lignite7.8%,(5)uranium40.3%and(6)oil10.7% (derived from SimaPro databa).Further details on the methodology and the approach ud for preparing the inventories for different technologies are available in Vlasopoulos(2004).
2.3.Life cycle impact asssment(LCIA)
The development of life cycle inventories and sub-quent asssment and interpretation of the inve
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ntory data was carried out using SimaPro(Version6).The LCIA was conducted using the CML2baline2000 v2.1(Goedkoop et al.,2004)impact asssment method.Normalization of the impact category indicator results was done using the Western Europe1995criteria. It is expected that each technology will produce water of various quantity and quality.However,no value was
Table4
Quantity,quality and possible treatment/disposal methods of waste streams produced during the u pha of the treatment technologies Technology Waste streams of treatment technologies during u pha
Quantity Quality Treatment/disposal methods
DAF220m3/d Mixed sludge of oil and coagulant Oil and coagulant recovery/
Incineration/Landfill
HYDRO50m3/d Oily sludge Oil recovery/Incineration/Landfill
ABS40kg/d Spent woolspill Recycling/Incineration/Landfill
AS850m3/d Microbiological sludge Anaerobic digestion/Land application/Landfill AL800m3/d Sludge undergoes aerobic and anaerobic digestion Composting/Land application/Landfill
AIR50kg/d Spent carbon,ud to treat the vapour pha Incineration/Landfill
MF230m3/d Oily sludge Oil recovery/Incineration/Landfill
marry you歌词RBC200m3/d Microbiological sludge Anaerobic digestion/Land application/Landfill TF370m3/d Microbiological sludge Anaerobic digestion/Land application/Landfill CWL0No sludge produced
DMF200m3/d Backwash sludge Land application/Landfill
GAC50kg/d Spent carbon Incineration/Landfill
NF800m3/d Mixture of oil,sodium,TDS and Chemicals ud
for fouling prevention
Landfill
ORG95kg/d Spent organoclay Incineration/Landfill
OZO0.5kg/d Spent zeolite from oxygen gas generator Landfill
SSF40m3/d Skimming of and washing of top sand layer Land application/Landfill
UF285m3/d Backwash sludge with NaOCl Landfill
EDR2500m3/d Brine Evaporation ponds/Deep well injection
RO2000m3/d Brine Evaporation ponds/Deep well injection
ION25m3/d Sludge containing hydrochloric acid,sulphuric acid,
sodium chloride,sodium sulphate and boron Landfill
62N.Vlasopoulos et al./Science of the Total Environment367(2006)58–70
