Desalination 357 (2015) 45–54

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Desalination

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Comparative life cycle assessment of end-of-life options for reverseosmosis membranes

Will Lawler a, Juan Alvarez-Gaitan b, Greg Leslie a, Pierre Le-Clech a,⁎a UNESCO Centre for Membrane Science and Technology, School of Chemical Engineering, The University of New South Wales, Sydney, NSW, Australiab Sustainability Assessment Program, Water Research Centre, The University of New South Wales, NSW, Australia

H I G H L I G H T S

• Life cycle assessment model for RO membrane manufacturing and end-of-life options• Impact put into the context of total emissions from potable water production• Membrane reuse over one year is more environmentally favourable than landfill.• Transportation distance and lifespan play a significant role in reuse viability.• Provides quantitative information for end-of-life decision making

⁎ Corresponding author.E-mail address: p.le-clech@unsw.edu.au (P. Le-Clech).

http://dx.doi.org/10.1016/j.desal.2014.10.0130011-9164/© 2014 Elsevier B.V. All rights reserved.

a b s t r a c t

a r t i c l e i n f o

Article history:Received 7 August 2014Received in revised form 3 October 2014Accepted 8 October 2014Available online xxxx

Keywords:Life cycle assessmentReverse osmosisDesalinationManufacturingReuseRecycling

With continuing growth in the reverse osmosis water treatment industry and the finite lifespan of themembranes, the number of membrane modules requiring disposal is expected to drastically increase overtime. This study aimed to provide a quantitative assessment of the environmental impact from membranemanufacturing and its impact on the desalination process, using the tool of life cycle assessment. The resultsshowedno significant difference between themanufacturing of 16″ and 8″ elements, and thatmodule fabricationcontributed to less than 1% of the CO2-e emissions for the production of potable water from seawater. The studyalso looked at the environmental impact of a number of proposed end-of-life disposal options for membraneswithin the context of the Australian desalination industry. The results of the study show that membrane reuseover one year is more environmentally favourable to landfill disposal, regardless of the transportation distancerequired. However, in terms of direct reduction of waste to landfill, incineration provided the greatest benefit,at the expense of increased greenhouse gas emissions. Overall, this study provides detailed quantitativeinformation for membrane users and manufacturers to enhance their decision making process when it comesto end-of-life membrane options.

© 2014 Elsevier B.V. All rights reserved.

1. Introduction

Over the last few decades, the use of desalination technologies hasdramatically increased and a large proportion of this has been mem-brane based plants. In Australia, the size and number of these plantshave also increased, with large scale plants being located around thecountry. Australia has six big municipal seawater desalination plants,plus over a hundred commercial plants of varying sizes [1].

An average of one hundred 8″ reverse osmosis (RO) modules, whichweigh between 13 and 15 kg and have an average lifespan of 5–8 years[2,3], are needed to produce 1000 m3/day of product water. It has been

estimated that the mass of disposed membranes in Australia alone isexpected to reach 800 tonnes/year by 2015 [4]. Currently, once an ROmembrane reaches the end of its life, it is disposed in local municipallandfills. Increasing awareness of the environmental impact of prod-ucts and processes has led to the development of environmentalmanagement tools to better understand and manage these effects. Lifecycle assessment (LCA) is a systematic tool for assessing potential envi-ronmental consequences andhas been increasingly applied to thewater[5,6], wastewater [7] and membrane industries [8–10].

A number of LCA studies have been conducted on various watertreatment processes, including desalination with RO [11]. The majorityof these studies focus on the operation phase of the process, includingchemical and energy requirements, as they have been shown to havean overwhelmingmajority of the contribution to environmental impact[12,13]. However, a number of these studies have briefly explored the

46 W. Lawler et al. / Desalination 357 (2015) 45–54

impact of ROmembrane production and renewal, showing that it gener-ally contributes less than 5% to the overall environmental impact of theprocess [14,15]. However, these studies have not adequately assessedthe impact of membrane manufacturing or explored possible end-of-life disposal options for used membranes.

This study provides a novel perspective on the specific disposalchallenges of the RO industry to help increase its environmentalsustainability. Firstly, this study aims to complete the first processbased life cyclemodel of the production and transportation of ROmem-branes, including all stages of membrane casting and module assembly.This model will be used to assess the impact of membrane manufactur-ing and transportation in the larger context of seawater desalination,and to compare the impact of using 8″ or 16″ elements. Secondly, itassesses a variety of end-of-life disposal options, addressing the specificchallenges in Australia including transportation distances and industryregulations. The effect of variation in membrane reuse lifetime and re-quired transportation distance will be explored through a sensitivityanalysis and the mass sent to landfill will be calculated for each end-of-life option.

2. Methodology

This LCA study follows the ISO 14040-44 guidelines [16,17], andcomprises of the four major steps of, goal and scope definitions, lifecycle inventory (LCI), life cycle impact assessment (LCIA), and interpre-tation. Scenario models were developed for membrane manufacturingand available end-of-life options. These models were generated andassessed using Simapro version 8 software and the Ecoinvent 3 andAusLCI databases.

2.1. Goal and scope definition

This LCA study was undertaken to assist in the decision makingprocess to determine the most preferable disposal options, drivingmembrane users and manufacturers to more sustainable practices.The intended audience of this study is a combination of policy makers,membrane experts, manufacturers and users. The study aims to answerthe question: “Which end-of-lifewaste treatment option is best for usedROmembranes fromAustralianmunicipal seawater desalination plants,from an environmental, and resource consumption point of view?”

Era

Use andMaintenance

Reuse andrecycling

Disposal

Recycling

Reuse

Production

End-of-life

Use

Fig. 1.Membrane life cycle. (For interpretation of the references to colour

In addition to the general goal, special consideration is given to:

- The impact and significance of membrane manufacturing,- The sensitivity to transportation distance and secondary life span,- Diversion of waste from landfill.

Fig. 1 shows a representation of a standard membrane lifecyclefrom extraction of raw materials to various end-of-life options.This study is focused on the disposal options, highlighted in green,and the impact of the different options is assessed on a comparativebasis. To truly understand the benefits of the various options and toput the waste issue into context, a detailed model of membraneproduction (highlighted in orange), has also been completed. Thismodel of membrane production includes the extraction of raw ma-terials and manufacturing, packaging and distribution of the mod-ule. Therefore, the only component not considered in this study isthe “use” phase of the membrane. This is contrary to nearly everyprevious LCA study on membrane water treatment, as they havemostly focused on the use phase. The use phase is not consideredin this study as it is assumed that all membranes are equivalentafter reaching the end of their life and that the energy and materialconsumption during their life span does not affect the impacts fromthe disposal options.

The LCA boundaries define what is included within the model forall processes considered. The membrane systems under discussionfor this study are being used in desalination plants located inAustralia's major cities, i.e. Sydney, Melbourne, Adelaide and Perth.The membranes used are assumed to be manufactured in theUnited States (US) of America, transported to Australia, then used,recycled and disposed of locally. As the membrane constructionand use phases occur in different geographical locations, respectivelocal data has been used. For example, values used for membraneproduction modelling were obtained from US sources, while end-of-life options were based on Australian information. The bound-aries of these models include all inputs and emissions associatedwith the contained processes (processing, manufacturing, transpor-tation etc.), and with the infrastructure required (machinery, build-ings, vehicles etc.). Due to the geographically spare nature of thevarious end-of-life options, a thorough transportation model is alsoincluded.

xtraction ofw materials

Design andProduction

Packagingand

Distribution

in this figure, the reader is referred to the web version of this article.)

Table 1Composition of dry 8″ and 16″ SWRO membrane elements.

Component 8″ element mass of material (kg) 16″ element mass of material (kg) Type of material

Outer casing 1.83 6 Fibreglass with polyester resinMembrane sheet 4.63 19.7 Polyester (PET) base with polysulfone (PSf)

supporting layer and polyamide (PA) active layerFeed spacer 1.45 6.16 Polypropylene (PP)Permeate spacer 1.81 7.6 Polyester (PET)Tube and end caps 2.38 7 Acrylonitrile butadiene styrene (ABS)Glued parts 1.37 5.2 Polyurethane glue

47W. Lawler et al. / Desalination 357 (2015) 45–54

2.2. Functional unit

The functional unit that is used for this study is one 8″ standard thinfilm composite (TFC) RO membrane module, specifically a FT-30 typewith a polyamide (PA) active layer, polysulfone (PSf) support layer,and polyester (PET) base. The exact material breakdown of the elementmodelled in this study is summarised in Table 1. The 8″ module isapproximately 1 m in length and 20 cm in diameter, with an averagedry weight of 13.5 kg and a drained weight of 15 kg. This module wasselected due to its state-of-the-art technology and current wide spreaduse [18]. To compare the standard element size to the larger 16″ alterna-tive, the functional unit of membrane surface area (m2) is used.

2.3. Life cycle inventory and impact assessment

As this study includes a wide number of waste treatment options,some which are available in Australia, consistency and quality of dataare primary challenges. Where possible, primary data has been collect-ed from known industrial processes. Extensive experimental data hasbeen generated specifically for this study's umbrella project, which in-vestigates practical alternative reuse, recycling and disposal optionsfor used ROmembranes [19,20]. This data includes, membranematerialcomposition, material thermal properties, membrane manufacturingtechniques, and membrane cleaning, storage and chemical conversionmethods. All known direct and indirect emissions, for processes withinthe system boundary, have been included in the scenario models.Where direct data collectionwas not possible, information fromperson-al communication with membrane manufacturers and companiesutilising the waste scenario has been used. Finally, where no otherdata source has been identified, literature data has been utilised. Tocomplement the collected information, this study utilises the Ecoinvent3 database and the AusCI database to provide locally relevant data.

To help with the interpretation of the LCA model and thus thecomparison of the different disposal scenarios, the ReCiPe midpointhierarchist life cycle impact assessment (LCIA) has been used [21].This method has been selected due to its relevance to the study type,recent development, and compatibility with data sets used. It is aproblem-orientedmidpoint approach, meaning that the impact catego-ry indicators are directly derived from the inventory results. While nineimpact categories from the ReCiPemethodwere chosen and assessed inthis study, climate change potential and fossil fuel depletion wereselected for further discussion, as they are easily interpretable, havelow data uncertainty and are globally relevant [21,22]. Detailed inputand output tables can be found in the supporting information.

To assess the quality of the model and data used, an uncertaintyanalysis was completed for membrane manufacturing and all end-of-life scenarios. Data uncertainty built in to the database was used, orwas calculated from experimental standard deviation, min/max values,or estimated geometric standard deviation using a pedigreematrix [23].The uncertainty calculationswere completed usingMonte Carlo simula-tion through the Simapro software using 1000 runs and confidenceinterval of 95%. Pairwise comparisonswere used to assess the differencebetween all the end-of-life scenarios [24].

3. Model description

3.1. Membrane manufacturing

In order to determine the significance of various end-of-life optionsfor used RO membranes, particularly the reuse scenarios, a detailedmodel of themembrane manufacturing is required. This manufacturingmodel can also provide additional insight into the impact of useddifferent membrane types and configurations, and their contributionto the entire water treatment process.

The manufacturing and use phase of Fig. 2 shows how the construc-tion of the module is broken up into a number of components. Whilethe exact composition of the membranes can vary from type and man-ufacturer, average values are generated from numerous membraneautopsies and manufacturer information [25,26].

The manufacturing of the various plastic components includingthe permeate tube, spacers and end caps, uses commonmoulding tech-niques. Each partwasmodelled individuallywith respect to their specif-ic moulding style and the materials involved. The membrane sheetscomprise of 37 m2 of a three-layer membrane constructed of varyingpolymers. By weight, the most significant layer is the spun-bondedpolyethylene terephthalate (PET) support layer, which provides thestructural foundation for the remaining two layers. Information from avariety of manufacturers has been adapted for this support layer[27–29]. The second layer of the RO membrane is constructed of PSfvia phase inversion. This model was constructed from the Ecoinventdata using stoichiometric calculations of the base chemical componentsin addition to estimated energy and water inputs [30]. A numberof different solvents can be used for the casting phase; however,dimethylformamide (DMF) is used in this model as it is themostwidelyreported [31,32]. The process consumes 4 kg of DMF for every 1 kg ofmembrane produced, assuming a 20 wt.% polymer mix and no solventrecovery [32]. The final membrane layer is constructed of dense PAand is laid on the PSf via interfacial polymerisation. RO membranes ofFT-30 construction are aromatic with a highly crosslinked structure,and are based on the reaction of m-phenylenediamine (MPD) andtrimesoyl chloride (TMC). This layer is around 0.02 μm thick, andthus only 30 g of the polymer is found in each membrane module. Asno specific data on the chemical components of the PA used for ROmanufacturing, and due to the relatively small amount in use, inputsfor Nylon 6.6 (an aliphatic PA) have been used in its place. The totalmembrane sheet production process includes two casting and curingphases [33].Water, which is used in both casting stages for precipitationand washing, is estimated based on available literature and existingknowledge on membrane casting to be recirculated at a rate of 20 Lpermodule [31,34]. Energy use from the heating andmachine operationhas been estimated based on Ecoinvent data on similar materialmanufacturing.

The membrane module is assembled by glueing of the membranesheets to the permeate tube, with layering of the feed and permeatespacers, and then rolled up and glued into place. The endcaps are fittedonto the permeate tube and the fibreglass case is cast around themem-branemodule. Energy consumption and production time of this processhave been based on personal communications with membrane

Membrane manufacturing

Transport

Transport

Transport

Transport

Landfill

Incinera onShredding Electricity produc on

Gasifica on Syngasscombus onDisassembly Shredding Electricity

produc on

WashingDisassembly Crushing Electric ArcFurnace

Cokeproduc on

DisassemblyShredding

andcleaning

MaterialRecycling

Offset material

produc on

Compac on Conversion Reuse asUF module

Direct Reuse

Membrane manufacturing

Membrane manufacturing

Sor ng

Cleaning

Packagingand

storage

Packagingand

storage

Manufacturing and use phase End-of-life processing Process offsets

UsedMembraneTransport

Packaging

Fibre glasscase

End caps

Membrane sheets

Spacers

Permeate tube Granularplas c

Extrusionmoulding

Granularplas c

ExtrusionSpunbonding

Support layermanufacturing

Membrane layer cas ng

Granularplas c

Extrusionmoulding

Resin and glassstrand

extrusion

Filamentwindingmouling

Storage solu on

Plas c bag andcardboard box

Fig. 2. Simplified process flow diagram for membrane manufacturing and end-of-life scenarios including offsets.

48 W. Lawler et al. / Desalination 357 (2015) 45–54

manufacturers andmodule rollingmachines. Thefinal component of themembrane element is theO-ring that is fitted around the feed side of themodule, it is made out of ethylene propylene rubber and weighs 30 g.

3.2. Disposal options

3.2.1. LandfillLandfill involves the disposal of waste by burial and is the most

commonmethod utilised in Australia [35], and is therefore the baselinescenario for comparison. Due to their mostly polymeric composition,membranes are considered inert municipal solid waste in the case oflandfill disposal. The inert components are not toxic and thus themain problem associated with their existence in the landfill is due toland occupation and transportation [36].

3.2.2. IncinerationIncineration is a thermal waste treatment method that involves the

combustion of materials to produce ash, gas emissions and heat, whilereducing the volume of the waste material. Incinerators generallyoperate at above 850 °C and combustion occurs in an excess of oxygen[37]. Plastic waste is considered a good fuel source because they havea heating value almost equivalent to that of the coal. The thermal energyproduced from the waste incineration is used to generate electricalenergy, which is the primary offset of this scenario. Additionally, therecovered energy can reduce pressure on existing generation facilities.Incineration also greatly reduces the volume of waste by about 90–95% [38]. While incineration is commonly used in countries with strictland use requirements [39], and in some cases has been shown to beenvironmentally favourable to landfill [40,41], current Australianregulation states that incineration cannot be used for municipal solidwastes [42]. Therefore, due to lack of local information, this modeluses international literature data, coupled with bench scale experimen-tal work [43].

3.2.3. Syngas productionGasification is the partial oxidation of carbon-based feedstock to

generate syngas, which is directly combusted onsite in an internal

combustion engine generator to produce electricity [44]. Oxygen isadded to maintain a reducing atmosphere, but the quantity is main-tained lower than the stoichiometric ratio for complete combustion.The major input and emissions data for this scenario has been adaptedfrom a detailed survey of gasification facilities using plastic feed compo-nents in North America [45,46], with information on membrane collec-tion, disassembly and sorting added to complete the model.

3.2.4. Energy recovery in EAF steelmakingAnother possible option is the use of the polymeric membrane com-

ponents as a substitute carbon source in an electric arc furnace (EAF)steel making process. The use of waste plastics and rubbers as a substi-tute or metallurgical coke has been extensively tested in recent yearsand has seen commercial use [47]. This method has been specificallytestedwithmembrane components and the results show a similar ben-efit of their use, when compared to other waste materials [19]. A partialwaste polymeric material substitute actually improves the processthough increased energy retainment and promotion of foamy slag. Anumber of detailed LCA studies on polymeric substitution have shownan insignificant change in flue gas emissions, and highlighted that theprimary benefit from using this technique is the diversion of polymericmaterials from landfill, and the reduction in coke consumption [48,49].The process requires the removal of the membrane case, as its silicacomposition is unsuitable for EAF applications and rigorous plasticwashing to remove contaminates is also required. While substitutionrates between 1–1.7 kg of polymer to kg of coke have been reported[50,51], a 1 kg/kg rate using a mixture ratio of 30:70 polymer to cokehas been selected for this study, as this was the composition specificallyassessed during bench scale testing [19].

3.2.5. Material recyclingThe primary recycling method for end-of-life plastic components is

mechanical recycling [52], which involves the shredded plastic flakesbeing melted and reformed via melt-extrusion, to produce uniformly-sized pellets which can be used as a raw material for new products[53]. This process required the module to be disassembled and sortedprior to the plasticwashing and grinding stages. Due to the requirements

49W. Lawler et al. / Desalination 357 (2015) 45–54

of mechanical recycling, only the ABS components, including the tubeand end caps, and the spacers are suitable for this method, with allother components being sent to landfill [54,55]. Following the sortingand shredding phase (were 5% material loss is assumed), the materialgoes through the process of melt-extrusion, and it is assumed thatthere is a 10% loss of material and product quality [56]. The benefitof this process is realised through the production offset of virginplastics.

3.2.6. Direct RO reuse and conversion to UF membranesDirect membrane reuse involves taking membranes that have been

deemed unsuitable for their primary application from one plant andtransporting them to a secondary plant. The most viable secondary ap-plication involves harsh feed water conditions that require regularmembrane replacement. As the functional unit of this study is one ROmembrane, it is assumed that the module is suitable for direct reuse.To estimate the potential lifespan of the membrane during its seconduse, a survey of membrane conditions from companies facilitatingmembrane reuse has been used [57]. Using this data, manufacturerspecifications and expected membrane lifetime, it was estimated thata membrane reused in harsh brackish water RO conditions wouldhave a virgin membrane production offset of 33%, followed by disposalin landfill. While the membrane reuse will offset production, it alsorequires an additional cleaning, packaging and preservation step priorto transport. These have been modelled on industrial best practice andincorporated into this scenario [58,59].

If the membranes are not suitable for direct reuse as RO, they can beconverted with chemical treatment to UF. This technique exploits therelative vulnerability of the PA layer to oxidative chemicals to removeit, leaving the PSf layer intact, which can act as a UFmembrane. The de-tails of the process, which this model is based on, have been extensivelystudied and previously published [20]. This model used the applicationof UF pre-treatment for RO systems and assumes that the lifetime of thereusedmembrane is 2 years. As themembranes only have a finite reuselifespan, these options are only a form of lifecycle extension, rather thana true end-of-life scenario. Therefore, in this model, the membranes aredisposed of in landfill, following their reuse lifespan.

Fig. 3. Relative impact from different components during the manufacturing of one

3.2.7. TransportationAnumber of studies have shown that the exclusionof a detailed trans-

portation model in an LCA study can result in a severe underestimationof the environmental impacts of disposal scenarios [60,61]. This is par-ticularly important in this study as each scenario has a different corre-sponding transportation distance and method, and due to Australia'ssize and sparsity. The details of the transportation model can be foundin Table S2 of the supporting information. The distances to landfill andprocessing sites were calculated from surveys of available locations.

4. Results and discussion

4.1. Membrane manufacturing

A detailed model of the impacts from the manufacturing processesof RO membranes is vital for understanding the effectiveness of thestudied reuse, recycling and disposal options. In the situation that onlylandfill, recycling and incineration are considered, a model includingonly the material components may prove suitable. However, as thisstudy includes a number of scenarios that rely on the offset of mem-brane production itself, a detailed model with the energy required forproduction and the consumables like solvents and water is vital for get-ting a clear picture of the viability of the various scenarios. Fig. 3 showsthe contribution of the different components to the total environmentalimpact of the membrane manufacturing process. This type of represen-tation is useful for determining which parts of the manufacturingprocess have the most significant impact, and thus identifying area ofpossible improvement.

The relative environmental burden for 9 difference impact catego-ries relevant to this study is displayed, and can be used in conjunctionwith the absolute values to provide detailed context for the emissions.In terms of climate change potential for the module manufacturing,the results show that, overall, the production and transportation of an8″ RO element contribute 87 kg CO2-e emissions to the atmosphere.The largest contributor for this impact is from the membrane sheetmanufacturing; with this being the heaviest component within themodule (Table 1). With 4.63 kg of membrane sheets required for each

RO module. Values above bars are the total emissions for the impact category.

50 W. Lawler et al. / Desalination 357 (2015) 45–54

module, they make up 45% of the total CO2-e emissions, with 25%originating from the support layer manufacturing and 12% comingfrom the solvents used in the PSf and PA layers. Interestingly, despitethe vast distances associated with the transportation of the membranefrom its manufacturing location in the United States to the point ofuse in Australia, it only contributes to 8% of the total climate change im-pact. Interestingly, the marine eutrophication emissions are dominatedby the production of the PSf and PA layer with the solvents required(particularly the N,N-dimethylformamide used for the PSf production)having 90% of the contribution, due to the volumes of nitrogen thattheir production releases into the environment. Finally, the resultsshow that the production of a 13.5 kg membrane element requires theconsumptions of 38.5 kg oil-e.

Uncertainty analysis shows that climate change and fossil fuel deple-tion have the lowest uncertainty of all the impact categories, with anoverall variation between 11 and 13%. This is acceptably low, when itis considered that the model comprises of over 10,000 values, eachwith an associated uncertainty. The uncertainty for the other impactcategories varies, with the highest values obtained fromhuman toxicity,marine eutrophication and ecotoxicity. This trend is due to the qualityof the data, compounding uncertainties of the numerous layers inthe model, and the limited knowledge of the impact of the variouscompounds on the environment.

4.2. Impact of membrane module size on production emissions

There is increasing interest in the desalination industry in the largerstandard format of 16″ elements. These modules are constructed out ofsimilarmaterials to the 8″ elements but can be over 60 kg in weight andhave 4 times the membrane surface area. To compare the environmen-tal impact of the two formats, the 8″manufacturingmodel was adaptedfor the 16″ elements, including changes in associated production inputsand transportation requirements. The results show that the productionof the larger module is associated with 348 kg of CO2-e, while theequivalent 4 8″ modules results in 351 kg of CO2-e. While there issome variation in the other impact categories, the results do not showa significant difference between the two. This suggests that there is nobenefit to be gained from manufacturing a smaller number of largermodules. However, this analysis does not take into account the potentialreduction of plant equipment and maintenance which are part of theadvertised benefits of the larger format. Therefore, this LCA modelcannot conclusively show that there is benefit from using the largerelements and further information about the variations in membranemanufacturing is required to make a more detailed and conclusiveassessment.

4.3. Contribution of RO manufacturing to desalination operation emissions

While any reduction in process waste can help the industry becomemore environmentally friendly, it is important to put the impact ofmembranemanufacturing and replacement into context. For a consum-able component, such as a RO membrane, it is logical to compare itsimpact relative to the overall process. A number of LCA studies of vary-ing depths and qualities have been completed on seawater desalination,with themajority focusing on the energy consumption,which is consid-ered to be relatively high for RO processes [3,11,62]. This focus onenergy generally means that infrastructure and consumables are eitherignored, or simplified.

In order to put membrane production impacts into context with theentire RO process, without performing a detailed LCA of RO watertreatment, the obtained values can be compared to literature data. Sur-prisingly, out of all the studies reviewed, only four included absoluteemission values (primarily kg CO2-e). A fifth study by Plappally et al.,provided a review of energy consumptions for RO processes aroundthe globe and was thus consider significant enough to include by

using Simapro and the AusLCI database to estimate the emissions [62].Details can be found in Table S3 of the supporting information.

Assuming that one membrane produces on average 10 m3/day, andan average lifespan of 7.5 years, 27,400 m3 of water are produced in itslifespan. Additionally, the production, transportation and subsequentdisposal of one membrane module are associated with the emission of88.4 kg of CO2-e, meaning that the membrane contributes 3.23 ×10−3 kg CO2-e/m3 of water produced. Using these values, the calculatedtotal process contribution of the membrane modules is between 0.18and 0.07% for the lowest and highest process emission cases respective-ly. This contribution increases with decreasing membrane lifespan,but even with a 3 year replacement frequency, the contribution onlyreaches 0.45%. As a result of this comparison, which included the mostdetailed public LCA of membrane manufacturing to date, it is safe toassume that membrane manufacturing impacts are negligible whenconsidering overall SWRO process emissions. However, these numbersare more of an indication of the extreme energy requirements of theRO process, rather than the insignificance of membrane manufacturingimpacts.

4.4. Comparison of end-of-life scenarios

The primary goal of this study was to determine which end-of-lifeoptions for used ROmembranes originating at Australianmunicipal sea-water desalination plants, are the most environmentally favourable.Fig. 4 shows the impact of each disposal scenario for climate changeand fossil fuel deletion relative to membrane manufacturing. Absolutevalues and other impact categories can be found in Table S1 of thesupporting information.

The impact of landfill is relatively small when compared tomembranemanufacturing, which is expected, due to the inertmaterialsand short transportation distances. Even though the polymeric mem-brane components are mostly inert, there is still a degradation of 1–5%of the material during the 100-year-surveyable time period [63].While small, this effect and the transportation of the membranes fromthe plant to the landfill location, contribute to the CO2-e emissionsand resource use of landfill disposal.

The results show that the reuse scenarios are highly environmental-ly favourable across the studied impact categories. Direct RO reuse hasboth the greatest reduction in CO2-e emissions and fossil fuel depletionof all the scenarios, with conversion to UF scenario is only slightlybehind, due to the extra chemical treatment steps involved.

While the reuse scenarios gain the benefit from avoided productionof virgin membranes, the recycling scenario gains environmental creditfrom the offset of virgin plastic production. The results show that afterthe reuse scenarios, recycling has the greatest environmental benefit.The recycling of the PET permeate spacer and PP feed spacer generatesa CO2-e emissions saving of 0.93 and 1.25 kg CO2-e per kg recycled,respectively. This can be compared to the average benefits reported bythe Australian recycling sector, which are stated to generate a savingof 1.07 and 1.64 kg CO2-e per kg recycled for PET and PP respectively[53]. The recycling of ABS provided a considerably higher offset of2.5 kg CO2-e per kg due to the higher energy requirements for themanufacturing of virgin ABS [64]. Close agreementwith those previous-ly reported values adds to the validity of these comparisons and theviability of the recycling scenario as an alternative disposal option forend-of-life membranes.

The scenarios of incineration, syngas production and EAF are underthe category of energy recovery. While the incineration scenariogenerates significant electricity production,which offsets fossil resourceconsumption, the combustion and subsequent release of flue gas gener-ate considerable CO2-e emissions. The gasification process provides amodest environmental benefit across all impact categories, which isgained from electricity production through the combustion of thegenerated syngas. While the benefits are small when compared to the

-30

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0

5

10

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Landfill Incineration Gasification EAF Recycling Conversion to UF

Direct RO reuse

Rela

tive Im

pact (%

)

Climate change potential

Fossil fuel depletion

Fig. 4. Greenhouse gas emissions and resource depletion for the disposal of one RO membrane element. Results are displayed in terms of relative offset of membrane production.

51W. Lawler et al. / Desalination 357 (2015) 45–54

reuse and recycling scenarios, this model suggests that gasification isfavourable over incineration.

The third energy recovery scenario is the use of the membranematerial as polymeric carbon source in EAF for steelmaking. Unlike theincineration and gasification scenarios, this process does not gain itsbenefits from electricity generation, but rather from negating the useof metallurgical coke. This offset includes the required mining, process-ing and transportation of the coke to steel mill. While the EAF scenariodoes provide a positive emissions offset of 3.5 kgCO2-e, themain benefitcomes from the reduction in non-renewable resource use with an offsetof 6 kg oil-e.

When comparing the various scenarios, it is important to determineif the differences between them are significant, given the uncertaintiesin the model. The pairwise Monte Carlo method used in this study con-firmed statistically significant variations in CO2-e emissions between allend-of-life options, apart for the difference between gasification-EAFand gasification-recycling. In terms of fossil fuel consumption, resultsshow that only 5 out of the 21 comparisons are not significant. Thisincludes, incineration-EAF, incineration-recycling, EAF-recycling, EAF-UF conversion, and most notably UF conversion-direct reuse. Thesimilarity in the EAF pairs is attributed to theuncertainty in data relating

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Landfill Incineration Gasification

CO

2-e

emis

sion

s pe

r m

odul

e (k

g)

Transport

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Fig. 5. Contribution of transportation and process to the clim

to the extraction and processing of metallurgical coke, and the assump-tions regarding coke substitution rates. Regarding the reuse scenarios,the difference in CO2-e emissions is statistically significant; however,the difference of fossil fuel depletion falls just short of significance,due to the similarities in the scenarios.

Overall, all end-of-life options studied, apart from incineration, showa reduced environmental impact over landfill. The options of incinera-tion, gasification and EAF treatment, have limited large scale implemen-tation in Australia, making their adoption for end-of-life membraneschallenging. Additionally, depending on the condition of the mem-branes, the direct reuse option is the simplest programme to implementwith minimal processing, giving it additional advantages over otheroptions. The highly variable assumptions of membrane secondarylifetime and transportation distance, on which the reuse scenarios arebased, are explored in further details in the following sections.

4.5. Effect of transportation distance and reuse membrane lifespan onend-of-life scenario viability

Due to Australia's size and coastal population distribution, the vari-ous municipal seawater desalination plants are located towards the

EAF Recycling Conversion to UF

Direct reuse

ate change (CO2-e) emissions of the different scenarios.

52 W. Lawler et al. / Desalination 357 (2015) 45–54

coast and are a significant distance apart. For the end-of-life scenarioswhere the used membranes require substantial relocation, transporta-tion emissions have the potential to play a significant role in thescenario's environmental sustainability. Fig. 5 shows the contributionof each scenario's transportation and how it affects the benefits of theprocess, and also show the difference between the transportation sce-narios. The bars represent the results from the average transportationdistancewith the error bars representing the results from themaximumand minimum distances.

While the reuse methods have the highest environmental benefit,they also feature the most strenuous transportation scenarios. Usingthe average transportation distance of 2480 km, the reuse transportscenarios contribute 3.73 kg CO2-e to the atmosphere with between0.11 and 6.85 kg being emitted for the low and high cases respectively.Energy recovery through EAF has a similar transportation impact withan average of 2.65 kg CO2-e being emitted with a high and low of 6.11and 0.1 kg respectively. The scenarios only requiring local transporta-tion of 47 km, such as landfill, incineration, and gasification have alow impact of 0.232 kg CO2-e emitted, with the recycling scenariohaving a slightly higher emission of 0.42 kg CO2-e.

As the transportation distance required for the reuse scenarios ishighly variable, it is important to understand how this affects emissionsand to calculate the maximum distance that they can be transported,while the options is still environmentally favourable. Fig. 6 shows theeffect of increasing transportation distance on the CO2-e emissions asso-ciated with the relevant reuse scenarios, contrasted to landfill disposaland recycling. Additionally, as it has already been identified that thereuse lifespan of the membrane has a significant impact on reuse sus-tainability, a number of membrane lifespans have been included.

As expected, CO2-e emissions rise with increasing transportationdistance and decreasing membrane lifetime. The results show thatmembranes which have been converted to UF, and only last half ayear, produce higher emissions than landfill at all transportationdistances. If the converted membrane is reused for one year, it can betransported up to 1537 km before disposal in landfill is more environ-mentally sustainable. Similarly, a directly reused membrane lastingonly half a year will generate higher emissions than landfill iftransported more than 1173 km. It has been identified that 4550 km isthe maximum reasonable transport distance required for a membraneto be reused within Australia. Therefore, membranes directly reusedwhich last at least 11 months and UF converted membranes lasting atleast 1.4 years, will be more environmentally beneficial than landfill atall possible transportation distances. The greater emission offsets thatthe recycling scenario offers mean that substantially shorter distancesor longer lifespans are required to make reuse comparably morebeneficial.

65

70

75

80

85

90

95

100

0 1000 2000

kg C

O2-

e em

issi

ons

per

mod

ule

Reused membrane transporta

Fig. 6. Effect of transportation distance on the viability of reuse scenarios relative to m

Alternative transportation modes were also considered for themembrane reuse scenarios including domestic shipping and transporta-tion by rail. Overall, all three transportation methods have relativelysimilar impacts, with sea and rail being slightly favourable over road,while road is more practical in the case of used RO membranes (seesupporting information Fig. S1 for more details).

4.6. Effect of end-of-life scenarios on landfill loading

One of the primary goals of this study is to reduce the burden thatmembrane disposal has on landfill, and therefore it is important toconsider the waste streams of each scenario. To do this, and to avoidthe difficult and inherently subjective nature of estimating landuse [65], the total mass of the final waste to be disposed is used(shown in Fig. 7). This includes components that are not suitable forthe given scenario (e.g. the fibreglass case in EAF) and the residuefrom the processes themselves (e.g. slag from the gasification and incin-eration processes).

As expected, the landfill scenario involves the highest mass of mate-rial to be disposed of, with the entire 13.5 kg (dry mass) module goingto landfill. While the reuse scenarios do not directly require any massto be sent to landfill, the membranes still need to be disposed of afterthe second lifespan. Therefore, the mass is calculated from the avoidedmembrane disposal that comes from extending the membrane usefullifetime, and as a result, the reuse scenarios have the second highest im-pact on landfill. This is an interesting contrast to the LCA results whichdemonstrated that the reuse methods are heavily environmentallyfavourable and highlights one of themajor disadvantages of membranereuse.

The recycling scenario still requires the disposal of 8 kg ofmaterial as40% of themembranemodule is unsuitable for this application. Similar-ly, the contribution from the EAF process is mainly comprised of thedisposal of the fibreglass casing, which cannot go into the furnace. Thegasification scenario produces substantial residue due to the incompletecombustion taking place and the incineration process produces up to1 kg of slag requiring landfill. The majority of the waste from the gasifi-cation and incineration processes comprise of residual silica from thefibreglass casing.

While the reuse and thus lifecycle extension of the membraneprovides many environmental benefits, it does not reduce the amountof material requiring eventual disposal to the same extent as the otherscenarios. If the absolute priority is the aversion of waste from landfill,over all other impacts, then incineration is the most beneficial option.This is the main reason that incineration is commonly used whereland space is at a high premium, such as Singapore and Japan [39].

3000 4000

tion distance (km)

Landfill

Recycling

UF - 0.5 yr

UF - 1 yr

UF - 2 yr

RO - 0.5 yr

RO - 1 yr

RO - 2 yr

embrane reuse lifetime (RO: direct reuse, UF: membrane conversion then reuse).

0

2

4

6

8

10

12

14

16

Landfill Incineration Gasification EAF Recycling Direct reuse

Conversion to UF

Mas

s go

ing

to la

ndfil

l per

mod

ule

(kg)

Fig. 7.Mass of waste material requiring landfill disposal for each of end-of-life scenarios for one RO membrane.

53W. Lawler et al. / Desalination 357 (2015) 45–54

5. Conclusions

The results of this study show that direct reuse is the most environ-mentally favourable option for end-of-life membranes, and that landfillis the least favourable option. In terms of aversion ofwaste from landfill,incineration results in the least mass requiring disposal, while the reusescenarios feature the greatest impact. Although the most environmen-tally favourable option, due to its virgin membrane production offset,it is clearly highlighted that the reuse option does not target the actualdisposal of the membrane module, and is highly dependent of reuselifespan. The results also show that recycling and disposal in EAF areboth relatively favourable options, with EAF being particularly suitablefor the minimisation of waste volume.

While the study focuses on the Australian geographical setting, theprincipal findings can be easily applied to the international context. Inaddition to the relevance for RO reuse and recycling, this LCA study isa valid comparison of traditional disposal scenarios for all plastic solidwaste. Thus, it can be used in future studies and policy making ongeneral waste management decisions.

Overall, this study provides valuable insight into the end-of-life ROmembrane options that are currently being considered for furtherdevelopment. It shows the potential environmental benefits that couldbe realised through an organised reuse system and encourages thedevelopment of a membrane disassembly and component recyclingsystem for final disposal. This study will provide valuable informationfor membrane users in selecting end-of-life options, as it containedwell defined criteria for the environmental viability of each option.

Acknowledgements

The authors acknowledge the financial support of the NationalCentre of Excellence in Desalination Australia, which is funded by theAustralian Government through the National Urban Water and Desali-nation Plan. Collaborative partners from Monash University, SydneyWater, Water Corporation, Dow and the SkyJuice Foundation are alsogratefully acknowledged.

Appendix A. Supplementary data

Information on additional impact categories for end-of-life scenarioemissions, membrane element material compositions, descriptionof transportation scenarios, seawater desalination CO2-e emissions,impact of alternative transportation methods, and life cycle inventorydata, can be found in the supporting information. Supplementary dataassociated with this article can be found, in the online version, athttp://dx.doi.org/10.1016/j.desal.2014.10.013.

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