Environmental and economic evaluation of end-of-life reverse osmosis membranes recycling by means of chemical conversion

Accepted Manuscript Environmental and economic evaluation of end-of-life reverse osmosis membranes recycling by means of chemical conversion Eduardo Coutinho de Paula, Míriam Cristina Santos Amaral PII:

S0959-6526(18)31435-5

DOI:

10.1016/j.jclepro.2018.05.099

Reference:

JCLP 12956

To appear in:

Journal of Cleaner Production

Received Date: 13 December 2017 Revised Date:

5 May 2018

Accepted Date: 12 May 2018

Please cite this article as: Coutinho de Paula E, Santos Amaral MíCristina, Environmental and economic evaluation of end-of-life reverse osmosis membranes recycling by means of chemical conversion, Journal of Cleaner Production (2018), doi: 10.1016/j.jclepro.2018.05.099. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Environmental and economic evaluation of end-of-life reverse osmosis membranes recycling by means of chemical conversion

Eduardo Coutinho de Paula*, Míriam Cristina Santos Amaral

* Corresponding author:

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E-mail address: [email protected]

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Department of Sanitary and Environmental Engineering, Federal University of Minas Gerais, Av. Antônio Carlos, n° 6627, Pampulha, Belo Horizonte, Minas Gerais, Brazil.

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7,207 words Environmental and economic evaluation of end-of-life reverse osmosis membranes recycling by means of chemical conversion ABSTRACT

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The use of reverse osmosis (RO) membranes has been significantly increasing because RO technology is a great option for the production of clean water for both domestic and industrial purposes, among water stress conditions and scarce clean water resources. The main solid waste from RO plants is membrane elements, which are often disposed

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of in landfills, and the large amount of waste needs to be properly managed. The objective of this study was to evaluate the environmental and economic gains of

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implementing end-of-life RO membrane recycling. The method applied the Material Input per Service Unit (MIPS) eco-efficiency tool. The recycling technique was based on chemical oxidation of thin-film-composite (TFC) RO membranes and was applied by immersion in a commercial sodium hypochlorite (NaClO). The recycled membrane showed similar performance and characteristics to porous membranes. Based on current market costs, the replacement of a new ultrafiltration membrane spiral element (with an

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average lifespan of 5 years) by the recycled membrane (with an estimated lifespan of 2 years) for water treatment results in monetary savings of 98.9%. MIPS indicated that chemical conversion of one 8-inch spiral element of an end-of-life RO membrane with 13.5 kg results in 2,609.81 kg of materials not being polluted or withdrawn from the

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environment. The most important conclusion of this study is the possibility to have economic gains, associated with environmental benefits, arising from the use of

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recycled membranes.

Keywords: reverse osmosis, waste, membranes recycling, environmental gains, economic gains, sustainability.

1. Introduction

Reverse osmosis (RO) technology is playing a growing role in meeting water supply and water treatment needs worldwide, primarily due to its process maturity, reliability, simplicity, its current cost, the higher water recovery it allows for and its lower energy consumption when compared to other available desalination and demineralisation processes (IDA, 2014; Liyanaarachchi et al., 2014; Ismail et al., 2015; Shenvi et al.,

ACCEPTED MANUSCRIPT 2015). The extent to which the role of RO membrane will further expand depends in part on the cost-effectiveness of this technology and the available alternatives. Despite the major advancements in RO technology, the desalination industry is still facing significant practical issues and challenges regarding membrane sustainability. Increasing RO membrane application means also increasing potential adverse impacts.

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Energy footprints, salt-concentrate disposal options, other waste recycling, and environmental and health concerns are among the top concerns shaping the adoption of this technology (Liyanaarachchi et al., 2014; Rattanakul, 2012; Joo, Tansel, 2015; Shrivastava et al., 2015).

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At the same time, sustainable management has become a key topic in the sustainability literature and eco-efficiency has become a buzzword in the industry. Eco-efficiency aims at improving the environmental and economic efficiency of companies, attaining a

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higher value with fewer inputs, materials and energy, and more output with less waste. Thus, companies aim at implementing clean technologies within the industry itself or at other points in the supply chain and at reducing ecological impacts and resource intensity. This is achieved by practices such as using reverse logistics programs to reduce pollution through reuse and recycling and thus substituting new materials for

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recycled ones, producing significant energy savings and reducing pollution (Kong et al., 2012; Kurdve et al., 2015; Henriques and Catarino, 2015; ISO, 2011). Therefore, science and technology have an important role in addressing the pressing sustainability challenges by providing the appropriate solutions.

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The evaluation of the sustainability of industrial products should include criteria across the product life cycle: the sourcing and extraction of natural resources; material transportation to the manufacturing facility; manufacturing of the product from its raw

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material components; and use of the product and end-of-life management, including the disposal, reuse or recycling of the product at the end of its useful life. A technical standard to enhance sustainability provides a means to track incremental changes to the product’s sustainability profile and provides a framework to compare and assess the sustainable nature of different products performing similar functions, such as: product design, durability (long-term value), product manufacturing, corporate governance and innovation. In this context, Life Cycle Assessment (LCA) and other eco-efficiency tools have been used to provide better alternatives in terms of their environmental impacts. LCA is a systems-based method used to determine the adverse potential impacts to the

ACCEPTED MANUSCRIPT environment, associated with a product throughout its life cycle. The principles and stages of LCA are described in ISO 14040 (ISO, 2011). Conclusions from LCA studies can be applied to support decisions ranging from product design to public policy, and all relevant inputs (e.g. raw materials, energy) and outputs (e.g. emissions, waste) to the product system are evaluated to estimate impacts. The LCA method has been applied to

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the membrane industries (Zhou et al., 2011; Plappally and Lienhard, 2012; Lawler et al., 2015; Shahabi et al., 2015). However, the numerous categories of environmental impacts used in LCA focus mostly on output-based aspects, while the use of natural resources is not covered comprehensively (Wiesen et al., 2014; Gleiber et al., 2016).

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Additionally, results from this range of environmental categories are not easy to understand and to communicate, which is a key requirement for a comprehensive ecological indicator (Giljum et al., 2011 Gleiber et al., 2016).

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The fast-growing industrial implementation of membrane technology, the diffusefeasibility studies for membrane applications in prominent areas (such as energy recovery) and the use of membranes based on the incorporation of nanoparticles, carbon nanotubes or graphene in a large range of applications, indicate their promise as innovative desalination technologies, particularly for water treatment, due to the

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increasing water demand on a global scale (Buonomenna, 2013; Subramani and Jacangelo, 2015). Membrane technology has to face the need to evolve towards an even more productive process and to adhere to more stringent environmental regulations. The main solid waste from RO plants is membrane elements, which normally have a

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limited life cycle, of approximately 5 to 7 years (Ziolkowska, 2015), and are most often disposed of in landfills. According to Landaburu-Aguirre et al. (2016), more than 840,000 end-of-life RO membranes are discharged annually at worldwide (equivalent to

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>14,000 tonnes·year−1). The lack of economically and ecologically feasible waste management options is a challenge for the widespread implementation of RO technology sustainability. Recent research papers have underlined the importance of seeking a solution to this environmental impact, that is, the need to limit the direct discarding of these elements (Rattanakul, 2012; Lawler et al., 2015; Sahuquillo et al., 2015; Landaburu-Aguirre et al., 2016; Coutinho de Paula and Amaral, 2017). The technical evaluation of end-of-life RO membranes recycling has been reported in previous studies (Prince et al., 2011; Lawler et al., 2011; Lawler et al., 2012; Raval et al., 2012; Lawler et al., 2013; Ambrosi and Tessaro, 2013; Pontié, 2014, GarcíaPacheco et al., 2015; 2018; Coutinho de Paula et al., 2016; Coutinho de Paula et al.,

ACCEPTED MANUSCRIPT 2017a; Pontié et al., 2017). Although previous studies had made substantial contributions, there is a lack of understanding on how the studies can measure the environmental and economic gains of recycling. Thus, it is necessary to identify and better understand the contextual factors that influence the environmental and economic aspects regarding end-of-life RO membrane sustainability.

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Against this background, the main objective of this research was to evaluate the environmental benefits using the Material Input per Service Unit (MIPS) method. This concept was developed 20 years ago as a measure for the overall natural resource use of products and services. The MIPS approach is used for micro level application for

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assessing value chains, supporting business management, and operationalizing sustainability strategies (Liedtke et al., 2014). MIPS gives the amount of materials (including energy in terms of the material required) needed for a specific benefit in mass

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units (kg or tonne). This approach methodology is a practical, easy to handle and their simplicity could be interesting for quick assessments due to provide quantitatively captures pressures induced on the environment by a specific production-consumption system and can thus serve as a pressure or eco-efficiency indicator. By focussing on pressures (such as resource consumption, wastes, emissions) rather than impacts (such

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as acidification, global warming etc.), the MIPS methodology is geared towards measuring and improving the resource efficiency of products. Reducing resource use and emissions generated by a product effectively reduces the pressure a product exerts on the environment (Gleiber et al., 2016). Compared to specific environmental

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evaluations like LCA, MIPS has a lower level of detail and a quantitative evaluation of environmental pressure only, and is thus less labour-intensive (Saurat, Ritthoff, 2013). In addition, results of the MIPS approach are easy to understand by non-specialist

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audiences, which facilitates their communication and implementation within a company (Saurat, Ritthoff, 2013). The MIPS approach provides relevant knowledge on resource and energy input at the micro level for fact-based decision-making in science, policy, business, and consumption (Wiesen et al., 2014; Liedtke et al., 2014; Saurat, Ritthoff, 2013). This paper brings at least three key contributions to the literature regarding the recycling of RO membranes. First, the study adapts and applies the MIPS method to recycled membranes; second, an economic assessment of recycling end-of-life RO membranes is conducted; and finally, a comparison between the environmental and economic gains is presented and discussed.

ACCEPTED MANUSCRIPT 2. Materials and methods

2.1 Recycled membrane characteristics An end-of-life membrane that has been previously recycled is a thin film composite

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(TFC) RO membrane, with an aromatic polyamide (PA) active layer, a polysulfone (PSf) support layer and a polyester (PET) base. It is commonly used in desalination and demineralisation processes around the world. The recycling technique is simple, and it is based on oxidative treatment of a TFC RO membranes in order to remove its dense

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PA layer and expose the PSf support layer. This method is the most common for RO membranes recycling (Lawler et al., 2013; García-Pacheco et al., 2015; 2018; Coutinho de Paula et al., 2016; 2017a). The PA layer is oxidized and dissolved into the chemical

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solution applied. The experiments were performed with a bench scale unit, conducted in triplicates, and used commercial sodium hypochlorite (NaClO) 10-12%. The contact was by immersion for 2.7 hours (contact intensity ~300,000 ppm·h) at room temperature (25 °C). The both cleaning and recycling membrane procedures have been established and standardised during previous studies (Coutinho de Paula et al., 2017a). Membrane

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cleaning was performed at room temperature in two stages; stage 1 involved immersion with 0.1 wt.% NaOH and stage 2 immersion with 0.2 wt.% HCl for 15 hour each stage. The NaClO bath presented high physical and chemical stability (yellow color, typical odor, pH and effective free chlorine), and showed a capacity for reuse by successive

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treatments of 36 batches of membranes, with three membranes each (Coutinho de Paula et al., 2017a). The NaClO bath used a hermitic storage container and the addition of commercial NaClO was not necessary for three weeks. In order to treat the oxidizing

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waste (exhausted NaClO solutions), sodium thiosulfate (Na2S2O3) has been used successfully (Coutinho de Paula et al., 2017a). The performances of both end-of-life and recycled membranes were investigated by cross-flow water permeation measuring. The recycled membrane showed similar performance and characteristics to porous membranes (low pressure processes) that are used in microfiltration (MF) and ultrafiltration (UF) processes, with a permeability between 81 ± 17 and 117 ± 49 L·h-1·m-2·bar-1 (equivalent to 224·10-12 - 343·10-12 m3·s1

·m-2·Pa-1) according to Coutinho de Paula et al. (2017a). In addition, an alkaline

cleaning at room temperature (25 °C) proved efficient in recovering permeability during successive cycles of fouling and cleaning for 150 hours. The evaluation of the removal

ACCEPTED MANUSCRIPT efficiencies showed turbidity and color separation properties that give added value to the recycled membranes, as well as a total microbiological parameters removal. These results were discussed in detail by Coutinho de Paula et al. (2017a; 2017b; 2017c).

2.2 Environmental and economic evaluation

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In line with the objective of this paper, the present study was conducted in three stages: data collection, environmental evaluation and economic assessment. The 8-inch spiralelement RO membrane is very common in desalination plants around the world and it was considered as the unit basis. As a case in point, for a desalination plant producing

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410 million litres per day (equivalent to 410 · 106 L·daily-1), consisting of 60,000 8-inch RO elements, which are replaced every 7 years (or 15 % per year), a disposal and replacement of 9,000 elements per year takes place. Thus, the environmental and

life RO membranes elements.

2.2.1 Environmental evaluation

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economic evaluations were based on a case study that replaces annually 9,000 end-of-

In the first stage, data collection, the masses of resources were measured. The data

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sampling consisted of recording the mass of waste material and recycled material. Furthermore, the mass balance was developed, to calculate the mass of materials (kg) and quantify the total use of resources.

To estimate the environmental benefits, this study applied a material intensity analysis

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using the method developed at the Wuppertal Institute (Saurat and Ritthoff, 2013; Wuppertal Institute, 2014). The MIPS method allows for the assessment the environmental changes associated with the extraction of resources from their natural

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ecosystems. Thus, the second part of the study consisted of a material input assessment to evaluate the environmental impacts of the processes. The MIPS is calculated by considering the entire life cycle of a product and represents the total material input that individuals move or extract from nature for the production of goods and the delivery of services. Material inputs include four main categories: biotic raw materials, abiotic raw materials, water and air. Biotic raw materials include all agriculture and forestry products, along with the biomass that is eliminated but not used during product processing. The abiotic raw materials category contains all minerals and ores removed in mining operations, as well as any related earth movements. All fossil fuels are included in this category and are

ACCEPTED MANUSCRIPT measured in mass units. Humans also interfere with the flow of fresh water on the planet. Thus, the MIPS method considers all extracted or used freshwater flows, including the utilisation of ground and surface water, cooling water in industries, water for irrigation in farming and rivers diverted to other courses. Finally, all air that is chemically treated or transformed into another physical state is considered in the air

Ritthoff, 2013; Wuppertal Institute, 2014).

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category. This last category is strongly correlated with CO2 emissions (Saurat and For any given resource, the (Wuppertal Institute, 2014) has defined the quantity of mass in each category, also known as the mass intensity factor (MIF). As a result, the MIPS is

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calculated by multiplying the resource mass by its respective MIF per category, as per equation (1).

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MIPS = mass · MIFBiotic + mass · MIFAbiotic + mass · MIFWater + mass · MIFAir

(1)

Similar MIPS calculations has been already adopted by several authors and applied in several fields, especially to Cleaner Production Programmes (Oliveira Neto et al., 2016; Monaco and Di Matteo, 2011; Spinelli, et al., 2013), involving recycling (Oliveira Neto

Junior, 2016).

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et al., 2014a; 2015) and reverse logistics (Oliveira Neto et al., 2014b; Dias and Braga

2.2.2 Economic aspects

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In the third stage, the costs of both alternatives (new membranes and recycled membranes) were estimated. A costing of the RO membranes recycling technique was performed, including reagents, energy, treatment and disposal of effluents (depleted

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NaClO solutions). Subsequently, a comparison was made of the market costs of new membranes and recycled membranes. In addition, a preliminary study was conducted to estimate the capital and operational expenses (CapEx and OpEx) of the oxidative treatment system. The recycling system is very simple and it would require a feed pump that would pump the oxidizing agent to the pressure vessel, CIP (cleaning in place) tank with dosing units for chemicals (acid and alkaline cleaning products), measuring equipment (flow and pressure meters), and an effluent buffer tank to store the wastewater. Membrane replacement costs considered an average membrane lifespan of 5 years while the recycled membrane lifespan is estimated in 2 years (Lawler et al., 2015). The

ACCEPTED MANUSCRIPT membrane prices were provided by a large commercial membrane supplier. The oxidizing agent used was commercial NaClO (10-12%) and the cleaning agents used were NaOH solution at 0.1% w/w and HCl (37%) solution at 0.2% w/w, which has an approximate price of US$ 0.50/kg, US$ 3.00/kg and US$ 12.00/kg, respectively. The volume of NaClO and cleaning agents used were measured in order to recycling one

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spiral wound element. The electricity tariff was US$ 0.04/kW h. Personnel costs included one technician/operator and one assistant. Maintenance costs were estimated based on 5% per year from the initial investment cost.

Finally, environmental and economic benefits were compared, according to Oliveira

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Neto et al. (Oliveira Neto et al., 2014a; 2014b). The environmental gain index establishes for each unit of saved value that the economy of mass of environmental impact, while the economic gain index determines for each unit of saved value what the

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economy of certain amount of materials used.

2.3 Data collection

The environmental impacts of the recycling of end-of-life RO membranes were obtained utilising the MIF values per unit of resource used.

In order to evaluate the environmental gains, the 8-inch spiral-element RO membrane (1

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m long and 2.0·10-1 m in diameter, with a membrane area of 41 m2) was considered as the unit basis. The quantities (by mass) of polymeric materials and other materials that

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make up the membrane element are listed in Table 1.

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Table 1 – Composition of typical RO membrane elements Membrane element Composition component Feed spacer (9 %) PP (Polypropylene) Glues (7 %) PU (Epoxy resin or polyurethane) Membrane sheet (thin film Aromatic polyamide (0.2 µm) composite) (41 %) Microporous polysulfone (40 µm) Polyester support (120 µm) Outer casing (12 %) Fiberglass with polyester resin Permeate spacer (13 %) PET (Polyethylene terephthalate) Permeate tube end caps (17 %) ABS (Acrylonitrile butadiene styrene) Rubber o-rings (1 %) EPDM (Ethylene propylene diene) Total Adapted from Pontié (2014).

Mass (kg) 1.215 0.945 0.068 1.367 4.1 1.62 1.755 2.295 0.135 13.5

ACCEPTED MANUSCRIPT Table 2 presents the MIF values for abiotic, water and air category as provided by the Wuppertal Institute (2014).

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Table 2 – MIF values of polymeric wastes and other RO membrane element materials for abiotic, water and air categories MIF per category Abiotic Water Air Waste ABS (Acrylonitrile butadiene styrene) 3.97 206.89 3.75 Epoxy resin 13.73 289.88 5.50 Fiberglass (R-glass) 10.84 296.25 2.01 PA (Polyamide) 5.51 921.03 4.61 PET (Polyethylene terephthalate) 6.0 205.00 3.50 Polyester resin 4.32 166.96 2.43 PP (Polypropylene) 2.09 35.80 1.48 PU (Polyurethane) 7.52 532.39 3.42 SBR – rubber 5.70 146.00 1.65 Adapted from Wuppertal Institute (2014). Evidently, chemical cleaning agents and the NaClO used in the end-of-life RO membranes recycling present adverse environmental impacts. The manufacturing of NaOH and NaClO are energy intensive processes (Bindra et al., 2015), thus, Table 3 shows the list of MIF values, according to the Wuppertal Institute (2014), of other

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materials of interest in the present study.

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Table 3 –MIF values of chemical products used in membranes recycling for abiotic, water and air categories MIF per category Waste Abiotic Water Air Sodium hydroxide (NaOH) 2.76 90.31 106 Hydrochloric acid (37%) 3.03 40.66 0.38 Water 0.01 1.30 0 Chlorine (Cl2) 3.84 100.9 1.09 Sodium hypochlorite (NaClO) * 3.12 93.84 1.07 Sodium thiosulphate (Na2S2O3) ** 2.76 90.31 1.06 Adapted from the Wuppertal Institute (2014). * Factors obtained from the MIF values of the raw materials Cl2 and NaOH, rate 1:2. ** Assumed factors, similar to NaOH.

It is important to note that the material intensity studies developed by Saurat and Ritthoff (2013) and the Wuppertal Institute (2014) are based on the German energy mix, other European countries or world-average energy mixes. However, this does not

ACCEPTED MANUSCRIPT preclude the application of the methodological tool in other parts of the world, given that the quantitative values are very similar, according to the Institute. When the MIF values were established, the next step was to apply the selected ratios in equation (1) and calculate the environmental impact for each considered resource. The sum of each category results is the mass intensity per category (MIC). Afterwards, to

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evaluate the total intensity factor by each technology, the mass intensity total (MIT) was calculated, which is the sum of all categories. This quantification corresponds to the material that no longer impacts the categories due to the contribution of recycling. Finally, considering that the use of the recycled membrane in its new application

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corresponds to that of a porous membrane (low pressure), and assuming a similarity of composition between the RO membrane element and the UF spiral element, the present

3. Results and discussion 3.1 Environmental evaluation

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methodology adopted the RO element inventory as UF inventory.

In order to determine the mass inflow (recycled material per membrane element), the solid waste mass (kg) presented in Table 1 was multiplied by the corresponding

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dimensionless MIF (material intensity factor) value as indicated in Table 2. The MIPS are calculated by multiplying the resource mass by its respective MIF per category of natural resources (abiotic resources, water and air), as per equation (1). The results are

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presented in Table 4.

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Table 4 – Environmental gains obtained by the practice of RO membranes recycling, at a unit element base. Waste Recycled Material intensity per category Environmental (kg) gains per kind of material (kg) waste (kg) Abiotic Water Air ABS (Acrylonitrile 2.295 9.11 474.81 8.60 492.52 butadiene styrene) Epoxy resin 0.945 12.97 273.94 5.20 292.11 Fiberglass 1.62 17.56 479.92 3.26 500.74 PET 5.855 35.13 1200.28 20.49 1,255.90 Polysulfone 1.367 N.A.* N.A.* N.A.* PP (Polypropylene) 1.215 2.54 43.50 1.80 47.84 SBR (rubber) 0.135 0.77 19.71 0.22 20.70 Total 13.43 78.08 2,492.16 39.57 2,609.81 * Not available

ACCEPTED MANUSCRIPT Looking at Table 4, the values in the columns of abiotic materials indicate the masses that were avoided in the environment, while the values in the water and air categories indicate the amount of pollution reduced by the practice of recycling the membrane, on a unit element base. For example, by avoiding the direct discharge of 2.295 kg of ABS per membrane element and the IF of the abiotic being 3.97 (Table 2), it is estimated that

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9.11 kg of material stops polluting the environment. The Wuppertal Institute (2014) did not publish mass intensity factors for polysulfone, which is why it is not possible to accurately calculate the environmental gains resulting from the recycling of an end-of-life RO membrane element. However, this fact does not

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affect the estimation of the other environmental gains.

As shown in Table 4, for each recycled RO membrane element, it is possible to avoid the production of 78.08 kg of abiotic materials, the contamination of 2,492.16 kg of

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water and the contamination of 39.57 kg of air. When considering the sum of the categories, it is calculated that 2,609.81 kg of material is neither polluted nor withdrawn from the environment per recycled RO membrane element. It is very important to consider that the PA layer is removed from end-of-life RO membrane for oxidative solution, then it should be considered a wastewater.

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From bench experimental results, Coutinho de Paula et al. (2017a) have present the material consumption (kg) of cleaning and oxidative agents have used in the end-of-life RO membranes recycling process. Thus, in order to conduct the present environmental evaluation, the material consumption was calculated using the 8-inch spiral-element RO

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membrane. Table 5 summarises estimates of the adverse environmental impacts caused by the recycling of one end-of-life RO membrane element, as developed in the present

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study.

Table 5 – Adverse environmental impacts caused by the practice of RO membranes recycling, on a unit element base. Material intensity per Environmental Waste Material category (kg) impact per kind of consumption waste (kg) (kg) Abiotic Water Air Sodium hydroxide 0.033* 0.091 2.98 0.035 3.11 0.1 % (cleaning) Hydrochloric acid 0.066* 0.20 2.68 0.025 2.91 0.2 % (cleaning) Water 22.0* 0.22 28.6 0 28.82 Sodium 0.92 * 2.87 86.33 0.98 90.18 hypochlorite

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10-12 % (recycling) Sodium thiosulphate 0.31* 0.86 28.0 0.33 29.2 (neutralisation) PA (polyamide) 0.068 ** 0.37 62.63 0.31 63.31 Total 23.37 4.61 211.22 1.68 217.51 * Value calculated from Coutinho de Paula et al. (2017a). ** According Table 1 (Aromatic polyamide 0.2 µm) from Pontié (2014). According to Table 5, the total environmental impact caused by the chemical cleaning and oxidative treatment of one end-of-life RO membrane element was estimated at 217.51 kg, including the neutralisation of the oxidant effluent. The total mass of the dry RO element is 13.5 kg. Considering the case of study that replaces annually 9,000 end-

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of-life RO membranes modules, the annual production of membrane waste is 121,500 kg.

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The application of recycled membranes is not the same as the initial (RO modules), and the recycled membranes may be used in other application. Employing more sustainable alternatives than simply disposing RO membranes should benefit the desalination industry. It could be considered as a material that can enter a “market” among industries or users. Besides, possibly providing low-cost membranes for less stringent applications represents another benefit to the water and wastewater treatment industry in general.

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The recycled membranes can be used in inexpensive MF/UF membrane replacements in water treatment projects, in low cost RO pretreatment, wastewater treatment operations in the industry, or in decentralized systems water treatment in rural areas (Coutinho de

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Paula and Amaral, 2017; Lawler et al., 2013). In the context of the present study, recycled membranes are intended to be used as substitutes for porous (low-pressure) membranes and therefore, the environmental gains

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should be estimated for the avoided new UF/MF membrane elements. Commercial polymer membranes of UF spiral element, are predominantly fabricated with polyethersulfone (PES). The Wuppertal Institute (2014) did not publish mass intensity factors for PES. However, assuming a similarity of composition between the RO membrane element and the UF element, both 8-inches, with a fiberglass outer casing, the same environmental gain per unit can be assumed, that is, 2,609.81 kg, as indicated in Table 5. It is necessary to deduct the adverse impacts caused by the recycling process (chemical oxidation), 217.51 kg, determining the environmental gain to be 2,392.3 kg per membrane element. Under these conditions, in the case of a replacement of 9,000 new UF membrane elements by recycled membranes, the environmental gain is

ACCEPTED MANUSCRIPT estimated at 21,530,700 kg of material that is neither polluted nor withdrawn from the environment. At this point, the mass of ~13 kg of the UF spiral element, which is similar to the RO element, should be taken into account. In other words, at the end of the operating life of the recycled membrane, compared to the use of the UF membrane, a bulk equivalent

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material will be destined for landfill. However, it is necessary to consider that the average lifespan of the recycled membrane is less than the lifespan of a new UF membrane. A previous study (Lawler et al., 2015) reported that end-of-life RO membranes converted to UF membranes and applied for pre-treatment on RO systems

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had their life cycle extension estimated at 2 years, which should be followed by landfill disposal. Table 6 presents a comparison of the waste to be sent to landfill annually.

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Table 6 – Comparison of the total annual waste to be sent to landfill. Unit New UF membrane Recycled membrane Membrane mass kilograms per 13.0 13.5 element Average lifespan years 5a 2b Annual replacement % 20 50 Annual mass kg 2.6 6.75 destined for landfill Total for 9,000 kg 23,400 60,750 elements a According to manufacturer information for use in the pre-treatment of RO systems or for the treatment of surface water for drinking and human-supply purposes. b According to the previous estimate (Lawler at al., 2015). Therefore, of the differences in total waste in the scenario of 9,000 recycled membrane

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modules (with a lifespan of 2 years) used to replace new UF membranes, a total increment material of 37,350 kg (159.6 %) is estimated. Although there is an increase of 37,350 kg· year-1 of landfill waste (due to the use of recycled membranes in the place of new UF membranes), it is important to consider that the mass of 121,500 kg of end-oflife RO membrane (equivalent to 9,000 elements of 13.5 kg each) was not sent to landfill due to the recycling, which results in a reduction of 84,150 kg. The results of this study showed the viability and applicability of the Wuppertal Institute (Saurat and Ritthoff, 2013; Wuppertal Institute, 2014) method to evaluate the environmental gains of end-of-life RO membrane recycling.

ACCEPTED MANUSCRIPT 3.2 Economic assessment Table 7 shows the quantities and the market prices of the supplies used during the chemical cleaning and the oxidative treatment of the discarded RO membrane, including the neutralisation of the oxidant effluent for the 8-inch spiral element RO membrane

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base (1 m long and 2.0·10-1 m in diameter, with membrane area of 41 m2).

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Table 7 – Quantities and prices of the supplies used to recycle the OI membrane, unit element base. Inputs Quantity (kg) Price Amount (US$/kg) (US$) a Sodium hydroxide (0.1%) 0.033 * 3.00 0.099 a Hydrochloric acid 37% (0.2%) 0.066 * 12.00 0.79 Water 22.0 * 0.00067 b 0.015 Sodium hypochlorite 10-12% 0.92 * 0.50 a 0.46 Sodium thiosulphate 0.31 * 2.03 a 0.63 Total 1.99 * Value calculated from Coutinho de Paula et al. (2017a). a From (ICIS, 2017). b From (ARSAE-MG, 2017). For the unit cost of $1.99 (US) for the recycling of a membrane element, which corresponds to US$ 0.15/kg, the cost of energy was not taken into account since the

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recycling process only involves immersion. But on a large scale a pump should be used to fill the elements with the cleaning solution and then for washing, the expended energy unitarily can be considered. Expenses regarding personal were considered, since

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in the case of a plant in operation, personal expenses are accounted for within the operating and maintenance expenses, and there are additional costs from membranes

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recycling. The resulting CapEex and OpEX of the recycling system is shown in Table 8.

Table 8 - Overview of the investment and operational costs for recycling method

CapEx

Description

Value (US$)

Feed pump Pressure vessel CIP tank with dosing units Flow and pressure meters Effluent buffer tank

500 1,400 300

Value (US$/Kg) -

200 150 2,550 -

0.153 0.147*

Total CapEx Capital cost amortization Water and chemicals

ACCEPTED MANUSCRIPT OpEx

Energy Labor Maintenance

Total OpEx * According to Table 7 ** Based on electric cost of 0.04 US/kWh

-

0.008** 0.228 0.028 0.564

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From Table 8, the total CapEx of the recycling system is estimated in US$ 2,550 and this value can be considered negligible in view of the adopting membrane recycling advantages. The estimate total OpEx is 0.56 US$ per kg of recycled material according to the experimental results of water, chemical and energy consumption. Considering

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that the spiral element is 13.5 kg, the total OpEx value corresponds to US$7.61 for one recycled module. Finally, assuming transportation costs at a 12 % of the price, each recycled membrane element costs $8.53 (US).

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The average unit market price for a new 8-inch spiral element polymeric membrane UF (1 m long and 2.0·10-1 m diameter with a membrane area of 39 m2) with a molecular weight cut-off (MWCO) of 10, 50 or 100 kDa, intended for pre-treatment applications in RO systems and surface-water treatment for potable use, is $980 (US) (equivalent to $25.13·m-2), according to the manufacturer (January 2017 database). These prices do

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not include taxes because of the different taxation practices in each country. From the estimated cost of $8.53 (US) to recycle each RO membrane element, the cost of $971.53 (US) per UF membrane element replaced by a recycled membrane (99.1 %) can be avoided. This estimated value does not account the economy with the non-destination

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for landfill.

It is important to consider that the lifespan of a new UF membrane and recycled

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membrane is 5 and 2 years respectively. A comparison of the initial investment and replacement costs for the membranes is shown in Table 9.

Table 9 – Comparison of initial investments, operational parameters and replacement costs. Unit New UF membrane Recycled membrane Membrane cost US$ per unit 980.00 8.53 a Average lifespan Years 5 2b Annual replacement % 20 50 Cost of annual US$ 196.00 4.24 replacement Total US$ 1,176.00 12.77 a According to manufacturer information for use in the pre-treatment of RO systems or for the treatment of surface water for drinking and human-supply purposes.

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According to the previous estimative (Lawler et al., 2015).

According to Table 9, the use of recycled membranes with an estimated lifespan of 2 years (Lawler et al., 2015), as a substitution for new UF membranes, results in a monetary savings of $1,163.23 (98.9%). As a study case, for a disposal and replacement of 9,000 elements per year takes place, annual savings of $10,469,070 (US) can be

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obtained. As expected, the costs of the management and transport of the recycled membranes as a waste at the end of the operation period in their new application will be postponed to the same period as the recycled membrane lifespan.

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3.3 Comparing the environmental gains with economic gains

Based on the presented results, it is possible to affirm that the recycling of RO

environmental and economic gains.

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membranes by the method proposed in the present study can be justified in terms of

To compare the environmental and economic gains, it is possible to determine the environmental gain index (EGI) by means of the ratio between the total material intensity (TMI) and the economic gain (EcG), while the economic gain index (EcGI) is determined by means of the ratio between the total saved material (TSM) and the EcG

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(Oliveira Neto et al., 2014a; 2014b). Table 10 shows the calculated gain indices for the scenario of 9,000 UF membrane elements replaced by recycled membranes for one year.

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Table 10 - Materials saved and gain indices (GI) for the recycling of 9,000 annual elements. Materials saved/gain indices Unit Value Economic gain (EcG) US$ 10,469,070 Total saved material (TSM) kg· year-1 84,150 -1 Total material intensity (TMI) kg· year 21,530,700 EcGI = TSM/EcG kg·US$-1 0.0080 -1 EGI = TMI/EcG kg·US$ 2.06

Table 10 shows that the monetary benefits of recycled membranes use are $10,469,070. In parallel, 84,150 kg· year-1 of materials were saved, equivalent to a total material intensity of 21,530,700 kg· year-1, when considering all categories. The FGI indicates that each dollar saved corresponds to a reduction of 0.0080 kg of material. From the point of view of a global scale, the EGI indicates that each dollar saved provides a

ACCEPTED MANUSCRIPT reduction of 2.06 kg of material that is neither modified nor withdrawn from the environment. Therefore, the environmental gains were higher than the economic gains. The practice of eco-efficiency is therefore a strategy able to generate environmental and economic gains. It allows for the reduction of costs with the use of recycled raw materials, the reduction of adverse environmental impacts, the reduction of waste and

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energy and water use, as well as for increased pollution control, in particular by reducing the disposal of materials in landfills and thus promoting sustainability.

In addition, by using recycled membranes, which are inexpensive, it is possible to obtain a cost reduction of the treated water. The costs of water treated by membrane

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separation processes depend on the installation and the operating costs of the water production system. In operational terms, electricity, membrane replacement, chemical cleaning of membranes, disposal of cleaning effluents, maintenance of the system and

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personal expenses are all part of the total costs. Evidently, the quality of the feed water and the capacity for treated water also influence the operational costs. In this broad context, the replacement of membranes would be less costly due to the sale of the recycled membrane for other purposes. The present study considered the recycled membrane application for water pre-treatment in RO plants, as presented in sections 3.1

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and 3.2.

There is very little investigation regarding environmental and economic impact of endof-life RO membrane recycling process. Lawler et al. (2015) looked at the environmental impact of a number of proposed end-of-life disposal options for RO

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membranes within the context of the Australian desalination industry, as follows: landfill, incineration, gasification, electric arc furnace, direct reuse, recycling, and oxidative treatment. According to these authors, the direct reuse scenarios are highly

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environmentally favourable across the studied impact categories, namely: climate change, fossil depletion, ozone depletion, ecotoxicity, human toxicity, freshwater eutrophication, marine eutrophication, and terrestrial acidification. RO reuse has both the greatest reduction in CO2-e emissions and fossil fuel depletion of all the scenarios, with oxidative treatment scenario is only slightly behind, due to the extra chemical treatment steps involved. While the reuse scenarios gain the benefit from avoided production of virgin membranes, the recycling scenario gains environmental credit from the offset of virgin plastic production. The LCA results from Lawler et al. (2015) showed that after the direct reuse scenarios, recycling has the greatest environmental benefit. For the end-of-life scenarios where the

ACCEPTED MANUSCRIPT used membranes require substantial relocation, transportation emissions have the potential to play a significant role in the scenario's environmental sustainability. Therefore, membranes directly reused which last at least 11 months and membranes converted by oxidative treatment lasting at least 1.4 years, will be more environmentally beneficial than landfill at all possible transportation distances (Lawler et al., 2015). The

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greater emission offsets that the recycling scenario offer mean that substantially shorter distances or longer lifespans are required to make reuse comparably more beneficial.

Some studies have shown that the exclusion of a detailed transportation model in an LCA study can result in a severe underestimation of the environmental impacts of waste

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disposal scenarios (Brambilla et al., 2009; Merrild et al., 2012). Compared to LCA, results of the MIPS approach, such as used in the present study of recycling RO membranes by means oxidative treatment, are easy to understand and to communicate,

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which facilitates their implementation within a water treatment plant (Wiesen et al., 2014; Gleiber et al., 2016; Giljum et al., 2011; Coutinho de Paula et al., 2017c). Finally, it should be noted that the spiral UF polymer membrane, according to the parameters reported by the manufacturer, has an average operational flow of 27 L·h-1·m2

(75·10-7 m3·s-1·m-2) in the typical pressure range of 5.55 to 9.31 bar (5.55·105 to

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9.31·105 Pa). At the same time, according to Coutinho de Paula et al. (2017a; 2017b; 2017c), the experimental results had indicated that the recycled membrane, when applied to the treatment of organic effluent, operating at 0.5 bar (0.5·105 Pa) at 25 °C, had a good fouling resistance, and a steady-state permeate flux of ~33 L·h-1·m-2 (91·10-7

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m3·s-1·m-2). In the same operation conditions, when applied in river-water treatment the permeate flux was ~60 L·h-1·m-2 (166·10-7 m3·s-1·m-2). Thus, there was a favourable evaluation for the viability of the recycled membrane module, not only in terms of water

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permeability, but in terms of separation capability. There is undoubtedly an environmental gain, however recycled membranes need to reach standards of operation and integrity that can reduce the environmental gain, because the uncertainty is not included, regarding a possible variability of permeate flow production, that is an opposed to the certainty of the manufacturer specifications of the RO products. Therefore, a new market can be found for the recycled elements. This study shows economic and environmental gains, and although there is some uncertainty with regard to amount of material saved and the prices of some materials, considerable efforts were made to reach the procedures for selecting variables and their respective characteristics. These were carefully selected to replicate the true method of

ACCEPTED MANUSCRIPT membrane recycling. A limitation of this research is that the chemicals, water and energy prices may vary depending on the time of the year and the place where it is to be used. The amount of chemicals depends on the type of foulant and the fouling severity of discarded membrane. If it is necessary to use twice the amount of chemicals estimated in Table 5, the estimate total OpEx of 0.56 US$ per kg (Table 8) increases to

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0.71 US$ per kg of recycled material, and the price of each recycled membrane increases from 8.53 $ to 10.75 $ (US). As a study case, for a disposal and replacement of 9,000 elements per year takes place, annual savings of $10,438,830.00 (US) can be obtained, or in other words, there is a reduction of only 0.29% in the EcG value (Table 10). Finally, the value of TMI (Table 10) decreases from 21,530,700 kg· year-1 to

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20,142,900 kg· year-1 (equivalent to a reduction of 6.45%), which corresponds to the EGI decrease from 2.06 kg·US$-1 to 1.93 kg·US$-1. At the same time, the TSM and

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EcGI values do not change (Table 10).

Therefore, the impact of chemical quantity uncertainty is small on the results and conclusions of this study. To the best of our knowledge, this is the first paper that report detailed methods to provide a tool to better understand and estimate environmental and economic benefits from membranes recycling, pointing to a circular economy on RO

4. Conclusions

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processes.

It is very important to take into account that the evaluation and selection of reuse or

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recycling alternatives should follow guidelines, not only regarding technical efficiency, but also regarding the associated environmental impacts. Several researchers have been developing technical studies on TFC membranes recycling, but the main gap observed

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in the literature relates to the lack of studies to assessing the environmental and economic aspects of implementing recycling techniques. The results obtained indicated that the recycling of RO membranes by means of chemical conversion brings about environmental benefits and monetary gains, due to the reduction of membrane replacement costs and the reduction of waste sent to landfills. In addition, this study presents some contributions to both membrane recycling theory and practice. Thus, this paper suggests a good approach to measuring the environmental impact reduction resulting from implementing membranes recycling. The main results and conclusions of this study are:

ACCEPTED MANUSCRIPT •

Based on current market costs, the replacement of a new UF membrane spiral element (with an average lifespan of 5 years) by the recycled membrane (with an estimated lifespan of 2 years) for water treatment results in monetary savings of 98.9%.

•

Based on the MIPS eco-efficiency tool, it was estimated that recycling by means

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chemical conversion of one 8-inch spiral element of an end-of-life RO membrane with 13.5 kg results in 2,609.81 kg of materials not being polluted or withdrawn from the environment. •

Considering a possible scenario of replacing 9,000 UF membranes per year with

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recycled membranes, a reduction of 84,150 kg of waste that would be destined to landfill can be obtained. Using the Wuppertal method, 84,150 kg of waste is equivalent to a total material intensity of 21,530,700 kg· year-1.

Another important result from this scenario indicated an annual monetary benefit of $10,469,070.

•

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•

In this case, each dollar saved corresponds to the reduction of 0.0080 kg of material. From the point of view of a global scale, each dollar saved provides a reduction of 2.06 kg of material that is neither modified nor removed from the

gains. •

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environment. Thus, the environmental gains were higher that the economic

Finally, according to the assessment of technical feasibility, with regards to the environmental and economic benefits, when implementing RO membrane

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recycling by means of chemical conversion, the RO technology could become

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more sustainable.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial or not-for-profit sectors.

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ACCEPTED MANUSCRIPT HIGHLIGHTS

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Environmental issues regarding end-of-life RO membranes disposal are presented. End-of-life RO membrane management in the near future may include recycling.

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Quantitative information regarding end-of-life RO membranes recycling by means of chemical conversion is provided.



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The possibility for environmental and economic benefits from implementing

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end-of-life RO membrane recycling is discussed.