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Journal of Cleaner Production, https://doi.org/10.1016/j.jclepro.2018.12.261

Environmental assessment of sustainable energy options for multi-effect distillation of brackish water in isolated communities

Raphael Ricardo Zepon Tarpania, Sara Miralles-Cuevasb,c**, Alejandro Gallego-Schmida,d*, Alejandro Cabrera-Reinab,c, Lorena Cornejo-Ponceb,c

a Sustainable Industrial Systems, School of Chemical Engineering and Analytical Science, The University of Manchester, The Mill, Sackville Street, Manchester M13 9PL, UK.

b Escuela Universitaria de Ingeniería Mecánica (EUDIM), Universidad de Tarapacá. Av. General Velásquez 1775, Arica, Chile.

c Laboratorio de Investigaciones Medioambientales de Zonas Áridas (LIMZA), Universidad de Tarapacá. Av. General Velásquez 1775, Arica, Chile.

d Tyndall Centre for Climate Change Research, School of Mechanical, Aerospace and Civil Engineering, The University of Manchester, Pariser Building, Sackville Street, Manchester M13 9PL, UK.

(*) Corresponding author 1: [email protected] ; [email protected]

(**) Corresponding author 2: [email protected]

AbstractAccess to sufficient quantities of fresh water is becoming increasingly difficult, especially in dry regions. Moreover, high levels of salinity, arsenic and boron are further limiting the access to quality fresh water in many isolated communities worldwide. This paper evaluates the life cycle environmental impacts of a small multi-effect distillation (MED) plant, treating brackish water with high levels of these metalloids in an isolated location in Northern Chile. The facility currently operates solely with electricity from a diesel generator and heat from a biomass boiler. In order to evaluate the environmental impacts of more sustainable energy options, the implications of the use of solar fields and grid electricity as potential alternatives have been analysed. The results demonstrate that coupling solar fields and grid electricity is the best option, sharply decreasing impact in most categories in comparison to the current operating mode of the plant. This was attributed to the impact savings from reducing/eliminating onsite diesel and biomass combustion, and their associated transportation to the plant. For MED desalination in off-the-grid areas, the use of solar energy is highly recommended as an alternative to complement the use of diesel and biomass, especially if the latter is not nearby the unit. The concentration of arsenic and boron was reduced to below the required standards for irrigation and livestock consumption. The article concludes that the use of solar energy and grid electricity are environmentally beneficial for the production of quality fresh water from brackish water using MED at isolated communities.

Keywords: life cycle assessment (LCA); desalination; arsenic; boron; solar and biomass energy; water treatment.

NomenclatureMED Multi-effect distillationRO Reverse osmosisRES Renewable energy sourcesLCA Life cycle assessmentFU Functional unitCOS Current operating strategy

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As ArsenicB BoronCCP Climate change potential (kg CO2-eq.)FDP Fossil fuels depletion (kg oil-eq.)MDP Metals depletion potential (kg Fe-eq.)ODP Ozone depletion potential (mg CFC-11-eq.)POFP Photochemical oxidant formation (kg NMVOC)PMFP Particular matter formation potential (kg PM10-eq.)FEP Freshwater eutrophication potential (g P-eq.)MEP Marine eutrophication potential (g N-eq.)FETP Freshwater ecotoxicity potential (kg 1,4-DB-eq.)METP Marine ecotoxicity potential (kg 1,4-DB-eq.)TETP Terrestrial ecotoxicity potential (g 1,4-DB-eq.)HTP Human toxicity potential (kg 1,4-DB-eq.)TAP Terrestrial acidification potential (kg SO2-eq.)

1. Introduction

Water is essential to sustain ecosystems and human activities. However, its availability has reached critical levels in many regions worldwide (Vörösmarty et al., 2010). This occurs due to excess water pollution, aquifer depletion and lack of novel water sources necessary for an increasing human population and economic growth (Bogardi et al., 2012; Wichelns, 2017). This situation is further aggravated in the context of climate change since it may add uncertainty to the dynamic of global water cycles (Rodell et al., 2018; Schewe et al., 2014). The current scenario requires better planning and novel strategies for a more rational use and exploitation of natural resources (Beck and Villarroel Walker, 2013; Giwa and Dindi, 2017), with an aim of reducing the number of people currently suffering with lack of freshwater (WHO and UNICEF, 2017).

Human health concerns arose in Latin American regions known for their high concentrations of arsenic (As) in the environment (Bundschuh et al., 2012). Similarly, but less intensely, concerns exist regarding the safe human exposure to boron (B) through the food chain (Meacham et al., 2010; Tagliabue et al., 2014). Long-term exposure to inorganic As, mainly through drinking-water and food, can lead to chronic poisoning and increasing skin cancer risks. Other adverse health effects that may be associated to its long-term ingestion include diabetes, pulmonary and cardiovascular diseases (WHO, 2011). Excess B is not common in the environment, but its surplus in humans has been linked to skin rashes, nausea, headaches, low blood pressure and metabolic changes. Studies on animal toxicity show that excess B may cause fertility issues and in crops may cause necrotic border in leaves (WHO, 2003).

Presently, many communities in Northern Chile lack access to freshwater in sufficient quantity and quality, especially the those located in the Atacama Desert, one of the world’s most arid regions (Cornejo et al., 2017). One example is the Taltape community in the Camarones Valley (a region of Arica & Parinacota), where nearly 30 people base their livelihood on agriculture and livestock. The drinking water for the population is supplied by a tank truck, while water for irrigation and cattle comes from the Camarones River, which presents high natural salinity, and As and B content. These metalloids are consequently transferred to farming products and, therefore, their broad distribution remains a source of concern due to their potential negative effects on human health (Albornoz and

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Cartes, 2009; Cornejo-Ponce, 2012). To increase access to quality water in isolated and dry regions, the desalination of seawater and brackish water has been increasingly suggested as a viable alternative, and has already been deployed in the region to increase its economic output (Cornejo-Ponce, 2016; Ghaffour et al., 2013).

The desalination of seawater and brackish water is nowadays a feasible source of fresh water. This process has become increasingly attractive economically due to technical developments experienced in the last decades. However, these techniques are not exempt of environmental and social problems (Gude, 2016). Desalination technologies through reverse osmosis (RO) has been the predominant worldwide (Ghaffour et al., 2013; Mezher et al., 2011). However, several obstacles such as specialized maintenance and high costs often impair its use in economically deprived regions (Burn et al., 2015; Schäfer et al., 2014). Technological and operational developments in thermal desalination, such as multi-effect distillation (MED), have made this technology increasingly attractive (Datsgerdi and Chua, 2018; Saldivia et al., 2019; Sharan et al., 2018). This is mainly due to its lower maintenance requirements, compactness and a high-quality product. Some of its disadvantages, such as high heat requirements, are being overcome with the use of renewable energy sources (RES), particularly solar-based alternatives (Abdelkareem et al., 2018; Chafidz et al., 2016; El-Sebaii and El-Bialy, 2015). Due to promising results, and the fact that this source of energy is frequently available in isolated and dry regions around the world, research on solar energy for desalination is plentiful (Chandrashekara and Yadav, 2017; Santosh et al., 2018; Shatat et al., 2013). In cases where solar energy show difficulties for harnessing and grid electricity is out of reach, the use of biomass can be a potential alternative to power MED systems in isolated communities. Nevertheless, the simultaneous use of different energy sources for MED is less explored (Ghaffour et al., 2015).

The environmental life cycle assessment (LCA) of desalination technologies such as MED, multi-stage flash and RO with the use of RES for seawater desalination have already been discussed in literature, evaluating large facilities in the European context (Raluy et al., 2006, 2005). More recently, LCAs have focused on RO technologies (Zhou et al., 2014). The present study goes beyond these scopes by providing the first detailed assessment of the impacts of a small-scale MED plant for brackish water desalination, suitable for isolated communities. For this purpose, the case of the Taltape MED plant is evaluated. The system is currently operated with electricity provided by a diesel generator and heat from a biomass boiler. The impacts of this mode of operation were calculated and compared to alternative scenarios, which includes solar fields (for electricity and heat generation) and the Chilean grid electricity. The concentration of As and B in the final distillate is discussed to evaluate the suitability of MED to increase the economic output of the Arica & Parinacota region. Therefore, this paper aims to evaluate the environmental impacts of energy options for MED treatments in Northern Chile, and also to discuss the implications for a more sustainable and cleaner production of quality fresh water from saline water in isolated communities worldwide.

2. Materials and methods

The LCA was carried out according to the ISO 14040/44 guidelines (ISO, 2006), following the attributional approach. The current operation of the Taltape MED plant and the assessed operating strategies for its energy provision are described below.

2.1. Goal and scope definition

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The goal of this LCA was to evaluate the life cycle environmental performance of a small multi-effect distillation (MED) plant with a production capacity of approximately 10 m3/day (or 3,680 m3/year) of distillate water in the Taltape community (Northern Chile). The influent is brackish water from the Camarones River. Presently, the current operation strategy (COS) of the MED unit uses electricity from a diesel generator and heat from a boiler fed with biomass pellets. To assess the changes in environmental impacts from using solar energy and grid electricity to assist the unit operation, the following alternative strategies for thermal and electric energy provision were studied:

Option A: diesel generator + biomass boiler + solar photovoltaic and thermal fields; Option B: grid electricity + biomass boiler; and Option C: grid electricity + biomass boiler + solar photovoltaic and thermal fields.

The functional unit (FU) of the study is “production of 1 m3 of distillate for agricultural purposes using the brackish water from the Camarones River”. The measured average total dissolved solids content of the Camarones River is 1,900 mg/L and it is decreased to less than 20 mg/L in the final distillate. The system boundaries were studied in a “cradle-to-grave” approach. The studied sub-systems are shown in Figure 1, and are commented below.

2.1.1. Taltape MED unitThe MED of brackish water comprises of a simultaneous set of evaporation processes and

subsequent condensation of vapours at decreasing temperatures corresponding to their saturation pressures. The Taltape MED plant has a total of eight effects with submerged tube heat exchangers provided by Aurum Processes Company S.L. (Murcia, Spain), through which steam flows as a source of thermal energy. The plant was manufactured and delivered by Inerco Tratamiento de Aguas S.L. (Madrid, Spain) in 2016. The MED plant is assumed to operate 24 h/day, producing 0.42 m3/h of distilled water from the catching of 24.3 m3/h of brackish water of the Camarones River.

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System boundaries Subsystems

Influent(Camarones river)

Return water(Camarones river)

Multi effect distillation unit

Multi-effect distillation

Refrigeration water

Sandfilter

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Distilled water(Taltape community)

Final condenser

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Figure 1 – Scheme of the multi-effect distillation (MED) plant flows in Taltape and the assessed options for energy supply.

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2.1.2. MED energy supply strategiesThe energy used in the MED unit is provided in two forms: electrical and thermal. The former

is used for the functioning of the pumps, boiler and facility instrumentation; the latter provides the energy needed to heat the brackish water.

2.1.2.1. Current operating strategy (COS)The COS and the Taltape MED were established by the Regional Government of Arica and

Parinacota (Cornejo-Ponce, 2016). The total electrical energy of the desalination system (12 kW) is divided as follows: 5 kW for the MED process, 6.5 kW for pumping and 0.5 kW for the biomass boiler. The total electricity consumption is 28.57 kWh/m3. Electricity is obtained by a diesel generator provided by Vielco (model KDE28S3 - energy output 17 kW) consuming 3.68 L/h of diesel. The boiler is provided by the company Nueva Energia (Metropolitan Region, Chile) and has a rated thermal energy output of 50 kW. It consumes biomass pellets provided by Proenergy S.L made of a mix of natural pine and eucalyptus with no additives, 5.9% moisture and 1.02% ash contents in weight basis, with a calorific value of 19.7 MJ/kg, originated from the Bio Bio region in the South of Chile. This equipment has an efficiency of around 90% when operating at 2 bar and 90°C.

2.1.2.2. Option A: energy provided by diesel generator + biomass boiler + solar fieldsIn this alternative, the energy sources used in the COS are complemented with solar energy,

reflecting its use in off-the-grid and isolated areas. During daytime (12 h/day) electricity is provided by solar photovoltaic panels (PVs) and heat by evacuated solar tube collectors (ETCs). The former consists of 10 panels (polycrystalline silicon, 60 cells per panel) with a total surface area of 15.8 m2. Four stationary lithium batteries (50 kg each) assist the electricity requirements of the system during cloudy weather. The latter comprises of seven modules with each containing 30 tubes. Each of the 30 tubular components is formed by two concentric glass tubes (internal diameters of 35 mm and 45 mm, 1.6 mm-thick) with a length of 150 cm, which contain inner copper-made tubes and assembling aluminium pieces. The solar fields equipment considered as a reference has been obtained from the company Solutechno Ltda (Lima, Peru).

2.1.2.3. Option B: grid electricity + biomass boilerIn this option, the thermal energy is provided only by biomass pellets, as in the COS. The

electricity from the diesel generator is substituted entirely by the Chilean grid, using a distribution network infrastructure expected to be implemented by the end of 2018 in the whole Camarones Valley.

2.1.2.4. Option C: grid electricity + biomass boiler + solar fieldsThis alternative considers 50% of the electricity requirements from the Chilean grid and 50%

from PVs. ETCs and biomass pellets provide the energy necessary for brackish water heating, also at equal shares.

2.2. Inventory analysis

Primary data of the life cycle inventory is based, unless otherwise stated, on information provided by equipment manuals, consumables suppliers and measurements carried out onsite. Background data have been sourced from the from Ecoinvent v3.3. database (Weidema et al., 2013)

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and the most up-to-date electricity mix of Chile has been considered (Gaete-Morales et al., 2018) (Table S1 in supporting information). A detailed and comprehensive description of the infrastructure of the MED unit can be found in the supporting information (Table S2). The infrastructure, consumables and energy use for the COS and the three herein proposed energy supplies can be found in Table 1.

The following assumptions have been made to fill data gaps and adapt some datasets: The biomass boiler used in Taltape was substituted by a furnace with the same heat output from

the Ecoinvent database. Due to the lack of background data, the cleaning agent of the MED unit, sulfamic acid, was

substituted by sulfuric acid. ETCs were assumed being made of glass, copper and heat transfer media. Other materials have

been excluded due to the lack of reliable data. The amount of distilled water for cleaning the unit (~2 m3/year) was excluded from the

assessment, insofar as this amount is less than 0.1 % of the functional unit volume. The MED subsystem (see Figure 1) materials were assumed to have a lifespan of 20 years. This

is a reasonable lifespan based on evaluations of seawater multi-stage flash desalination plants, which last up to 14 years without serious corrosion issues (Malik et al., 2015; Ravindran, 2012). The diesel generator set, biomass boiler and solar fields were also assumed to last 20 years.

At the end of their lifetime, the MED subsystem and ETCs materials are predicted to be decommissioned and landfilled. The isolated location of the plant and wear of materials would result in low environmental benefits from the recycling process.The anti-crusting and cleaning agents are produced in a nearby area and therefore, the

transportation distance to the MED unit was set to 200 km, and the same distance was assumed for landfilling. The biomass pellets are produced in Bío Bío Region, Southern Chile (2,500 km distance from Taltape). To enable a fair comparison of transportation requirements to the MED unit, the diesel used for electricity generation was assumed being transported from one of the main oil suppliers to Chile, the Neuquén region in Argentina, thus at 3,000 km from Taltape (Gaete-Morales et al., 2018).

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Table 1 - Life cycle inventory of the energy supply of the Taltape MED plant and its alternatives (for the MED unit inventory see Table S2 in the supporting information). Values per functional unit.

COS Option A Option B Option C

Infrastructure

Diesel generator set (g)a 11.6 5.8 - -

Biomass boiler (g)a 6.8 3.4 6.8 3.4

Solar thermal field

Copper (g)b - 1.7 - 1.7

Glass tube, borosilicate (g)c - 2.0 - 2.0

Propylene glycol, 15% (heat transfer media) (g) - 0.3 - 0.3

Inert landfill (g) 4.0 4.0

Photovoltaic solar fieldPhotovoltaic panel, multi-Si (m2) - 2.15E-4 - 2.15E-4

Batteries, lithium (g) - 2.7 - 2.7

Plant operation

Consumables

Sodium phosphate (anti-crusting) (g) 80 80 80 80

Sulfuric acid (cleaning agent) (mg) 1.36 1.36 1.36 1.36

Lubricating oila (generator set) (g) 19.6 9.8 - -

Diesel (kg) d 7.29 3.65 - -

Wood pellets (kg)21.9

810.99 21.98 10.99

Chilean grid, low voltage (kWh)e - - 28.57 14.29

Transport

Road transportf

Diesel (t.km)e 21.87

10.95 - -

Biomass pellets (t.km)54.9

5 27.48 54.95 27.48

Other consumables (t.km) 0.02 0.02 0.02 0.02a Amount estimated from the Ecoinvent databaseb Includes drawing of pipec Density 2.23 g/cm3

d Density 0.832 kg/Le Includes grid infrastructuref Euro5: lorry 16-32 tonne

2.3. Impact assessment

The software Gabi 8.0 (Thinkstep, 2015) was used for LCA modelling and impact estimation. The ReCiPe 1.08 method (Huijbregts et al., 2017) hierarchical perspective was applied to estimate the potential environmental impacts, considering the following 13 mid-point impact categories: climate change potential (CCP), fossil fuels depletion (FDP), metals depletion potential (MDP), ozone depletion potential (ODP), photochemical oxidant formation (POFP), particular matter formation potential (PMFP), freshwater eutrophication potential (FEP), marine eutrophication potential (MEP), freshwater ecotoxicity potential (FETP), marine ecotoxicity potential (METP), terrestrial ecotoxicity potential (TETP), human toxicity potential (HTP) and terrestrial acidification potential (TAP).

3. Results

In the next sections, the obtained results for the ReCiPe method are discussed. This is followed by comments on the environmental hotspots and sensitivity analysis of diesel and biomass transportation distances.

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3.1. Life cycle environmental impacts

The impact results for the COS and options A, B and C are shown in Figure 2 (for results in contribution percentages see Figure S1 in the supporting information). The results demonstrate that the COS (i.e. diesel generator set and biomass boiler) of the MED unit has the highest impacts in nine out of 13 impact categories. Option C (Chilean grid electricity, biomass boiler and solar fields) have the lowest impacts in nine categories (option A in other four) while option B does not score as the best in any category. The MED subsystem contributed to less than 7% to the environmental impacts and transportation of anti-crust and cleaning agents have combined contributions of less than 4%. These results are discussed in detail below.

3.1.1. Climate change potential (CCP)The climate change potential of the COS of the Taltape MED unit is estimated at 47.0 kg CO2-

eq./FU. 57% of the total is due to emissions from the electricity generator (25.9 kg only from CO2

emissions to air) and 18% from transportation of diesel and biomass pellets to the facility. Option C, the best in this category, has a total impact of 16.9 kg CO2-eq./FU - 28% from transportation of biomass pellets and 50% from emissions associated with the grid electricity generation (Figure 2). Options A and B are intermediate for CCP, with 23.7 kg CO2-eq./FU and 33.3 kg CO2-eq./FU, respectively. For Option A, 56% of the impact is originated from diesel combustion in the electricity generator and 19% from transportation of biomass pellets; for Option B the combination of biomass boiler and grid electricity is responsible for 72% of the total.

3.1.2. Resources depletion potentials (FDP and MDP)The same pattern in CCP was observed for fossil depletion potential. Option C has again the

lowest impact (4.8 kg oil-eq./FU) followed by option A (7.8 kg oil-eq./FU). Option B has nearly the double of the impact estimate for option C, with 9.4 kg oil-eq./FU. The impact of the COS is the highest (15.5 kg oil-eq./FU), with a contribution of 58% from diesel generator set (of which 8.4 kg from crude oil depletion) and nearly 30% from transportation of diesel and biomass pellets. In options B and C, impacts are mainly from transportation of biomass pellets (25%) and grid electricity (55%), mostly from coal and crude oil depletion.

The metal depletion potential of the COS is also the highest, with 1.35 kg Fe-eq./FU. In options A and C, the use of PVs and ETCs are responsible for 8%-12% of the total impact each, mostly due to the depletion of chromium, molybdenum and nickel. The infrastructure for the MED subsystem (see Figure 1 and Table S2) has contributions of 3-7%, the highest among all categories. The best option for MDP is option C, with 0.69 kg Fe-eq./FU, which has most of its impacts (~50%) arising from the transportation and combustion of biomass pellets (depletions of iron, manganese and copper).

3.1.3. Air impacts (ODP, POFP and PMFP)For ozone depletion potential the results indicate the COS has twice the impacts of the options

A and almost 6 times more than option C, with a result of 7.6 mg CFC-11-eq./FU. Combustion of diesel for energy production and transportation contributes to more than 90% of the impacts in this option, almost entirely from emissions of Halon 1301 to air. The COS has the worst results for

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photochemical oxidant formation potential, 7.4 times higher than option C, which is the best in this category (0.59 kg and 0.08 kg NMVOC/FU). The impacts of the COS are mainly originated (80%) from NOx emissions to air from diesel combustion in the electricity generator set. For option C, 40% of the impact is generated from pellets burning in the boiler and 31% from grid electricity – in both cases the emission to air of NOx is the most significant contributor. In particular matter formation potential, the options A and B have intermediate results (0.11 kg and 0.09 kg PM10-eq./FU respectively). Option C is the best in this category (0.04 kg PM10-eq./FU) and has an impact 5.8 times lower than the COS (0.23 kg PM10-eq./FU). Diesel combustion in the electricity generator set for the COS is the major contributor (69%) due to emissions of NOx and, to a lesser extent, of SO2.

3.1.4. Eutrophication potentials (FEP and MEP)Option B has the highest freshwater eutrophication potential, with 10.9 g P-eq./FU. From this

total, 3.7 g P-eq. are from phosphates originating from the biomass combustion emissions to air and 6.6 g P-eq. from the generation of grid electricity, mainly associated with the mining of coal. This result is two times higher than the COS and option C (5.9 g P-eq. in both cases). Option A has the lowest results, with a total of 3.6 g P-eq./FU. Air emissions from biomass burning and generation of grid electricity are major contributors (>55%) to this category. Option C has the lowest impact in marine eutrophication potential (4.6 g N-eq./FU), 5.1 times lower than the COS and 2.6 times lower than option A (23.4 g and 11.8 g N-eq.). The impacts from the COS are 71% from NOx emissions to air from diesel combustion in the electricity generator set and approximately 19% from biomass boiler emitting NH3, NOx and NO3

-.

3.1.5. Ecotoxicity potentials – freshwater, marine and terrestrial (FETP, METP and TETP)Option B performs worst for freshwater and marine ecotoxicity potentials (1.49 kg and 1.29 kg

1,4-DB-eq./FU), being slightly higher than the COS (1.33 kg and 1.15 kg 1,4-DB-eq./FU for FETP and METP, respectively). The main contributor, with over 45% in these two categories, is biomass burning (mostly from the emission of zinc to air). Options A and C also had fairly similar results in these two categories, with PVs and ETCs accounting for 2% each to the total impact, while the MED unit to about 1%. For terrestrial ecotoxicity the COS and option B have similar results, of 76.4 g and 74.7 g 1,4-DB-eq./FU; the impacts of options A and C are approximately 50% lower. The emission of phosphorus from the biomass boiler to agricultural soil is responsible for 90% of the total impact in this category for all energy supplies assessed.

3.1.6. Human toxicity potential (HTP)Options A and C had the lowest and nearly equivalent results for human toxicity, with 11.9 kg

and 12.7 kg 1,4-DB-eq./FU, respectively. Option B was the worst in this category, with an estimated impact of 23.5 kg 1,4-DB-eq./FU. For COS and the three energy supply alternatives, 65% of the impact is from biomass combustion emitting magnesium and zinc to the air.

3.1.7. Terrestrial acidification potential (TAP)The COS has the highest results for terrestrial acidification (0.38 kg SO2 eq./FU), twice the

impact of option A with 0.19 kg SO2 eq./FU, which is the second worst performing. For both, nearly 75% of the total derives from the NOx emission from diesel combustion in the electricity generator set. The total impact for the COS is 4.6 times the impact of option C, the best in this category. For options

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B and C, grid electricity emissions correspond to about half of the impacts, followed by biomass boiler with 30 % - mostly from air emissions of SO2, NOx and NH3.

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CCP[kg CO2-eq.]

FDP[kg oil-eq.]

MDP[kg Fe-eq. x 0.1]

ODP[mg CFC-11-eq.]

POFP[kg NMVOC x

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x0.01]

FEP[g P-eq.]

MEP[g N-eq.]

FETP[kg 1,4-DB-eq.

x0.1]

METP[kg 1,4-DB-eq.

x0.1]

TETP[g 1,4-DB-eq.]

HTP[kg 1,4-DB-eq.]

TAP[kg SO2-eq.

x0.01]

MED unit Electricity (generator set) Transport (diesel)

Electricity (PVs) Heat (ETCs) Other consumables

Electricity (Chilean grid) Heat (biomass boiler) Transport (pellets)

Figure 2 – Life cycle environmental impacts of the Taltape MED plant and different options for its energy supply. COS: Current operating strategy. PVs: photovoltaic panels; ETCs: evacuated solar tube collectors. COS and energy supply strategies (Options A, B and C) defined in section 2.1.2. The values shown on top of should be multiplied by the factor shown in brackets for some impacts to obtain the original values. CCP: climate change potential; FDP: fossil fuels depletion: MDP: metals depletion potential; ODP: ozone depletion potential; IRP: ionizing radiation potential; POFP: photochemical oxidants formation; PMFP: particular matter formation potential; FEP: freshwater eutrophication potential; MEP: marine eutrophication potential; FETP: freshwater ecotoxicity potential; METP: marine ecotoxicity potential; TETP: terrestrial ecotoxicity potential; HTP: human toxicity potential; TAP: terrestrial acidification potential. Results per functional unit.

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3.2. Sensitivity analysis on biomass and diesel transportation distances

Given that the transportation of diesel and biomass pellets were found to have significant contributions to several impact categories, a sensitivity analysis was carried out to investigate how variations in distance would reflect on the environment impacts. The obtained results are shown in Figure 3, demonstrating that the contribution of diesel transportation (only used for the COS and option A – see Table 1) to impacts are significantly lower than from biomass pellets. It can also be observed from Figure 3 that decreasing biomass pellets and diesel transportation distances would not make either the COS or option A more attractive in terms of environmental impacts in comparison with options B and C.

0

10

20

30

40

50

60

70

80

CCP(kg CO2-eq.]

FDP[kg oil-eq.]

MDP[kg Fe-eq. x

0.1]

ODP[mg CFC-

11-eq.]

POFP[kg NMVOC

x 0.01]

PMFP[kg PM10-eq. x0.01]

FEP[g P-eq.]

MEP[g N-eq.]

FETP[kg 1,4-DB-

eq. x0.1]

METP[kg 1,4-DB-

eq. x0.1]

TETP[g 1,4-DB-

eq.]

HTP[kg 1,4-DB-

eq.]

TAP[kg SO2-eq.

x0.01]

COS (biomass distance variation) COS (diesel distance variation)

Option A (biomass distance variation) Option A (diesel distance variation)

Option B (biomass distance variation) Option C (biomass distance variation)

Figure 3 - Sensitivity analysis of transportation distances in the life cycle environmental impacts of the Taltape multi-effect distillation plant and different options for its energy supply. Uncertainty bars represent variations in transportation distances - 3,000 km to 0 km for diesel and 2,500 km to 0 km for biomass pellets. Current operating strategy (COS) and energy supply strategies (Options A, B and C) defined in section 2.1.2. For impacts nomenclature see Figure 2. Results per functional unit.

4. Discussion

The amount of desalinated water keeps growing worldwide and this trend is expected to continue in the coming years to cope with growing urban and agricultural water demands (Burn et al., 2015; Mezher et al., 2011). This means that environmental impacts coming from this activity are also likely to increase. In large-scale plants located in Spain, a previous evaluation indicated the use of solar-based energy for MED could reach CO2-eq. emissions as low as 8.2 kg per m3 of desalinated seawater (Raluy et al., 2005), value this half of the obtained in this paper (minimum 16.9 kg CO2-eq.) for the same amount of water. This can be

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explained by the contribution of biomass transportation to the Taltape as well as different electricity grid contributions and plant dimensions.

The results of this paper indicate that for a small MED plant located in northern Chile the combustion of diesel for electricity generation onsite is contributing more than 50% to seven impact categories (CCP, FDP, ODP, POFP, PMFP, MEP and TAP) for the COS and option A. For options B and C, grid electricity plays a major role (> 40%) in four4 categories (CCP, FDP, FEP and TAP) and biomass boiler in other seven (POFP, PMFP, MEP, FETP, METP, TETP and HTP). Regarding the biomass boiler, a caveat about the substitution of the Ecoinvent process (see section 2.2) is necessary. Firstly, the emission of particles is dependant on the burning condition, fuel and type of boiler (Obaidullah and Bram, 2012). Secondly, the emission of metals is also dependant on their concentration in wood pellets, which can vary with different origins of the biomass (Chandrasekaran et al., 2012). Thus, there is high uncertainty regarding the biomass particle and metals emissions during the burning and their contribution to particulate matter and human and eco-toxicity impacts.

The transportation of biomass and diesel to the Taltape MED plant have significant to high contributions (from 10% up to 70%) across all impact categories (consult Figure S1 in the supporting information). The unfavourable environmental outcome of using biomass in desalination has already been suggested in literature, observing that its use for desalination is not a desirable alternative since organic residues are not readily available in arid regions (Eltawil et al., 2009). The decreasing in diesel and biomass pellet consumption and, therefore the transport associated, are the main reasons for the lowered impacts when coupling solar fields and grid electricity in MED process. Hence, when evaluating potential locations for implementing desalination plants, it is wise to assess transportation distances of the main consumables besides variations in operating strategies. The use of multi-criteria analysis seems to be appropriate for such type of assessment (Dweiri et al., 2018; Zanghelini et al., 2018).

4.1. Distilated water quality

As illustrated in Table 2, the water from the Camarones River supplying the MED plant in the Taltape community does not comply with the minimum regulated values for irrigation water and livestock drinking as the concentrations of As, B, sulfates, chlorides and other substances are higher than current guidelines. However, the MED process removes more than 92% of the metal content, total dissolved solids, sulfate and chlorine ions present in the Camarones River. More specifically in relation to As and B, the MED treatment removed 99% (final concentration 0.006 mg/L) of the As and 96% (final concentration 0.57 mg/L) of the B. Therefore, the distillate water obtained from the MED plant can be considered of high quality, complying with values required for use in irrigation (As 0.10 mg/L and B 0.75 mg/L) and livestock drinking (As 0.05 mg/L and B 1.00 mg/L) (INN, 1987) and whose characteristics can be easily modified to include adequate salt concentrations. Finally, the stream returned to the Camarones River (spill) is similar in composition to the feed stream, with slight increases of 1.0%-2.0% in the average measured concentrations.

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Table 2 – Flows and parameters of the water in the Taltape multi-effect distillation (MED) plant and permissible concentrations by the Chilean regulations for water use for irrigation and livestock drink

UnitMED unit feed

(Camarones River)Effluent

(Distillate water)Brine

(MED effluent)Spill

(Return water)

Irrigationstandard

s(INN, 1987)

Livestock drink

Standards (INN, 1987)

Minimum Average Maximum

Flow m3/h 24.3 0.42 0.38 23.38 - -

Total dissolved solids

mg/L1,600 1,900 2,100

19.50 4,100 1,985500 500

Conductivity µS/cm 2,500 2,600 2,900 200 5,040 2,541 750 750

Arsenic (Astotal) mg/L 0.10 0.60 0.95 0.006 1.30 0.61 0.10 0.05

Boron (Btotal) mg/L 11.30 15.00 26.7 0.57 23.20 11.50 0.75 1.00

Cadmium (Cd+2) mg/L 0.005 0.050 0.090 0.004 0.10 0.05 0.01 0.05

Calcium (Ca+2) mg/L 120 210 250 4.80 250 122 - -

Chlorides (Cl-) mg/L 680 700 1,200 47.70 1,390 692 200 100

Iron (Fetotal) mg/L 0.05 0.20 0.42 0.004 0.10 0.05 0.30 0.30

Manganese (Mn+2) mg/L 0.05 0.13 0.30 0.001 0.10 0.05 0.20 0.05

Lead (Pb+2) mg/L 0.02 0.03 0.04 0.002 0.04 0.02 0.20 0.05

Potassium (K+) mg/L 6.2 35.0 50.0 0.30 12.70 6.30 - -

Sodium (Na+) mg/L 330 450 670 3.30 690 336 - -

Sulfate (SO42-) mg/L 220 310 420 22.20 565 285 250 120

As the final distillate water available to the Taltape community contains metals and metalloids in levels below those required by Chilean regulations for safe use in agricultural purposes, the results suggest that the MED treatment of brackish water using solar energy is an environmentally viable alternative for improving the availability of fresh water to the Taltape inhabitants. Currently, the Regional Government of Arica & Parinacota in Chile is financing projects to develop more MED plants in the rural areas of the region, establishing thermal desalination technologies as a potential solution to solve water scarcity issues. Despite the promising technical results regarding the obtained distillate quality, the sustainable use of its limited output must be prioritized. In this sense, a business model was developed in the Taltape community to promote an efficient use of the distillate. The production of premium cheese, gerbera daisy flowers and strawberry emerged as the most desirable options as these agricultural products complied with the main goal of the initiative which are: i) moderate water consumption; ii) high value-added production; and iii) sufficient

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technical knowledge of the population. Touristic incentives are under consideration since local hotels and restaurants can now be certified.

5. Conclusions

This paper assessed the environmental implications of substituting the current energy supply of a small MED plant, located in an isolated community in Northern Chile, from diesel and biomass to solar and grid electricity. Based on the findings, it can be argued that the Taltape MED plant would benefit, from the environmental standpoint, more from the decreasing of the use of biomass pellets than from closer sources of biomass - suggesting the adoption of solar energy is the most environmentally beneficial alternative. Moreover, it can be concluded that the use of grid electricity would also act to the decrease the impacts of the Taltape MED plant, but to a lesser extent. The plant was also effective in removing As and B found in the Camarones river to limits below required by Chilean regulations, enabling the use of the distillate to agricultural purposes to the Taltape community. The use of solar energy for MED treatment of brackish water in isolated and deserted communities can be considered an environmentally suitable alternative to cope with fresh water scarcity around the world.

AcknowledgmentsThis research has been funded by the Arica & Parinacota Regional Government

(Fondo de Innovación para la Competitividad: Taltape, BIP code 30158422-0). PhD. Sara Miralles-Cuevas wishes to thank the Solar Energy Research Center for her post-doctoral position in Arica, Chile, under SERC-Chile, FONDAP project (reference: 15110019). PhD. Alejandro Cabrera wishes to thank his post-doctoral position at University of Tarapacá. The authors will like to thank Carlos Gaete-Morales for his contributions to calculate the impacts associated to the Chilean electricity mix.

Supplementary dataThe supporting information includes data on the electricity mix in Chile in 2014, the

life cycle inventory of the multi-effect distillation (MED) subsystem and the impacts percentages breakdown of the Taltape MED plant and different options for its energy supply.

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Environmental assessment of sustainable energy options for multi-effect distillation of brackish water in isolated communities

Raphael Ricardo Zepon Tarpani, Sara Miralles-Cuevas, Alejandro Gallego-Schmid, Alejandro Cabrera-Reina A, Lorena Cornejo-Ponce

Supporting information

This supporting information includes data on the electricity mix in Chile in 2014 (Table S1 in page S2), the life cycle inventory of the multi-effect distillation (MED) subsystem (Table S2 in page S2) and the impacts percentages breakdown of the Taltape MED plant and different options for its energy supply (Figure S1 in page S3).

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Table S1. Electricity mix in Chile in 2014 (Gaete-Morales et al., 2018)Source Contribution

Coal 41.4%

Hydro 33.7%

Natural gas

14.3%

Oil 3.9%

Biomass 3.9%

Wind 2.0%

Solar 0.7%

Table S2. Life cycle inventory of the multi-effect distillation (MED) subsystem infrastructure.

Infrastructure Ecoinvent process Values per FU Total weight Unit

Sand filter

Silica sand (filter media) GLO: silica sand production 0.00136 100.07 kgPolyvinyl chloride (pipes and valves) GLO: polyvinylchloride production, bulk polymerization 0.00013 9.57 kgChromium steela (pipe clamping frame) GLO: steel, chromium steel 18/8, hot rolled 0.00020 14.72 kg

Anti-fouling dispenser

High density polyethylene (tank) GLO: polyethylene production, high density, granulate 0.00007 5.15 kgPolypropylene (sensor, dosage pump and pump body) GLO: polypropylene production, granulate 0.00004 2.94 kgPolyvinyl chloride (valves) GLO: polyvinylchloride production, bulk polymerization 0.00001 0.74 kgPolyvinyl fluoride (valves and dosage pump) GLO: polyvinyl fluoride production 0.00001 0.74 kgTetrafluoroethylene (diaphragm) GLO: tetrafluoroethylene production 1.4E-06 0.10 kg

Brackish water tank

Polypropylene (tank) GLO: polypropylene production, granulate 0.00095 69.90 kgPolyphenylene sulfide (level sensor) GLO: polyphenylene sulfide production 0.00001 0.74 kgPolyvinyl chloride (valves) GLO: polyvinylchloride production, bulk polymerization 0.00009 6.62 kgChromium steela (vacuum pump) GLO: steel, chromium steel 18/8, hot rolled 0.00014 10.30 kg

Multi-effect distillation

Chromium steela (effects, condensator and valve actuator) GLO: steel, chromium steel 18/8, hot rolled 0.00836 615.16 kgPolyphenylene sulfide (level sensor) GLO: polyphenylene sulfide production 0.00001 0.74 kgPolypropylene (valves, valves actuators and water meter) GLO: polypropylene production, granulate 0.00005 3.68 kgPolypropylene (control block) GLO: polypropylene production, granulate 2.0E-06 0.15 kg

Distillate water tank

Polypropylene (lung) GLO: polypropylene production, granulate 0.00095 69.90 kgHigh density polyethylene (distilled water tank) GLO: polyethylene production, high density, granulate 0.00059 43.41 kgPolyphenylene sulfide (level sensor) GLO: polyphenylene sulfide production 0.00001 0.74 kgPolypropylene (level sensor) GLO: polypropylene production, granulate 0.00005 3.68 kgPolypropylene (valves, valves actuators and water meter) GLO: polypropylene production, granulate 0.00020 14.72 kgPolypropylene (control block) GLO: polypropylene production, granulate 2.0E-06 0.15 kgChromium steela (vacuum pump) GLO: steel, chromium steel 18/8, hot rolled 0.00014 10.30 kg

Other equipment

Polypropylene (tanks) GLO: polypropylene production, granulate 0.00204 150.11 kgChromium steela (heat exchanger and heat pump) GLO: steel, chromium steel 18/8, hot rolled 0.00048 35.32 kgChromium steela (centrifugal pumps) GLO: steel, chromium steel 18/8, hot rolled 0.00029 21.34 kgCopperb (pipes) GLO: copper production, primary 0.00008 5.89 kgPolyvinyl chloride (valves) GLO: polyvinylchloride production, bulk polymerization 0.00003 2.21 kg

DecommissioningInert landfill CH: disposal, inert waste, 5% water, to inert material landfill 0.01630 1199.08 kga Includes metal working machineb Includes drawing of pipe

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CCP[kg CO2-eq.]

FDP[kg oil-eq.]

MDP[kg Fe-eq. x 0.1]

ODP[mg CFC-11-eq.]

POFP[kg NMVOC x

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PMFP[kg PM10-eq.

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FEP[g P-eq.]

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FETP[kg 1,4-DB-eq.

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METP[kg 1,4-DB-eq.

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TETP[g 1,4-DB-eq.]

HTP[kg 1,4-DB-eq.]

TAP[kg SO2-eq. x0.01]

MED unit Heat (ETCs) Electricity (PVs) Electricity (generator set) Electricity (Chilean grid)Transport (diesel) Other consumables Heat (biomass boiler) Transport (pellets)

Figure S1. Environmental impacts of the Taltape MED plant and different options for its energy supply. PVs: photovoltaic panels; ETCs: evacuated solar tube collectors. Current operating strategy (COS) and energy supply strategies (Options A, B and C) are defined in section 2.1.2 of the main article. CCP: climate change potential; FDP: fossil fuels depletion: MDP: metals depletion potential; ODP: ozone depletion potential; IRP: ionizing radiation potential; POFP: photochemical oxidants formation; PMFP: particular matter formation potential; FEP: freshwater eutrophication potential; MEP: marine eutrophication potential; FETP: freshwater ecotoxicity potential; METP: marine ecotoxicity potential; TETP: terrestrial ecotoxicity potential; HTP: human toxicity potential; TAP: terrestrial acidification potential.

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ReferencesGaete-Morales, C., Gallego-Schmid, A., Stamford, L., Azapagic, A., 2018. Assessing the environmental sustainability of electricity generation in Chile. Sci. Total Environ. 636, 1155–1170. doi.org/10.1016/j.scitotenv.2018.04.346

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