Arsenic Removal from Natural Waters by Adsorption or Ion Exchange: An Environmental Sustainability Assessment

Arsenic Removal from Natural Waters by Adsorption or IonExchange: An Environmental Sustainability AssessmentAntonio Dominguez-Ramos,† Karan Chavan,‡ Veronica García,† Guillermo Jimeno,⊥ Jonathan Albo,∥

Kumudini V. Marathe,‡ Ganapati D. Yadav,‡ and Angel Irabien*,†

†Departmento de Ingenierías Quimica y Biomolecular, Universidad de Cantabria, Avda de los Castros, s.n., 39005 Santander, Spain‡Department of Chemical Engineering, Institute of Chemical Technology, Nathalal Parekh Marg, Matunga, Mumbai 400019, India∥Departmento de Ingeniería Química, Universidad del País Vasco, Apdo. 644, 48080 Bilbao, Spain⊥Centre for Oscillatory Baffled Reactor Applications, School of Engineering and Physical Science, Chemical Engineering, Heriot-WattUniversity, Edinburgh, Riccarton EH14 4AS, United Kingdom

*S Supporting Information

ABSTRACT: The Environmental Sustainability Assessment of the adsorption and ion-exchange processes for arsenic removalwas the focus of this work. The pursued goals were to determine the impact of regenerating the activated alumina used asadsorbent and the comparison of the environmental performance of two ion-exchange resins. Additional goals were thecomparison between the environmental performance of adsorption and ion-exchange processes and the evaluation of the effect ofintegrating the proposed techniques on a water purification facility. The Life Cycle Inventory was obtained by means ofsimplified models and simulation. In this work it was concluded that the removal of As(V) by adsorption consumed between 2and 13 times more primary resources and created 3−17 times more environmental burdens than the ion-exchange process. Theintegration of adsorption or ion-exchange technology in the drinking water plant would raise the primary consumption of energy,materials, and water by 27−155%, 7−94%, and 0.48−5.3%, respectively. The increase in the environmental burdens was mainlybecause of the generation of hazardous spent materials.

■ INTRODUCTION

Excessive quantities of arsenic (As) in drinking water1,2 inSpain3−5 and India6−9 are well documented. The problem ismore acute in India, where as many as 60 million people are atrisk of chronic As poisoning.10 The World Health Organizationhas established 10 μg As·L−1 as the safety standard for Asconcentrations in drinking water.11 This value was endorsed by theEuropean Union12 and by the Bureau of Indian Standards.13

In order to remove As from water for drinking purposes,enhanced treatment processes are needed14 due to thelimitations of conventional treatments.15 A broad range ofenhanced As removal techniques are reported in the literature:oxidation/precipitation,16,17 coagulation/electrocoagulation/coprecipitation,18−20 membrane technologies,21−23 adsorp-tion,15,24−26 photocatalysis,27 biosand filters,28 and ion-exchange.29

Among the mentioned technologies, adsorption is considered theless expensive procedure and safer to handle than precipitation,ion-exchange, and membrane filtration.15 Adsorption is simple inoperation, and it is used at different scales, ranging from householdmodules to community plants.30−32 However, the adsorbent can beregenerated few times. On the other hand, ion-exchange is anothereffective technique for As removal, which tolerates a larger numberof regeneration cycles.30

Research regarding the technical performance of adsorptionand ion-exchange for As removal is abundant, and many reviewsare being published.14,33−38 However, the environmentalperspective is not usually considered.39 The life cycle approachcan be adopted to evaluate the Environmental SustainabilityAssessment (ESA) of products, processes, or services.40

The present study focuses on the ESA of adsorption and ion-exchange processes for As removal within a drinking watertreatment plant using Life Cycle Assessment. The ESA of theadsorption process was conducted considering activated alumina(AA) as it is the most common industrial adsorbent.15,30 The ESAof the ion-exchange process considered the use of commercial andunder-development selective ion-exchange resins. The usedresources and the environmental burdens generated by the twoprocesses during the Cradle-to-Gate and Gate-to-Gate steps wereaccounted. The effect of the regeneration of the AA and the typeof resins were considered. Additionally both technologies werecompared.

■ METHODOLOGY

Goal and Scope. The study compares the removal of Asfrom natural waters using adsorption or ion-exchange processeswithin a drinking water treatment plant. The main objectivewas to quantify the ESA of the adsorption and ion-exchangeprocesses and to compare both options. Additional goals wereto determine the impact of regenerating the used AA as well asthe utilization of two types of resins.

Special Issue: Ganapati D. Yadav Festschrift

Received: December 30, 2013Revised: February 6, 2014Accepted: February 15, 2014Published: February 16, 2014

Article

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© 2014 American Chemical Society 18920 dx.doi.org/10.1021/ie4044345 | Ind. Eng. Chem. Res. 2014, 53, 18920−18927

pubs.acs.org/IECR

The scope of the assessment was based on the integration ofthe As removal process into a medium-sized drinking watertreatment plant of continuous flow rate of 1.38 × 106 m3·year−1.Regarding the source, i.e., surface water or groundwater,different specific pretreatments could be required. However,this work was focused on the concentration of As in the rawwater and not on the source of the drinking water.Consequently a general intensive physical and chemicalpretreatment process was considered: precipitation/oxidation,coagulation/flocculation/sedimentation, filtration, and disinfec-tion. Figure 1 depicts the raw materials acquisition and the

operation process for the removal of As in a drinking watertreatment plant. The raw water could be directly diverted to theplant or to intermediate processing as a natural resource. Theinlet concentration for the As removal process was set up at 100ppb: the maximum level of As that raw water could contain inorder to be treated for drinking purposes under the Spanishregulation.41 The composition of the inlet water was modeledas exclusively of As(V); thus, the presence of other competingions was not considered for the sake of simplicity. The safetyvalue of 10 ppb was considered as the outlet concentration levelfor the As removal process. In this work, the focus was made onthe removal of As; thus, the pretreatment or further disinfectionwas not modeled. Consequently, the adsorption and the ion-exchange steps were analyzed, modeled, and simulated in detail.The functional unit in this work was 1 m3 of treated water.Within the scope of the work, the study considered the Cradle-to-Gate approach (Figure 2):Cradle-to-Gate (C-G): The environmental burdens gener-

ated by the transformation of natural/primary resources intousable forms of resources. This step included all individualtransformation processes such as raw materials extraction,manufacturing, transportation, etc. The natural resourcesincluded the primary form of energy, materials, water, andland, whereas the final resources were sorbent or resins,electricity, water, and regeneration reagents.Gate to Gate (G-G): the environmental burdens generated

by the transformation of final resources into a product, aprocess, or a service. In this study, G-G step referred to the

adsorption or the ion-exchange process. The environmentalburdens originated from the release of the removed As to waterbodies and spent adsorbent/resin to land. There were noemissions to air.The treatment of the liquid and solid wastes from the As

removal step, i.e., the Gate-to-Grave step, was out of the scopeof this work. This was due to the large uncertainty of thepotential waste management options. Land usage was alsoexcluded in this study, as the alternatives are expected toprovide similar values for this resource. Therefore, the twosteps within the Cradle-to-Gate analysis shown in Figure 1 (rawmaterial acquisition and operation) are clearly identified withthe steps depicted in Figure 2 as C-G and G-G.

Description of Systems under Study. Two differentAs(V) removal processes were considered, leading to fourscenarios as shown in Figure 3: the first two included the use ofAA adsorption for As removal, and the last two regarded theutilization of ion-exchange. In order to weigh the resources andburdens generated by the removal processes within aconventional drinking water treatment plant, a fifth referencescenario was added. A brief description of each scenario isprovided below, specific features of each scenario are providedin the Supporting Information (SI):

• Scenario ADS: the removal of As using AA. Noregeneration step was considered, and the spent AAcontaining the retained As became hazardous waste.

• Scenario ADS-R: Drinking water treatment by AAincluding its regeneration utilizing chemicals. The AAbecame hazardous waste after a certain number ofregenerations steps. Each regeneration cycle caused a lossin the removal capacity of AA. The cleaning solution wasreleased to the water compartment.

• Scenario IEX-R: the use of commercial resin LewatitFO36 for drinking water treatment. This scenarioconsidered the resin regeneration without any efficiencyloss. The cleaning solution was released to the watercompartment. Once the resin reached its lifetime, it wasdiscarded as hazardous waste.

• Scenario SIEX-R: the removal of As using a selective labresin based on an iron(III) cover which included theregeneration step without any efficiency loss. Similar toscenario IEX-R, the selective resin was discarded ashazardous waste after use and the cleaning solutionreleased to seawater. The regeneration procedure wasdifferent than the regeneration used in scenario IEX-R.

• Scenario DW: this scenario regarded the pretreatment ofthe water prior to the As removal. It was based on aconventional water purification facility. It is assumed thatno As is removed in this step.

The adsorption was modeled assuming that the solid−liquidequilibrium was attained in a fixed bed configuration; theremoval of As(V) was in continuous mode until the bed wasfully saturated.

Life Cycle Inventory. In order to compare the environ-mental sustainability of the processes, the adsorption and theion-exchange stages were simulated. As a result of thesimulation, the Life Cycle Inventory (LCI) was estimated foreach scenario by means of the amount of final resources andpollutants for the calculation of the Natural ResourcesSustainability (NRS) and of the Environmental BurdensSustainability (EBS), respectively. The same procedure wasused for the analysis, modeling and simulation of the four

Figure 1. Block diagram of the C-G analysis of the system under study.

Industrial & Engineering Chemistry Research Article

dx.doi.org/10.1021/ie4044345 | Ind. Eng. Chem. Res. 2014, 53, 18920−1892718921

simulated scenarios in order to obtain the resources used in theG-G step: the amount of adsorbent or resin, the electricityneeded for overcoming the pressure drop, the rinsing water,and the products and water used in the regeneration process(Figure 2). Further, two wastes were generated: the spentsorbent or resin and a liquid effluent that contained As(V).

This liquid waste was produced as a result of each regenerationstep. Full details of the simulation carried out are providedin the SI along with the selected parameters.The LCI referred to the results of this simulation as shown in

Figure 3. It is important to note that the results presented inthe LCI depended on the used parameters, and the selected

Figure 2. Block diagram of the Life Cycle Environmental Sustainability Assessment. NRS: Natural Resources Sustainability, EBS: EnvironmentalBurdens Sustainability, LCESA: Life Cycle Environmental Sustainability Assessment.

Figure 3. Block diagram of the removal of As by the adsorption or ion-exchange processes in a drinking water treatment plant. F: flow rate incomingto the As removal step, C0: inlet concentration of As, Ce: outlet concentration of As. ADS: adsorption of AA without regeneration; ADS-R:adsorption of AA with regeneration; DW: pretreatment of water prior to the As removal; IEX-R: ion-exchange using commercial resin andconducting a regeneration step; SIEX-R: ion-exchange using lab resin and conducting a regeneration step.



model. Regarding the technical performance, the scenario ADS-R treated a total volume of around 27,000 BV during the fiveregeneration cycles, which was equivalent to a lifetime of 95 days.This value was lower than the 10,000 BV of AA per cycle reportedby US-EPA.42 Therefore the value of the adsorption capacity qeused in this work directly affected the number of BV that could betreated, i.e., changing the number of BV is equivalent to alteringthe total treated volume of water VT which in turn modifies the lifecycle inventory. Around 210,000 BV were treated with theconsidered resins.Once the simulations of the different scenarios were

completed, the emissions to air, effluents, and solid wasteswere transformed into EBS values by means of GaBi LCA v4.3software.43 For the upstream processes, the Ecoinvent data-base44 was used as reference considering European data(Spanish grid mix for electricity consumption, cationic resinfor the resins, and aluminum oxide for the AA).Regarding the selected metrics for conducting the EBS of the

five scenarios, the IChemE metrics for Process Industriesproposed in “The Sustainability Metrics”45 were considered.These metrics expressed the environmental sustainability ofemissions, effluents, and wastes from the treatment scenarios. Aweighting procedure was conducted according to the EuropeanPollution Release and Transfer Register to obtain dimensionlessnormalized environmental burdens as described elsewhere.46

■ RESULTS AND DISCUSSION

The main LCI results for the removal of As by adsorption aresummarized in Table 1. According to the results of thesimulation, conducting the regeneration step did not affect theamount of electricity used during the treatment process. Thiswas due to the assumption of equal pressure drop for eachscenario and that the electricity used in the regeneration stepwas negligible compared to the former. Regarding theconsumption of materials, the scenario ADS used about5 times more adsorbent to treat 1 m3 of water than scenarioADS-R due to the lack of regeneration. However, theregeneration process entailed a large consumption of chemicalreagents, up to 0.56 kg·m−3. Thus, there was a clear trade-offbetween the usage of AA and regeneration reagents. Finally, the

scenario ADS did not need water for the regeneration asopposite to scenario ADS-R.The LCI also indicated that resource usage for the scenarios

IEX-R and SIEX-R was similar in terms of energy and water.Concerning the material consumption, Table 1 shows thatcomparable quantities of the two resins were needed. This wasdue to the similar values of the qe and the lifetime LT in bothscenarios. However, the regeneration procedure affected theamount of final materials used, and almost 3 times more finalmaterials were needed in scenario IEX-R. Consequently,scenario SIEX-R was preferable from the resource usageperspective.The comparison of the material usage among the scenarios

ADS, ADS-R, and SIEX-R showed that the removal of As fromraw water by means of ion-exchange reduced the amount ofadsorbent needed. The observed decrease was from 0.119 kg·m−3

in ADS and 0.026 kg·m−3 in ADS-R to approximately 0.004 kg·m−3

in SIEX-R. The reduction was observed in spite of the fact that theqe value for the used AA was greater than for the ion-exchangeresins. This was due to the possibility of performing significantlymore regeneration cycles N in the ion-exchange process, N = 47 inSIEX-R, compared to N = 5 in scenario ADS-R.Regarding the release of pollutants, the four scenarios

produced a solid waste that consisted of the spent adsorbent orresin. The solid wastes were considered hazardous in all thescenarios. The total amount of the As(V) released as liquidwaste is also indicated in Table 1. According to US-EPA, thepH of the resulting regeneration solution should be around12.42 However, the burdens generated by the basic nature ofthe effluent were not considered in this work. In this study, weassumed that the burden associated with the liquid effluentsgenerated in scenarios ADS-R, IEX-R and SIEX-R was due to thepresence of As(V), and it was represented by the metric namedEcotoxity to Aquatic Life (metals). No burdens were derived fromthe release of sulphates, sodium, or chloride because the potencyfactor for seawater was zero for those substances.

Life Cycle Environmental Sustainability Assessment(LCESA). The results of the NRS and EBS for the scenariosADS and ADS-R were compared in order to evaluate the influenceof the regeneration step in terms of primary resources andenvironmental burdens on the adsorption process. Table 2 shows

Table 1. Results of the Scenarios under Study Related to the Functional Unit (G-G step)a

scenarios

final resources (related to the functionalunit) units ADS ADS-R IEX-R SIEX-R

NRS energy electricity kW·h·m−3 0.124 0.124 0.124 0.124adsorbent/resin kg adsorbent or resin·m−3 0.119 0.026 0.004 0.004

materials NaOH kg NaOH·m−3 − 0.292 0.011 0.003NaCl kg NaCl·m−3 − − 0.016 −H2SO4 kg H2SO4·m

−3 − 0.268 − −water water m3·m−3 − 0.008 0.002 0.003

emissions, effluent and wastes (related to thefunctional unit) units ADS ADS-R IEX-R SIEX-R

EBS wastes (land) spent adsorbent kg adsorbent·m−3 0.119 0.026 0.004 0.004As(V) kg As(V)·m−3 − 9 × 10−5 9 × 10−5 9 × 10−5

effluents (seawater) Na+ kg Na+·m−3 − 0.16 0.002 0.013SO4

2‑ kg SO42‑·m−3 − 0.263 − −

Cl− kg Cl−·m−3 − − 0.010 −aADS: adsorption of AA without regeneration; ADS-R: adsorption of AA with regeneration; IEX-R: ion-exchange using commercial resin andconducting a regeneration step, SIEX-R: ion-exchange using lab resin and conducting a regeneration step; NRS: Natural Resources Sustainability,EBS: Environmental Burdens Sustainability.



the primary resources used in the scenarios during the C-G stepand the final resources consumed during the G-G step.The LCESA demonstrated that the regeneration of AA

affected the amount of primary resources consumed during theC-G step in terms of energy, materials, and water. The scenarioADS-R needed a larger amount of the overall primary materials,0.64 kg·m−3, more than in the scenario AA, 0.22 kg·m−3. Thiswas also observed in the usage of the final material resources inthe G-G step: e.g. almost 5 times higher amount of materials inthe scenario ADS-R. Despite of this increment in overallprimary materials required in scenario ADS-R, it should beconsidered that the amount of AA decreased (around 5 timesless), which may be an important advantage in terms of costand economic analysis. Both scenarios consumed the sameamount of final energy based on the same pressure drop.However, the amount of primary energy in ADS-R was about2.6 times higher because of the much larger need of materials.For example, in the case of ADS-R, 86% of the total primaryenergy came from the production of materials, while theremaining 14% was due to the electricity and water. In bothscenarios the contribution of renewable energy was minor.Regarding the water consumption, around 6 times moreprimary water was used in scenario ADS-R compared to thescenario ADS because of the regeneration procedure. Thus,scenario ADS-R consumed more primary energy, materials, andwater than scenario ADS.Concerning the use of primary resources in the removal of

As(V) by ion-exchange, the same pressure drop led to similarconsumption of final electricity. The small difference in theconsumption of primary energy was due to the differentamounts of materials needed in the procedure for theregeneration. The primary materials in the scenario IEX-Rincreased up to 0.09 kg·m−3, which was higher than in thescenario SIEX-R, 0.05 kg·m−3. Similar amounts of primarywater were used in both scenarios because of the similar BV forwater rinsing, with small contributions from C-G step.

The weight of the adsorption or ion-exchange step in thewater treatment process was also evaluated through theintegration of the scenarios in scenario DW. The results forthe four scenarios showed that the consumption of primaryenergy, materials, and water of the treatment plant can increasebetween 27 and 155%, 7−94%, and 0.48−5.3%, respectively.The integration of scenario ADS-R reported the greatest impactwhile the incorporation of the ion-exchange reported a slightincrease. From the NRS perspective, the scenarios IEX-R andSIEX-R were the most adequate alternative.Table 3 indicates the EBS generated in the selected scenarios.

The main burden created by the removal of As(V) byadsorption or ion-exchange processes was allocated in theland compartment in the G-G step. In the scenarios ADS, ADS-R, IEX-R, and SIEX-R, the total dimensionless normalizedindex to land contributed to the total index 99.8, 94.3, 57.1, and57.4%, respectively. It was checked that the use of a morespecific Spanish grid mix47 for the electricity has a very lowinfluence in the total EBS values of the overall processes.These results indicated that the main environmental problem

caused by the adsorption or ion-exchange processes was thegeneration of the hazardous solid wastes.The resulted EBS also showed that the regeneration of the

AA affected the burdens caused by the adsorption process. Thescenario ADS had a total index of 84 compared to the totalindex of 20 corresponding to the scenario ADS-R. These valueswere mainly due to the contribution of the generation ofhazardous solid waste in the G-G step. The higher value ofscenario ADS was due to the G-G burdens derived from themore significant generation of solid hazardous wastes per unitof volume treated. As observed in Table 3, the use of water,NaOH, and H2SO4 in the regeneration procedure resulted inthe increase of the environmental contribution to air and watercompartment 4 and 44 times higher, respectively. On the otherhand, the burden to land in the scenario ADS-R decreased 78%.The comparison among both scenarios showed clearly thetrade-off between usage of chemicals, which contributed to ahigher value of the total index to air and the total index to waterand the generation of spent adsorbents, which contributed to ahigher value of the total index to land. Table 3 also shows thatno release of As(V) to the water compartment took place in thescenario ADS, and a minor As(V) contribution occurred in thescenario ADS-R. Further, the total index to air in the scenarioADS-R was higher than in the scenario ADS: 0.58 vs 0.14, andboth were exclusively due to the C-G step as no emissions to airwere given by the adsorption process itself in the G-G step. Theemissions were given by the POF metric as a consequence ofthe emissions of SF6 during the life cycle production of H2SO4.Finally, the majority of the burdens caused by the scenario ADSand ADS-R to the water compartment occurred during the C-Gstep and G-G, respectively. The burdens produced by thescenario ADS-R to the water compartment were due to therelease of As(V) to seawater. Therefore, scenario ADS-Rprovided the lowest EBS value thanks to the lower productionof hazardous waste.Regarding the two scenarios related to the ion-exchange

process, similar total indexes, around 4, were presented. Thesimilarity in the total indexes for the two resins was based onthe inventories. This total index was much lower than the valueobtained for the two AA related scenarios and the contributionsof total index to air and total index to water to the total indexwere around 31% and 11−12%, respectively.

Table 2. Natural Resource Sustainability Values Obtained forthe Scenarios under Study Related to the Functional Unita

scenarios

primary resources units ADS ADS-R IEX-R SIEX-R DW

primary energy MJ·m−3 3.69 9.75 1.95 1.69 6.28non-renewable 3.60 9.39 1.87 1.62 6.04renewable 0.09 0.36 0.08 0.07 0.24primary materials kg·m−3 0.22 0.64 0.09 0.05 0.69energy resources 0.09 0.27 0.05 0.04 0.18nonrenewableelements

0.07 0.03 0.00 0.00 0.01

nonrenewableresources

0.05 0.33 0.04 0.01 0.46

renewableresources

0.01 0.02 0.01 <0.01 0.03

primary water m3·m−3 0.01 0.06 0.01 0.01 1.14final

resources units AA ADS-R IEX-R SIEX-R DW

energy MJ·m−3 0.44 0.44 0.44 0.44 1.40materials kg·m−3 0.12 0.59 0.03 0.01 0.01water m3·m−3 − 0.01 <0.01 0.01 0.02

aAA: activated alumina; ADS: adsorption of AA without regeneration;ADS-R: adsorption of AA with regeneration; DW: pretreatment ofwater prior to the As removal; IEX-R: ion-exchange using commercialresin and conducting a regeneration step, SIEX-R: ion-exchange usinglab resin and conducting a regeneration step.



Table

3.Dim

ension

less

WeightedEBSMetrics

fortheScenariosun

derStud

ya

Cradleto

Gate(raw

materialsacquisition)

Gateto

Gate(operatio

n)

AA

ADS-R

IEX-R

SIEX

-RDW

AA

ADS-R

IEX-R

SIEX

-RDW

totalindexto

air

1.40

×10

−2

5.80

×10

−1

1.35

×10

01.36

×10

01.86

×10

−1

−−

−−

−AtA

7.77

×10

−3

4.70

×10

24.63

×10

−3

4.25

×10

−3

8.56

×10

−3

−−

−−

−GW

3.27

×10

−3

7.00

×10

−3

1.43

×10

−3

1.25

×10

−3

4.66

×10

−3

−−

−−

−HHE

2.03

×10

−2

8.78

×10

−2

1.48

×10

−2

1.16

×10

−2

3.01

×10

−2

−−

−−

−PO

F8.50

×10

−2

4.03

×10

−1

4.83

×10

−2

4.37

×10

−2

1.26

×10

−1

−−

−−

−SO

D2.40

×10

−2

3.51

×10

−2

1.28

×10

01.30

×10

01.66

×10

−2

−−

−−

−totalindexto

water

1.16

×10

−2

1.05

×10

−2

1.65

×10

−3

1.38

×10

−3

3.26

×10

−3

−4.97

×10

−1

4.97

×10

−1

4.97

×10

−1

−AqA

4.06

×10

−7

3.40

×10

−6

3.04

×10

−7

1.60

×10

−7

7.70

×10

−7

−−

−−

−AOD

1.36

×10

−5

1.48

×10

−5

2.34

×10

−4

2.37

×10

−4

6.08

×10

−6

−−

−−

−MEco

1.56

×10

−3

2.90

×10

−3

4.44

×10

−4

3.62

×10

−4

9.97

×10

−4

−4.97

×10

−1

4.97

×10

−1

4.97

×10

−1

−NMEco

9.20

×10

−4

2.07

×10

−3

2.13

×10

−4

1.47

×10

−4

3.69

×10

−4

−−

−−

−EU

9.07

×10

−3

5.51

×10

−3

7.57

×10

−4

6.38

×10

−4

1.89

×10

−3

−−

−−

−totalindexto

land

−−

−−

−8.21

×10

11.82

×10

12.47

×10

02.51

×10

02.88

×10

−3

HW

−−

−−

−8.21

×10

11.82

×10

12.47

×10

02.51

×10

0−

NHW

−−

−−

−−

−−

−2.88

×10

−3

TOTAL

11

22

183

193

41

aAA:activated

alum

ina,Atm

osphericAcidificatio

n(AtA),GlobalW

arming(G

W),Hum

anHealth

(Carcinogenic)

Effects(H

HE),P

hotochem

icalOzone

(Smog)Fo

rmation(POF),StratosphericOzone

Depletio

n(SOD),AquaticAcidificatio

n(AqA

),AquaticOxygenDem

and(AOD),Ecotoxicity

toAquaticLife

(metalsto

seaw

ater)(M

Eco),Ecotoxicity

toAquaticLife

(other

substances)(N

MEco),

Eutrophicatio

n(EU),Hazardous

Wastes(H

W)andNon-H

azardous

Waste

(NHW).ADS:

adsorptio

nof

AAwith

outregeneratio

n;ADS-R:adsorptio

nof

AAwith

regeneratio

n;IEX-R:ion-exchange

usingcommercialresinandconductin

garegeneratio

nstep,S

IEX-R:ion-exchange

usinglabresinandconductin

garegeneratio

nstep.



From a process engineering perspective, it is stronglyrecommended to reduce the generated solid waste in orderto decrease the total index. For example, in the scenario ADS-R,the total index to land represented 94% of the total burden.Under proper management, the solid waste would beconsidered as nonhazardous, and the burden to the landcompartment would be 3 orders of magnitude lower. In thatcase, the weighting factor is 2,000,000 tons of nonhazardouswastes instead of 2,000 tons of hazardous waste,46 and the totalindex to land would be 0.08; the main concern would be the aircompartment. As expected, the release of As in the G-G stepwould be the mayor contributor to the burdens to water, i.e.,45% of the total index. Assuming that the spent adsorbentwould be nonhazardous, the total index would be 2.Further, the total index for the scenario DW was 0.19 and

consequently this value was negligible compared to the totalindex of each scenario based on adsorption or ion-exchangeprocesses.

■ CONCLUSIONS

The Environmental Sustainability Assessment of differentAs(V) removal techniques gives insights into the efficiency ofthe resource usage and the environmental burdens due to theprocesses themselves.This work concludes that the regeneration of AA implies a

larger consumption of resources but a decrease of the amountof environmental burdens per unit of m3 of treated water. Theresults indicate that the removal of As(V) by ion-exchangeusing any of the resins under study decrease the resource usageand generated burdens compared to performing the removalusing adsorption. However, potential loss of exchange capacityof the resin will affect the results. Further studies shall take thisissue into account for a proper analysis of each resin process.This study also shows that the total land index of all the

scenarios based on adsorption or ion-exchange had the highestvalue in the environmental burdens because of the hazardouscharacteristics of the spent material used for the removal ofAs(V). This work highlights the importance of the proper wastemanagement strategy, which would avoid the return of theseparated As(V) to water bodies. The removal of As(V) in adrinking water treatment plant would increase notably theNRS: primary energy, materials, and water of the treatmentplant between 27 and 155%, 7−94%, and 0.48−5.3%,respectively. This way, the EBS of the facility would also risefrom a total index of 0.19 to 5−84.Future research is expected to focus on other enhanced

treatment such as membrane technologies and also in the ESAof the additional processes needed to treat the liquid wastesfrom regeneration. The additional research will give crucialinsights regarding the environmental sustainability of thedifferent operations which will aid in future decision makingfrom a holistic perspective.

■ ASSOCIATED CONTENT

*S Supporting InformationThis material is available free of charge via the Internet athttp://pubs.acs.org.

■ AUTHOR INFORMATION

Corresponding Author*E-mail: [email protected]

NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTS

This work was conducted as part of the “The application ofGREEN TECHnologies for sustainable water purification andreuse” which is financed by the Water related research of NewIndigo Programme (FP7). Juan de la Cierva Programme of theSpanish Ministry of Economy and Competitiveness is acknowl-edged for the financial support.

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Arsenic Removal from Natural Waters by Adsorption or Ion Exchange: An Environmental Sustainability Assessment

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