chitosan- and iron–chitosan-coated sand filters: a cost-effective approach for enhanced arsenic...

Chitosan- and Iron−Chitosan-Coated Sand Filters: A Cost-EffectiveApproach for Enhanced Arsenic RemovalAnjali Gupta,†,‡ Mohammed Yunus,‡ and Nalini Sankararamakrishnan*,†

†Center for Environmental Science and Engineering, Indian Institute of Technology Kanpur, Kanpur U.P. 208016, India‡Babasaheb BhimRao Ambedkar University, Lucknow, U.P., India

*S Supporting Information

ABSTRACT: This paper describes the potential of chitosan-coated sand (CCS) and iron−chitosan-coated sand (ICCS) towardthe removal of both As(V) and As(III) from aqueous systems. Various parameters including pH, equilibration time, initial arsenicconcentration, and adsorbent dosage have been optimized for maximum adsorption. The adsorption data fitted well in bothLangmuir and Freundlich adsorption models. The Langmuir monolayer adsorption capacity was found to be 17 and 23 mg/g forCCS and 26 and 56 mg/g for ICCS at pH 7 for As(III) and As(V), respectively. The reaction followed a pseudo-first-ordermodel. Column studies revealed higher breakthrough capacity for As(V) using both CCS and ICCS. Adsorption plots were fittedwith BDST model. The adsorbent was also successfully applied for the removal of total inorganic arsenic down to <10 μg L−1

from real life arsenic-contaminated groundwater samples.

1. INTRODUCTION

Arsenic pollution is found worldwide1 and due to its toxiceffects toward human health and the environment, internationalagencies including WHO and U.S.EPA have established themaximum concentration limit (MCL) to be 10 μg/L. The newMCL was later transposed to India through Bureau of Indianstandards (BIS). Due to the drastic reduction of arsenic MCLfrom 50 to 10 ppb, drinking water facilities are undergoingseveral technical and operational changes. It is well-known thatin the aqueous environment arsenic species exist as arsenate (asH2AsO4

− and HAsO42−) in well-oxidized waters and arsenite

(as H3AsO30 and H2AsO3

−) in reduced environments.2 It isreported in the literature that the reduced form, namely thearsenite, is 25−60 times more toxic than arsenate and moremobile in the environment.3 Human health effects of arsenicpoisoning have been adequately reviewed.4−6 Hence, it isimperative that any removal technique to be adopted should becapable of removing both species of arsenic from the aqueoussystem. Various removal methodologies including coagulation/filtration, reverse osmosis, ultra filtration, ion exchange, andadsorption methods have been used for the removal of arsenic.Among these methods adsorption methods are widely used dueto the low cost, high adsorption capacity, and lesser amount ofwaste generated.Previous studies have demonstrated the use of iron bearing

materials such as geothite,7 Fe3O4,8 ferric oxide nanoparticles,9

iron-doped carbon materials,10−12 synthetic pyrite,13 iron-coated sand,14 iron sulfide-coated sand,15 zerovalent iron,16

and mixed oxide-coated sand17 for the removal of arsenic. Itshould be mentioned that most of the adsorbents (except ironoxide-coated sand and synthetic pyrite) have been tested forthe removal of either As(III) or As(V) removal. It is well-known that these iron-based materials have strong affinity toboth forms of arsenic species and could be easily separated byapplication of external magnetic field. It is also well establishedin the literature that chitosanmarine waste from the seafood

processing industryand iron composite was found to beefficient adsorbent toward arsenic removal.18−20 To decon-taminate a waste stream, use of filters containing permeablereactive barriers is found necessary. Though chitosan and iron−chitosan composites are good adsorbents for arsenic, use ofthese materials alone as filter cartridges would be expensive.Hence immobilizing chitosan/iron−chitosan composite on aninexpensive material would pave the way to a cost-effectivetechnology. Studies have been reported on the use of chitosan-coated sand toward the removal of lead and copper.21 Thus, inan effort to synthesize an inexpensive adsorbent that could beused as an affordable material in rural areas, a novel chitosan/iron−chitosan-coated sand was prepared and evaluated for itsefficiency toward the removal of both arsenite and arsenate atneutral pH under equilibrium and dynamic conditions.

2. MATERIALS AND METHODS2.1. Reagents. All reagents were of AR grade. A stock

solution of As(III) and As(V) was made using milli-Q water.Standard acid and base solutions (10% H2SO4 and 10%NaOH) were used for pH adjustments. Sodium arsenatehydrate, Na2HAsO4·7H2O and sodium arsenite NaAsO2(Merck reagent) were used to prepare stock solution of As(III)and As(V) standards. All standard solutions were preparedfresh daily and suitable dilutions were carried out.

2.2. Preparation of Adsorbents. Chitosan-coated sand(CCS) was prepared by using Gangetic belt sand from nearKanpur district. Initially, the sand was sieved to a geometricmean size of 0.3 mm and washed twice with deionized distilledwater and 1 M HCl to remove the adsorbed metal ions thendried at 90 °C for 20 h to activate the sites. Chitosan was

Received: September 10, 2012Revised: December 19, 2012Accepted: January 11, 2013Published: January 11, 2013

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dissolved in 0.05 M acetic acid to make the final concentrationof 0.5% by weight. Then, activated sand was mixed with thedissolved chitosan solution and stirred overnight. The coatedsand was washed with deionized distilled water and dried atroom temperature for further experiments. Iron−chitosan-coated sand (ICCS) was prepared by coating CCS with 0.5 MFe (NO3)3 for half an hour in nitrogen atmosphere, washedthoroughly with distilled water, air-dried, and used for furtherexperiments. The adsorbents used were all sieved through asieve of less than 0.3 mm average particle size range.2.3. Batch Adsorption Experiments. To study the effect

of initial pH (2−10) on arsenic uptake, experiments wereperformed with initial arsenic concentrations of 1000 μg/L at afixed contact time of 2 h. The effect of contact time was studiedwith an initial arsenic concentration of 500 μg/L and adsorbentdose of 2.5 g/L; pH was kept at 7 and contact time was variedfrom 15 to 240 min. Isotherm studies were conducted withvarying initial As(III) and As(V) concentrations (100−1000μg/L), fixed adsorbent dose of 2.5 g/L, and contact time of 2 hat pH 7. The pH of the solution was adjusted to 7 by adding 1.0M sodium hydroxide or 1.0 M hydrochloric acid solutions. Thebatch experiments were carried out at constant temperature in ashaking water thermostat maintained at 25 °C. Theequilibration (shaking) time was 2 h at an agitation speed of110 rpm. After the isothermal equilibration, the sorbent wasseparated by filtration with Whatman 41 filter paper. Thefiltrate was analyzed for arsenic. The amount of the arsenicadsorbed (mg) per unit mass of chitosan (g), qe, was obtainedby mass balance using eq 1

=−

·qec c

mVi e

(1)

where ci and ce are initial and equilibrium concentrations of themetal ion (mg/L), rescpectively, m is dry mass of chitosan (g),and V is the volume of the solution (L).2.4. Column Adsorption Experiments. Dynamic flow

adsorption experiments were conducted in a glass column ofabout 2.2 cm internal diameter and 50 cm length. Each bed ofsorbent was underlain by 2 cm3 of glasswool and 4 cm3 of 3-mm glass beads. The addition of glass wool and glass beads wasmade to improve the flow distribution. The bed height of thecolumn was maintained at 30 cm3. The column was packedwith the adsorbent and shaken so that the maximum amount ofadsorbent was packed in the column without gaps. The influentsolution was pumped from the reservoir into the column by a

Mclins Pump in an up-flow direction. The up-flow mode ofoperation was chosen to increase the contact time and to avoidany channeling of the influent solution. Concentration of theinfluent solution was maintained at 500 μg/L. A constant flowrate of 2 mL/min was maintained throughout the run. The pHof the solution was adjusted to 7.0 ± 0.2 by adding 0.01 Msodium hydroxide or 0.01 M HCl solutions. The effluentsolution was collected at different time intervals, and theconcentration of the metal ion in the effluent solution wasmonitored. There was no significant change in effluent pH. Thesolutions were diluted appropriately prior to analysis. Allexperiments were carried out in duplicates and the deviationswere within 5%.

2.5. Analytical Measurements. Thermo UV−Visible andInfrared (500−4000 cm−1) spectrophotometers were used forcolorimetric and FTIR measurements. Infrared measurementswere made with KBr pellets. Scanning electron microscopy(SEM) was conducted with a FEI Quanta 200 machine. Totalinorganic arsenic and As(III) analyses were carried out byspectrophotometric silver diethyl dithiocarbamate method(APHA, 1998) and inductive coupled plasma mass spectros-copy ICP-MS (Thermo, X-Series2). The lower limit ofdetection was found to be 4 μg L−1 for APHA method and10 ppt for ICP-MS. Calibration was carried out daily withfreshly prepared arsenic standards, before the sample analysis.

2.6. Studies with Real Life Groundwater Samples.Arsenic-contaminated groundwater samples were obtainedfrom the Shuklaganj area of Kanpur district. Characteristics ofthe groundwater obtained are given in the SupportingInformation (S1). Experiments were conducted in batchmode using both ICS and ICCS. Similarly to study the matrixeffects of the groundwater, experiments were also carried outspiking known amounts of As(III) and As(V).

3. RESULTS AND DISCUSSION

3.1. Characterization of Adsorbent. 3.1.1. SEM Analysis.Samples of ICCS before and after loading were examined on anEDAX, FEI Quanta 200 machine operated at 20−30 kV,utilizing both secondary electron and backscattered electrondetectors. Samples were mounted in high-vacuum wax and thencoated in Au prior to analysis. SEM images of ICCS in Figure1a showed very ordered silica crystals at the surface. UnloadedICCS had a relatively uniform and smooth surface, and smallcracks, micropores, or light roughness could be found on thesand surface. Comparing the images of unloaded ICCS (Figure

Figure 1. SEM images of ICCS (a) unloaded and (b) As(V) loaded.

Industrial & Engineering Chemistry Research Article

dx.doi.org/10.1021/ie302428z | Ind. Eng. Chem. Res. 2013, 52, 2066−20722067

1a) and loaded ICCS (Figure 1b), loaded ICCS had asignificantly rougher surface than virgin ICCS and the coatedsand surfaces were apparently occupied by arsenic species.3.1.2. X-ray Diffraction. Figure 2 shows the X-ray diffraction

spectrum of ICCS. The X-ray diffraction spectrum shows peaks

at 2θ = 24.26, 36.5, 39.5, 40.2, 50.11, and 54.86 which arecharacteristic peaks of Akaganeite (β-FeOOH). Reports haveshown that Akaganeite exhibits higher adsorption capacitycompared to other mineral phases of iron.22 It is well-knownthat chitosan is a biopolymer containing amine and hydroxylunits. Thus, it could be postulated that the hydroxyl ions of thechitosan bond with iron to form iron oxyhydroxide. A similarmechanism have been proposed elsewhere with iron-dopedcellulose.23 Peaks at 2θ values 24.26, 36.5, 39.5, 40.2, 50.11, and54.86, which were common to both the samples, werecharacteristic peaks of α−quartz samples. From XRD spectrumdata particle size of material could be calculated by Debye−Sherrer Formula:

λβ

θ=Cs0.9

cos(2)

where Cs is average particle size, λ wavelength of the incidentX-ray beam (in this case 1.54 Å), β is the full width at half-maximum (fwhm; in radian) of the X-ray diffraction peaks, andθ is half of the angle 2θ corresponding to the peak. Using theabove equation the average particle sizes of activated sand at26.63° and ICCS at 26.61° were found to be 5.75 and 11.42 Å/radian, respectively.3.1.3. FTIR Studies. The FTIR spectra of unloaded ICCS and

loaded ICCS with As(III) and As(V) at pH 7 were acquired byTensor 27 (Bruker, Germany) in the attenuated totalreflectance (ATR) mode using Ge crystal (Figure 3). Thesample chamber was continuously purged with nitrogen duringthe measurement. A total of 100 scans were taken for eachsample. From Figure 3 the following observations were made:

a. After adsorption of As(III) and As(V), broadening of thepeak at 3400 cm−1 corresponding to −OH group isobserved

b. Shifting of carbonyl stretching frequencies from 1750cm−1 to higher frequency 1790 cm−1 after arsenic loading

c. A sharp doublet at 1070 cm−1 (−C−O str) after arsenicadsorption

d. Appearance of doublet at 1380 cm−1 (methyne −CH str)after arsenic loading

e. Broadening of the peak corresponding to the −NHstretching at 1650 cm−1

f. Weak IR bands at 880 cm−1 after arsenic loading couldbe attributed to As−O−Fe stretching vibration

g. Disappearance of weak stretching vibration of Fe−O at607 cm−1 after arsenic adsorption

All the above observation suggests that hydroxyl, amino,−CH, carboxyl, and Fe−O are responsible for the adsorption ofarsenic on ICCS.

3.1.4. Surface Area Measurements. Specific surface area andpore size distributions were measured using a QuantachromeAutosorb Automated Gas Sorption System. Sample preparationinvolved degassing the samples overnight (16 h) at 120 °Cunder vacuum. The samples were subjected to 99-point BETsurface area analysis and full adsorption isotherms werecollected for all samples. In addition, micropore and mesoporevolume distribution as a function of pore size were calculatedon the basis of the Horvath−Kawazoe (HK) and Barret, Joyner,and Halenda (BJH) method, respectively. The surface area wasfound to be 0.3978 and 0.3875 m2/g for CCS and ICCS,respectively. It was found that the average pore size distributionand pore diameter was found to be 31.9172 nm and 2.544 Å forboth the samples.

3.2. Effect of Solution Initial pH. The solution pH is animportant factor for all water and wastewater treatmentprocesses because it affects the speciation of metal in water.It is evident from Figure 4 that adsorption increases withincrease in pH and reaches a maximum, and further increase inpH above 7.5 results in decreased adsorption. Maximumadsorption is found to be at pH 6.0 and 6.5 for both As(V) andAs(III) using CCS and ICCS, respectively. The observeddifference between pH’s could be due to the pH-dependent Asspeciation and/or the surface charge on iron oxides. Due topractical reasons, all further experiments were carried out at pH7 with both CCS and ICCS.It has been reported that pKa of chitosan ranges from 6.0 to

7.7 depending on the degree of deacetylation.24 At near neutralpH, it is reported that about 50% of the total amine groups in

Figure 2. X-ray diffraction spectra of plain and iron−chitosan-coatedsand.

Figure 3. FTIR Spectra of ICCS and arsenic-loaded ICCS.



the chitosan remain protonated and theoretically available forthe sorption of metal ions.25 Hence, anionic arsenate ions(H2AsO4

− or HASO42−) are adsorbed on the chitosan

backbone in CCS by simple ion exchange reaction. In thecase of As(III), it could be postulated the reactive carbongroups present on the surface of the sorbent catalyze chargeand redox transformation upon As(III) adsorption.In the case of ICCS, apart from chitosan, hydrated iron oxide

also plays a major role in the adsorption. Maximum adsorptionof As(V) has been reported in the pH range of 4−8 byhydrated ferric oxide, hydrated iron oxide, and iron oxide-coated materials.26−29 Pure iron oxides typically have zero pointcharges (ZPC) in the pH range 7−9.28 Over these ZPC values,iron oxides are present in the monomeric anionic form[Fe(OH)4]

− hence inappropriate for adsorbing anioniccomponents. Below pH 7 iron oxide exists as cationic monomerFe(OH)2

+. This explains the increased adsorption at pH < 7.Decreased adsorption at higher pH’s could be attributed to therepulsion between anionic ferric hydroxide and arsenic ions.For practical reasons, and because most of the groundwaterexists between pH 7 and 7.5, further experiments wereconducted at pH 7 for both the adsorbents.3.3. Kinetic Study of Adsorption. It was observed that

adsorption of As(III) and As(V) increased with an increase incontact time, and the equilibrium was achieved afterapproximately 2 h for both CCS and ICCS. Such a shortadsorption time was probably due to the efficient reactioncaused by the adsorbent composition of the materials. Theexperimental data were analyzed using a pseudo-first-orderequation (eq 3)

=Kt

CoCe

2.303log

(3)

where Co and Ce are the amount of initial arsenic species takenin the solution and amount of arsenic adsorbed at pseudoequilibrium condition and at time t, respectively, and K is theadsorption rate constant. The rate constants for As(V) andAs(III) using CCS were found to be 1.0948 and 0.38078 h−1,respectively. In the case of ICCS the values obtained for therate constants were 0.7572 and 1.6097 h−1 for As(III) andAs(V), respectively.

3.4. Sorption Equilibrium Study. The isotherm models ofLangmuir and Freundlich were applied to fit the adsorptionequilibrium data of As(III) and As(V) on CCS and ICCS.Linearized forms of Langmuir and Freundlich isotherms arerepresented by

= +qe QbCe Q1 1 1

(4)

= +qen

Ce Kflog1

log log(5)

where Ce and qe are equilibrium concentration and the amountadsorbed at equilibrium expressed in mg L−1, Q (mg g−1)represents the maximum adsorption capacity, and b (mL mg−1)is the Langmuir constant, which represents the affinity betweenthe solute and the adsorbent. The n and Kf are the Freundlichparameters, for values 1 < n < 10, which indicated adsorption isconsidered to be favorable.Equilibrium adsorption isotherm studies were conducted

with aqueous solutions of As(III) and As(V) varying theconcentration from 100 to 1000 μg L−1 at pH 7 with a dose rateof 2.5 g mL−1 of solution for 2 h in CCS and ICCS,respectively.Linearized Langmuir adsorption plots are shown in Figure 5.

The values obtained for the various parameters of Langmuir

and Freundlich isotherm parameters are shown in Table 1. Theadsorption data could be described well by the Langmuir model(R2 > 0.977) and Freundlich model (R2 = 1), which interpretedthe adsorption process fitted to a monolayer adsorption on a

Figure 4. Effect of initial pH on the adsorption of arsenite andarsenate by CCS and ICCS.

Figure 5. Linearized adsorption isotherms of arsenite and arsenate onCCS and ICCS systems.

Table 1. Langmuir and Freundlich Model Constants

Langmuir model Freundlich model

adsorbentsarsenicspecies

Qmax(mg/g)

b(mL/mg) R2 1/n Kf R2

CCS As(III) 17 1.144 0.817 1 2.49 1As(V) 23 1.016 0.946 1 2.49 1

ICCS As(III) 26 1.09 0.986 1 2.50 1As(V) 56 1.04 0.977 1 2.50 1



homogeneous surface. The Freundlich parameters for n valuewere both higher than 2.4, indicated that arsenic was favorableto adsorption on adsorbents. It can be seen from the values ofQmax (mg g−1) in Table 1 that the maximum adsorptioncapacities obtained for ICCS were 26 and 56 mg g−1 and forAs(III) and As(V), respectively, at pH 7, which was muchhigher than that for CCS. Compared with other adsorbents inTable 2, the adsorption capacities of CCS and ICCS are more

than twice as much as that of FeS-coated sand34 and many foldshigher than iron oxide-coated sand35 has been reported. Itshould be noted that the main advantage of the adsorbent is theversatility toward the removal of both As(III) and As(V) atnear neutral pH.3.7. Application of the Adsorbent toward Arsenic

Removal. Results obtained from batch studies for arsenic-contaminated groundwater obtained from the Shuklaganj areaof Kanpur district, UP, is shown in Table 3. With a dose rate of

5 g L−1 arsenic concentration was reduced to <0.5 μg L−1 withCCS, and arsenic was not detected in samples treated withICCS. This demonstrates the applicability of both theadsorbents in groundwater matrices.3.8. Column Studies. Column studies were carried out

with CCS and ICCS to demonstrate the applicability of theadsorbent for the removal of arsenite and arsenate underdynamic conditions. Column experiments were conductedusing As(III)/As(V) spiked water. The concentration of theinfluent was maintained at 500 μg L−1. The breakthroughcurves for arsenite and arsenate with CCS and ICCS are shownin Figure 6. It is evident from the figure that 16.9 and 31.6 bedvolumes of As(V)-spiked water were treated in columnexperiments using ICCS and CCS, respectively, reducing

arsenic concentration from 500 μg L−1 to <10 μg L−1. Theplots indicate that arsenic concentration below 10 μg L−1 wasfound in the effluent up to about 14.7 and 27.4 bed volumes ofAs(III) using ICCS and CCS, respectively. Higher break-through capacity was observed for As(V) using both CCS andICCS. The adsorption bed was considered to be exhaustedwhen concentration of the effluent coming out of the columnexceeded 50 μg L−1.

3.8.2. Effect of Bed Height. Using Bohart−Adams approachat least nine individual column tests must be conducted tocollect the required laboratory data which is a time-consumingtask. A technique has been described by Hutchins36 whichrequires only three column tests to collect the necessary data.In this technique, called the bed depth service time (BDST)approach, the Bohart−Adams equation is expressed as

= +t aZ bb (6)

= =aN

C Vslope 0

0 (7)

= =−⎛

⎝⎜⎞⎠⎟b

KaCC

Cintercept

1ln

1

b0

0

(8)

where tb is the time at which metal concentration in the effluentreached 0.01 μg L−1 (h) and Z is the bed height (cm).Theparameters N0 and Ka can be calculated from the slope of thelinear plot of tb versus Z. Figure 7 shows the BDST plot for

Table 2. Comparison of Adsorption Capacities of SomeAdsorbents toward Arsenic Removal (pH is Shown inParantheses)

capacity obtained fromLangmuir model (mg/g)

adsorbents As III As V refs

goethite 10.1 (7.5) 12.1 (7.5) 30hematite 10.0 (7.3) 31.3 (7.3) 30ferrihydrite 0.58 (4.2) 0.16 (9.2) 31Fe and Mn oxide-coated sand 0.129 (7.2) - 32FeS-coated sand 10.7 (7) - 33iron oxide-coated sand 0.136 (7.6) - 34zerovalent iron-coated sand 70.4 (7.0) - 35chitosan-coated sand 17 (7) 23 (7) present workFe−chitosan-coated sand 26 (7) 56 (7) present work

Table 3. Application of CCS and ICCS toward the Removalof Arsenic from Contaminated Groundwater

total arsenicconcentration (μg/L)

adsorbent−adsorbate systembeforeloading

afterloading

CCS + unspiked groundwater 204.0 0.04ICCS + unspiked groundwater 204.0 N.D.CCS + spiked groundwater (250 μg/L As(III) +250 μg/L As(V))

704.0 0.20

ICCS + spiked groundwater(250 μg/L As(III) +250 μg/L As(V))

704.0 N.D.

Figure 6. Breakthrough curves of arsenite and arsenate using CCS andICCS. Conditions: inlet concentration of As(V)/As(III) 500 μg/L,flow rate 2 mL/min, pH 7.

Figure 7. Bed depth service time plots for arsenite and arsenate atbreakthrough concentration of 10 μg/L.



CCS and ICCS for a volumetric flow rate of 2 mL min−1 (linearflow rate = 38.2 cm h−1). The linear relationship obtained forAs(V) and As(III) sorption on CCS and ICCS from the beddepth plot for a breakthrough concentration of 0.05 μgL−1 at aninitial concentration of 0.5 mg L−1 is given in eqs 9, 10, 11, and12, respectively:

= −t Z3.4 16.66b (9)

= −t Z1.8 1.33b (10)

= −t Z3.5 9.33b (11)

= −t Z2.9 12.66b (12)

The saturation concentrations (N0) and the rate constant (Ka)obtained from BDST for CCS and ICCS are given inSupporting Information (S2). The BDST model parameterscan be useful to further scale up the process for other flow rateswithout further experimental run.3.9. Conclusions. Chitosan-coated sand (CCS) and iron−

chitosan-coated sand (ICCS) were prepared, and theirsuitability for the removal of both As(III) and As(V) byequilibrium and dynamic conditions at near neutral pH wasevaluated. The equilibrium data were fitted to Langmuir andFreundlich adsorption models, and the various modelparameters were evaluated. The monolayer adsorption capacityfrom the Langmuir model for CCS (17.0 mg/g for As(V) and23.0 mg/g for As(III)) were found to be lower than thatobtained for ICCS (26.0 mg/g for As(V); 56.0 mg/g forAs(III)). The bed depth service time model constants wereevaluated and proposed for the use in column design. BothCCS and ICCS were found to be efficient in the removal oftotal inorganic arsenic from contaminated groundwater. Finally,immobilization of chitosan/iron−chitosan on sand could pavethe way to an economical solution for the treatment of arsenic-contaminated waters.

■ ASSOCIATED CONTENT*S Supporting InformationTables S1 and S2 as mentioned in the text. This material isavailable free of charge via the Internet at http://pubs.acs.org.

■ AUTHOR INFORMATIONCorresponding Author*Tel.: +91 512 2596360. E-mail: [email protected] authors declare no competing financial interest.

■ ACKNOWLEDGMENTSN.S. is thankful to Council of Scientific and Industrial Research(Scheme 24(306)09-EMR-II) for financial support to carry outthis work. A.G. is thankful to CSIR for Senior Researchfellowship.

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chitosan- and iron–chitosan-coated sand filters: a cost-effective approach for enhanced arsenic...

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