Bioresource Technology 101 (2010) 2173–2179

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Bioresource Technology

journal homepage: www.elsevier .com/locate /bior tech

Column studies on the evaluation of novel spacer granules for the removal ofarsenite and arsenate from contaminated water

Anjali Gupta, Nalini Sankararamakrishnan *

Center for Environmental Science and Engineering, Indian Institute of Technology, Kanpur, UP 208 016, India

a r t i c l e i n f o a b s t r a c t

Article history:Received 29 June 2009Received in revised form 20 October 2009Accepted 9 November 2009Available online 11 December 2009

Keywords:ArsenicDecontaminationDrinking waterIron dopingChitosan

0960-8524/$ - see front matter � 2009 Elsevier Ltd. Adoi:10.1016/j.biortech.2009.11.027

* Corresponding author. Tel.: +91 512 2596351; faxE-mail address: nalini@iitk.ac.in (N. Sankararamak

Decontamination of arsenic ions from aqueous media has been investigated using iron chitosan spacergranules (ICS) as an adsorbent. Drying of beads saturated with a spacer sucrose was considered as simpletreatment, to prevent the restriction of polymer network and enhance sorption capacity. The novel sor-bent was studied in up flow column experiments conducted at different flow rates, pH and bed depth toquantify the treatment performance. It was found that silicate was more inhibitory than phosphate, andthe silicate in groundwater controlled the arsenic removal efficiency. The column regeneration studieswere carried out for two sorption–desorption cycles using 0.1 N NaOH as the eluant. TCLP leaching testswere conducted on the arsenic loaded adsorbent which revealed the containment of arsenic-laden sludgecan be managed without adverse environmental impact. The developed procedure was successfullyapplied for the removal of both As(III) and As(V) from arsenic contaminated drinking water samples.

� 2009 Elsevier Ltd. All rights reserved.

1. Introduction

In India, arsenic contamination of groundwater used for drink-ing is well documented (Bhattacharya et al., 1997; Nickson et al.,2007). WHO provisional guideline value as well as Bureau of IndianStandard (BIS, 2003) for arsenic in drinking water is 10 lg L�1

(WHO, 2004). Considering the relative risks to life and health thereis a growing interest in using low-cost methods and materials toremove arsenic from drinking water before it may cause significantcontamination. The methods available for the removal of arsenichave been adequately reviewed (Mohan and Pittman, 2007).Though many types of adsorbents have been used, biosorptionseems to be an attractive alternative to existing methods owingto the environment friendly characteristics like biodegradabilityand biocompatibility. Many types of biosorbents including agricul-tural wastes (Amin et al., 2006; Sud et al., 2008; Ranjan et al.,2009), sulfate reducing bacteria (Teclu et al., 2008), fungus (Kavithaet al., 2008), and biopolymers (Tiwari et al., 2008; Guo et al., 2007)have been reported. Among the biopolymers, chitosan have beenproven to be an efficient heavy metal scavenger due to thepresence of hydroxyl and amino group (Guibal, 2004). Recentlyremoval of both As(III) and As(V) by chitosan coated alumina hasbeen reported (Boddu et al., 2008). Though this method reports avery high adsorption capacity at pH 4 (56.50 and 96.46 mg g�1

for As(III) and As(V), respectively), the efficiency of this adsorbentwith various interfering ions and its applicability to arsenic con-

ll rights reserved.

: +91 512 2597759.rishnan).

taminated ground water need to be addressed. Chitosan impreg-nated with molybdate has been used to remove As(III) and As(V)from water samples (Chen et al., 2008). Though the resin is effec-tive in the removal of both the species, at pH 5, phosphate is a seri-ous interferent and removal of arsenic is not accomplished in thepresence of phosphate.

Recently, we had evaluated iron coated chitosan flakes andbeads for the removal of arsenic from ground water (Gupta et al.,2009). The capacity of flakes (22.47 ± 0.56 mg g�1 for As(V) and16.15 ± 0.32 mg g�1 for As(III)) was found to be considerably high-er than those of beads (2.24 ± 0.04 mg g�1 for As(V);2.32 ± 0.05 mg g�1 for As(III)). The lower capacity of the beadscould be attributed to the destruction of polymer network duringdrying process. Hence, in this study to retain the polymer network,a spacer namely sucrose was used during drying process (Ruizet al., 2002). Due to affinity of Fe(III) towards arsenic, chitosanwas initially doped with Fe(III) and casted as gel beads. The castedbeads were cross-linked with gluteraldehyde to increase the stabil-ity and dried after saturation with a spacer, sucrose (ICS). The pres-ent work is aimed at the applicability of ICS towards the removal ofboth As(III) and As(V) from ground water matrix using fixed bedcolumn reactor. The evaluations were carried out systematically,and effect of various column parameters including pH, bed depthand flow rate were studied. It is well known from literature thatboth silicate and phosphate has high sorption affinity towards ironhydroxide surfaces (Davis et al., 2002; Kang et al., 2003; Iesan et al.,2008; Zeng et al., 2008). Therefore, the performance of developedadsorbent towards arsenic removal was evaluated in the presenceand in the absence of competing ions including silicate and

2174 A. Gupta, N. Sankararamakrishnan / Bioresource Technology 101 (2010) 2173–2179

phosphate. The recyclability of the adsorbent was studied and ap-plied for the removal of total inorganic arsenic from arsenic con-taminated ground water obtained from Kanpur district, UP. TCLPleaching tests were conducted on the arsenic loaded adsorbentwhich revealed the containment of arsenic-laden sludge can bemanaged without adverse environmental impact even in a ruralenvironment.

2. Methods

2.1. Reagents

Chitosan flakes was acquired from India Sea foods, Cochin, Indiaand used without any further purification. The degree of deacety-lation was reported to be 88% by the manufacturer. Arsenate andarsenite stock solutions were prepared from sodium arsenate (Na2-

HAsO4�7H2O, Merck) and arsenic oxide (As2O3, Sigma Aldrich),respectively. Sodium borohydride (NaBH4, Sigma Aldrich) has beenused for the analytical determination of arsenic. All other chemi-cals used were of analytical grade.

2.2. Analysis

Perkin Elmer UV–Visible and Infra-red (500–4000 cm�1) spec-trophotometer were used for colorimetric and FTIR measurements.Infra-red measurements were made with KBr pelts. Scanning Elec-tron Microscopy (SEM) was done on EDAX, FEI Quanta 200machine.

Total inorganic arsenic and As(III) analysis were carried out byspectrophotometric silver diethyl dithiocarbamate method (APHA,1998). The lower limit of detection was found to be 4 lg. Eachsample was analyzed twice. The co-efficient of variation in theduplicate samples was 2.5%. The average total arsenic level in 20aqueous calibration check samples spiked with 50 lg As was52 ± 4.0 lg. Calibration was carried out daily with freshly preparedarsenic standards, before the sample analysis.

2.3. Preparation of iron doped spacer chitosan granules

Initially iron doped chitosan granules were prepared by placingplain chitosan flakes (3 g) in 100 mL 5% acetic acid (v/v). The mix-ture was stirred in a magnetic stirrer for 4 h. Then to this viscoussolution added of ferric chloride (1 g) and placed in the shakerfor overnight. Now, this viscous solution was dropped into an alka-line sodium hydroxide solution (3 M) through dropper (2 mm,internal diameter) and the beads were collected after 30 min fromthe NaOH bath and then thoroughly washed with distilled wateruntil the there was no further change in pH (�7). Chitosan beads(5 g) obtained by the above procedure were cross-linked with0.05 mL of gluteraldehyde (25%) in 100 mL methanol. After stirringfor 2 h the product was filtered and washed with water and placedin 100 mL of saturated solution for 16 h. Then, it was filtered airdried and then washed with distilled water to remove the sucrosemolecules and finally the gel beads were air dried for 2 days to ob-tain dry ICS. Approximate size of the bead obtained was in therange of 0.8–1.0 mm.

Table 1Characteristics of drinking water.

Sample As(III) As(V) ORP pH Nitr

IIT K drinking water 0 0 �72.0 7.33 1.3Sample from Shuklaganj, Kanpur district 22 157 �115.4 7.09 1.0

As(III), As(V) in lg/l, ORP in mV, nitrate, sulfate, iron ammonia, hardness, TOC, silicate a

2.4. Batch adsorption experiments

Batch equilibrium adsorption isotherm studies were conductedwith aqueous solutions of As(III) and As(V) varying the concentra-tion from 1 to 10 mg in 125 mL Erlenmeyer flasks. Amount ofadsorbent used was 0.1 g and the solution volume was maintainedat 20 mL. The pH of the solution was adjusted to seven by adding1.0 M sodium hydroxide or 1.0 M nitric acid solutions. The pHwas measured using a Wagtech hand held pH meter (WagtechInstruments, UK). The batch experiments were carried out at con-stant temperature in a shaking water thermostat maintained at25 �C. The equilibration (shaking) time was 4 h at an agitationspeed of 200 rpm. After the isothermal equilibration, the biosor-bent was separated by filtration with Whatman 41 filter paper.The filtrate was analyzed for arsenic. The amount of the arsenic ad-sorbed (mg) per unit mass of chitosan (g), qe, was obtained bymass balance using the Eq. (1)

qe ¼ Ci� Cem

� V ð1Þ

where Ci and Ce are initial and equilibrium concentrations of themetal ion (mg/L), m is dry mass of chitosan (g) and V is the volumeof the solution (L).

2.5. Sorption–desorption in fixed bed column reactor

Sorption in a continuous-flow system was done in a fixed bedcolumn reactor (2.2 cm i.d., 30 cm column length). Each bed of sor-bent of desired height was underlain by 4 cm3 of glass wool and6 cm3 of 3 mm glass beads. The addition of glass wool and glassbeads was made to improve the flow distribution. The feed waterused was our institute drinking water (composition of the feedwater is given in Table 1) spiked with arsenic having an initial con-centration of 0.5 mg. The pH was adjusted to seven and pumpedthrough column at a desired flow rate by a peristaltic pump (Mic-lins) in an upflow mode. Samples were collected from the exit ofthe column at different time intervals and analyzed for arsenic.Operation of the column was stopped when the effluent metal con-centration exceeded a value of 0.05 mg L�1. The column bed wasthen rinsed by passing 100 mL deionised water in upward direc-tion at the same speed as used for sorption from the arsenic metalsolution. The effects of silicate and phosphate were studied by pre-paring the arsenic spiked deionised water with and without theseions at pH 7. The removal efficiency of both As(III) and As(V) werestudied in the presence and absence of these interfering ions.Desorption was carried out by passing 0.1 N NaOH through the col-umn bed in upward direction at a flow rate of 10 mL min�1. Theeffluent metal solution was collected and analyzed for arsenic con-tent. On the completion of desorption cycle, the column was rinsedwith deionised water in the same manner as for sorption till theeluting deionised water attained pH 7.0. The desorbed and regen-erated column bed was reused for next cycle. All experiments werecarried out in duplicates and the deviations were within 5%. For allgraphical representations, the mean values were used. All statisti-cal analyses were made using ORIGIN PRO 6.1 software.

ate Sulfate Iron Ammonia Hardness TOC Silicate Phosphate

28 1.12 0.25 160 10.26 5.3 0.10035 3.5 2.12 500 14.27 7.7 1.428

nd phosphate in mg/l.

0 20 40 60 80 100 1200

10

20

30

40

50

60

Con

cent

ratio

n of

the

efflu

ent (

ug/l)

Bed Volumes

As(III) pH 6 As(III) pH 7 As(III) pH 8 As(V) pH 6 As(V) pH 7 AS(V) pH 8

Fig. 1. Effect of initial pH. Conditions: Influent arsenic concentration 500 lgl�1; Beddepth 20 cm; Flow rate 2 mL min�1.

A. Gupta, N. Sankararamakrishnan / Bioresource Technology 101 (2010) 2173–2179 2175

2.6. Drinking water samples

Drinking water samples were procured from our institute (IITKanpur) which was devoid of arsenic and arsenic contaminateddrinking water samples were acquired from India Mark II handpumps (depth 30–33 m) in Shuklaganj area of Kanpur district,UP, India during January 2009. The characteristics of the waterare given in Table 1.

2.7. Modeling and analysis of column data

A number of mathematical models have been developed for theuse in design of column parameters. Among various models, modelproposed by Bohart and Adams is widely used (Sankararamakrish-nan et al., 2008). The simplified equation of Bohart and Adamsmodel is as follows:

t ¼ N0ZC0m� 1

KaC0ln

C0

Cb� 1

� �ð2Þ

where C0 is the initial metal ion concentration (mg L�1); Cb is thebreakthrough metal ion concentration (mg L�1); N0 is the sorptioncapacity of bed (mg L�1); m is the linear velocity (cm h�1) and Ka

is the rate constant (L mg�1 h�1).Eq. (2) can be used to determine the service time (t), of a column

of bed height Z, given the values of N0, C0 and Ka which must bedetermined for laboratory columns operated over a range of veloc-ity values, m.

3. Results and discussion

3.1. Characteristics of the adsorbent

The surface morphology of ICS characterized by ESEM indicatesa microporous and fibrous structure. The shapes of the beads werenot completely spherical and the size of beads ranged from 0.60 to0.70 mm. The surface was rough and folded due to the drying theprocedure. The EDAX plot of ICS indicated the iron content to be13.23%. The surface area by BET method was found to be1.48 m2 g�1 and pore volume of 7.647 � 10�4 cc g�1.

3.2. Effect of initial pH of the feed water on the adsorption behavior

Variation of intital pH of the feed water was carried out at 6, 7and 8 using 500 lg of As(III) or As(V) spiked ground water. The bedheight was maintained at 20 cm. The results obtained are shown inFig. 1. It is evident that maximum adsorption of arsenic is observedfor As(III) and As(V) at pH 7. Batch experiment were also carriedout with varying pH from 4 to 10. It was found that maximumadsorption was obtained at pH 7 for both As(III) and As(V) in batchstudies as well (Supporting information T1). The adsorption maxi-mum at pH 7 is typical for As(V) but not for As(III). It has been re-ported that close to 100% As(V) adsorption was observed in the pHrange of 4–8 by hydrated ferric oxide (Hsia et al., 1994). A similarobservation is reported by many researchers for arsenate removalby either hydrated iron oxide or iron coated materials (Edwards,1994, Katsoyiannis and Zouboulis, 2002; Mu~noz et al., 2002; Guanet al., 2008). However, in the case of arsenite, it is possible that thereactive carbon groups present on the surface of the sorbent cata-lyze charge and redox transformation upon As(III) adsorption.FeOH�4 exists in high pH values, and FeOHþ2 in acidic solutions. Ironoxide surfaces are comprised of Fe(O,OH)6 octahedra, in whicharsenite or arsenate tetrahedra could be attached in differentmodes (Waychunas et al., 1993). To evaluate the fate of adsorbedarsenite species, speciation studies were conducted after desorp-tion of adsorbed As(III) by 0.1 N NaOH. Analysis of the desorbed

solution revealed that 30% of As(III) adsorbed has been oxidizedto As(V) over the surface of the adsorbent. XPS studies on As(III)loaded iron doped chitosan revealed the presence of both As(III)and As(V) on the surface (Gupta et al., 2009).

It is also well known that the pKa of chitosan ranges from 6.3 to7.7 depending on the degree of deacetylation (Guibal, 2004). Atneutral pH, it is reported that about 50% of the total amine groupsin the chitosan remain protonated and theoretically available forthe sorption of metal ions (Elson et al., 1980). Hence, anionic arse-nate ions are adsorbed on the chitosan backbone by simple ion ex-change reaction. Elson et al. (1980) also reported that there existschelation of arsenate and chitosan apart from electrostatic, ion ex-change. Hence, from the above discussions it could be concludedthat both chitosan and iron play an important role in adsorptionof arsenic from aqueous solutions.

3.3. Sorption equilibrium

The amount of arsenic adsorbed per unit mass of the sorbent, qe(mg g�1) were correlated with the liquid phase concentration atequilibrium Ce (mg) using Langmuir isotherm models. The Lang-muir isotherm is represented by

qe ¼ qmaxbCe=ð1þ bCeÞ ð3Þ

where qe is the equilibrium adsorbate loading on the adsorbent, Cethe equilibrium concentration of the adsorbate, qmax the ultimatecapacity, b the relative energy (intensity) of adsorption, also knownas binding constant.

Langmuir monolayer adsorption capacity was found to be22.57 ± 1.2 mg g�1 and 25.84 ± 1.3 mg g�1at pH 7 for As(V) andAs(III), respectively. Our own earlier studies on iron doped chitosangranules without spacer revealed the monolayer adsorption capac-ity to be 2.32 and 2.24 mg g�1 for As(III) and As(V), respectively(Gupta et al., 2009). Increased uptake capacity up to 10-fold couldbe attributed to the use of spacer during drying processes whichresulted in increased porosity. Earlier studies on plain chitosanrevealed no uptake for As(III) and 58.0 mg g�1 for As(V) at pH 4(Mcafee et al., 2001). When the adsorbent was applied to removalof arsenate from simulated gold mine effluent the capacity wasfound to decrease to 6.0 mg g�1. The main advantage of the sorbent

2176 A. Gupta, N. Sankararamakrishnan / Bioresource Technology 101 (2010) 2173–2179

used in the present study is the applicability for the removal ofboth the species of arsenic at neutral pH and it is well known thatboth As (III) and As (V) coexist in ground water in various parts ofthe world (Chauhan et al., 2009).

0 50 100 150 200 250 300 3500

10

20

30

40

50

60

Con

cent

ratio

n of

the

efflu

ent (

ug/l)

Bed Volumes

As(V) 2 ml/min As(V) 3.5 ml/min As(V) 5 ml/min As(III) 2 ml/min As(III) 3.5 ml/min As(III) 5 ml/min

Fig. 2. Effect of flow rate. Conditions: Influent arsenic concentration 500 lg L�1;Bed depth 20 cm; pH 7.

0 100 200 300 4000

10

20

30

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50

60

Con

cent

ratio

n of

the

Efflu

ent (

ug/l)

Bed Volumes

10 cm As(V) 20 cm As(V) 30 cm As(V) 10 cm As(III) 20 cm As(III) 30 cm As(III) 10 cm As(V)+As(III) 20 cm As(V)+As(III) 30 cm As(V)+As(III)

Fig. 3. Effect of bed depth. Conditions: Influent arsenic concentration 500 lg L�1,pH 7, flow rate 2 mL min�1.

Table 2BDST plot for arsenic using ICS.

Influent Breakthrough concentration at 10 lg L�1

Slope(h cm�1)

Intercept(h)

R2 N0

(mg l�1)k(lmg

As(III) (500 lg L�1) 8.8 73.33 0.97 554.4 0.10As(V) (500 lg L�1) 10.25 85 0.99 645.7 0.09As(III) (250 lg L�1) + As(V)

(250 lg L�1)8.55 84.3 0.97 538.6 0.09

EBCT = 14.25 min; Flow rate 120 cm h�1.

3.4. Effect of flow rate on arsenic adsorption

Experiments were conducted in the continuous-flow fixed col-umn with the IIT Kanpur groundwater spiked with 500 lg L�1.The bed height was maintained at 20 cm and the flow rates werechanged from 2 to 5 mL min�1 while pH of the inlet feed was heldconstant at pH 7.0. Variation of flow rates were conducted for bothAs(III) and As(V) solutions. The plots of comparative normalized ar-senic concentration versus effluent volume at different flow ratesare given in Fig. 2. As indicated in Fig. 3, at the lowest flow rateof 2 mL min�1, relatively higher uptake values were observed forboth arsenite and arsenate sorption to ICS. In general, for both ar-senic species, sharper breakthrough curves were obtained at higherflow rates. The breakpoint time and total adsorbed arsenic quantityalso decreased with increasing flow rate. This behavior can be ex-plained by the fact that arsenic sorption is affected by insufficientresidence time of the solute in the column. This insufficient timedecreases the bonding capacity of the arsenic ions onto FeOOHgroup present in the sorbent. Considering 50 lg L�1 as the breakthrough point, with 2 mL min�1 flow rate and at an initial arsenicconcentration of 500 lg L�1, 250 and 207 bed volumes of As(III)and As(V) solutions were treated, respectively. Using theMCL = 10 lg L�1 as the breakthrough point, 132 and 210 bed vol-umes of As(III) and As(V) solutions were treated, respectively,bringing down the concentration from 500 to 10 lg L�1.

3.5. Effect of bed depth

The breakthrough curves obtained for a bed height of 10, 20 and30 cm at pH 7 using arsenic spiked ground water at a flow rate of2 mL min�1 are shown in Fig. 3. Initial concentration of As(III),As(V) or As(III) + As(V) was maintained at 500 lg L�1. Using Bo-hart–Adams approach at least nine individual column tests mustbe conducted to collect the required laboratory data which is atime consuming task. A technique has been described by Hutchin(1973) which requires only three column tests to collect the neces-sary data. In this technique, called the Bed depth service time(BDST) approach the Bohart–Adams equation is expressed as

tb ¼ aZ þ b ð4Þ

where

a ¼ slope ¼ N0

C0vð5Þ

b ¼ intercept ¼ 1kaC0

lnC0

Cb� 1

� �ð6Þ

tb, the time at which metal concentration in the effluent reached0.01 or 0.05 mg L�1 and Z is the bed height (cm). The parametersN0 and ka can be calculated from the slope of the linear plot of tb

versus Z. Table 2 shows the results of BDST plot for As(III), As(V)and mixture of As(III) and As(V) for a volumetric flow rate of2 mL min�1 (linear flow rate = 126.0 cm h�1). The linear relation-

Breakthrough concentration at 50 lg L�1

h�1)Zc(cm)

Slope(h cm�1)

Intercept(h)

R2 N0

(mg l�1)k(lmgh�1)

Zc(cm)

61 8.33 15.45 94 0.99 973.3 0.0467 6.115 7.98 16.5 117.6 0.99 1039.5 0.0373 7.022 9.87 9.0 20.67 0.99 567.0 0.2126 2.3

0 100 200 300 400 5000

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50

10

20

30

40

50

60

nc. o

f ars

enic

in th

e ef

fluen

t (ug

/l) As(V)

As(III)

(b)

(a)

Con

c. o

f ars

enic

in th

e ef

fluen

t (ug

/l)

Bed Volumes

A. Gupta, N. Sankararamakrishnan / Bioresource Technology 101 (2010) 2173–2179 2177

ship obtained for As(III), As(V) and As(III) + As(V) sorption on ICSfrom the bed depth plot for a breakthrough concentration of0.01 mg L�1 at an initial concentration of 0.05 mg L�1 is given inEqs. (7)–(9), respectively:

tb ¼ 102:5 Z � 85 ð7Þtb ¼ 88 Z � 73:33 ð8Þtb ¼ 85:5 Z � 84:33Þ ð9Þ

The saturation concentrations (N0) and the rate constant (ka)obtained from BDST plots are given in Table 2. The critical beddepth (Z) required for preventing arsenic concentration exceedabove 0.01 or 0.05 mg L�1, which is obtained by substituting t = 0in expression (2), is given below:

Z ¼ V0

KaN0ln

C0

Cb� 1

� �ð10Þ

The critical depth values obtained for As(III), As(V) and mixtureof As(III) and As(V) at 0.01 mg L�1 breakthrough 0.83, 0,83 and0.99 cm, respectively.

BDST model can be used to design systems for treating otherinfluent solute concentrations. When an experiment conductedwith C1, yields an equation of the form

tb ¼ a1Z þ b1 ð11Þ

the predicted equation for the new influent solute concentration C2

is given by

tb ¼ a2Z þ b2 ð12Þ

The new slope and intercept values can be determined asfollows

a2 ¼ a1C1

C2ð13Þ

b2 ¼ b1C1

C2

ln½C2=Cb� � 1ln½C1=Cb� � 1

� �ð14Þ

where a1 and a2 are slopes, s1 and s2 are intercepts at influent con-centration C1 and C2, respectively. Cb is the break through concen-tration for C1 and C2. The degree of predictability for a differentinitial concentration of arsenic by BDST model was evaluated byrunning two columns of 1 mg/l of As(III) and As(V) at flow rate of2 ml/min and column bed depth of 20 cm. The results obtainedare furnished in Table 3 from which it is evident that the system fol-lows BDST approach. The BDST model parameters can be useful tofurther scale up the process for other flow rates without furtherexperimental run.

3.6. Interference effect of phosphate and silicate ions on uptake ofAs(III) and As(V)

The interfering effect of common anions including phosphateand silicate were examined using ICS in fixed bed column andthe results obtained are shown in Fig. 5. Oxy acids namely, phos-

Table 3Comparison of theoretical and experimental breakthrough time using BDST model.

Influent Breakthrough time at10 lg L�1 (h)

Breakthrough time at50 lg L�1 (h)

Theoretical Experimental Theoretical Experimental

As(V) (1.0 mg l�1) 60.2 59.0 106.0 104.5As(III) (1.0 mg l�1) 51.5 50.5 107.7 105.0

EBCT = 14.25 min; Flow rate 126 cm h�1; Bed depth 20 cm.

phate and silicate affected the adsorption of arsenic in both As(III)and As(V) systems. It is well known that phosphate strongly sorbsonto iron oxides similar to arsenate (Manning and Goldberg, 1996;Jain and Loeppert, 2000; Gao and Mucci, 2001; Dixit and Hering,2003) and can therefore compete with arsenic for binding sites.It is reported at lower pH phosphate has an increasing tendencyto form complex formation with Fe(III) (Stumm and Morgan,1970). At 10 lg L�1 as the breakthrough, it is evident from Fig. 5that in the case of arsenate a 25% reduction in the volumes treatedwas observed if the concentration of phosphate is at 0.1 mg l�1.However in the case of arsenite, the influence of phosphate wasnot pronounced in the concentration range studied (Fig. 4). In thepresence of 20 mg of silicate around 50% decrease in the volumeof effluent treated was observed for oxyacids of arsenic. In thepresence of a mixture of phosphate and silicate, 50% decrease inthe amount treated effluent was observed for arsenite. However,with arsenate a 70% decrease was observed. To simulate the realground water conditions, experiments were repeated with the lev-els of phosphate, sulfate and silicate similar to that of arsenic con-taminated ground water obtained from Shuklaganj district ofKanpur. It is evident from the figure the results obtained were sim-ilar to that obtained for mixture of phosphate and silicate. Hence it

0 200 400 600 800 1000 1200 1400 16000

Bed Volumes

Co

0.5 mg/l As(III)/As(V)0.5 mg/l As(III)/As(V) + 0.1 mg/l PO40.5 mg/l As(III)/As(V) + 20 mg/l SiO2

0.5 mg/l As(III)/As(V) + 0.1 mg/l PO4 + 20 mg/l SiO2

0.5mg/l As(III)/As(V) +1.5mg/l PO4 + 10 mg/l SiO2+35mg/l SO42-

Fig. 4. Effect of interfering ions on (a) As(III) and (b) As(V) adsorption by ICS.Conditions bed depth 10 cm, flow rate 2 ml/min and pH 7.

10

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once

ntra

tion

of T

otal

Inor

gani

c A

rsen

ic

in th

e ef

fluen

t (ug

/l)

10 cm 20 cm 30 cm

2178 A. Gupta, N. Sankararamakrishnan / Bioresource Technology 101 (2010) 2173–2179

could be concluded that adsorption behavior is not significantly af-fected by the presence of sulfate, however, both phosphate and sil-icate cause interference in the adsorption of arsenic.

3.7. Reusability of the sorbent

Regeneration studies were conducted with three independentcolumns containing IITK ground water spiked with As(V) or As(III)or the mixture of As(V) and As(III).Two sorption–desorption cycleswere performed. Flow rate was maintained at 2 mL min�1 duringsorption and 10 mL min�1 during desorption. The column waspacked with 40.5 g of ICS yielding an initial bed height of 30 cm.As evident from Fig. 5, a decreased breakthrough and in increasedexhaustion time was observed as the regeneration cycles pro-gressed resulting in a broadened mass transfer zone. However, a

0 100 200 300 400

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Desorption

Adsorption

Bed Volumes0 50 100 150 200 250 300 350 400

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(c)

(b)

Desorption

II Cycle

I Cycle

Adsorption

Desorption

Adsorption

250 ug/l As(III) + 250 ug/l As(V)

Con

cent

ratio

n of

tota

l ars

enic

in th

e ef

fluen

t (ug

/l)

Con

cent

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n of

tota

l ars

enic

in th

e ef

fluen

t (ug

/l)

II Cycle

I Cycle

II Cycle

500 ug/l As(V)

(a)

Bed volumes

I Cycle

500 ug/l As(III)

Fig. 5. Adsorption and desorption breakthrough curves of (a) As(III), (b) As(V), (c)As(III) + As(V) for two cycles. Adsorption: Influent As concentration 500 lg/l, pH 7,bed depth 30 cm, Flow rate 2 mL min�1. Desorption: Eluant 0.01 N NaOH, flow rate10 mL min�1.

0 20 40 60 80 100 120 140 1600

C

Bed Volumes

ig. 6. Applicability to arsenic contaminated real life ground water. Conditions: pH, flow rate 2 mL min�1 Conc. of arsenic in the influent – As(III) = 22 lg/l,s(V) = 157 lg/l.

F7A

good metal sorption capacity was obtained in both the cycles. Thedesorption efficiency was found to be around 70% for both arseniteand arsenate species. It was also found that the concentration ofiron in the effluent was <0.2 mg L�1 which indicated the non leach-ability of iron from the adsorbent.

3.8. Applicability of the adsorbent to arsenic contaminated groundwater

The prepared adsorbent was evaluated in fixed bed reactor todecontaminate arsenic. The samples were obtained from Shukla-ganj area of Kanpur district, UP. The characteristics of the watersamples are given in Table 1. It was found that (Fig. 6) 30, 45and 64 bed volumes of water could be treated using the bed heightof 10, 20 and 30 cm bringing down the concentration of arsenic toWHO drinking water standards.

3.9. TCLP leaching test

To validate low arsenic leachability, an extended TCLP test(Isenburg and Moore, 1992) was performed for the arsenic loadedadsorbent. The loaded adsorbent was equilibrated with varying ini-tial pH for 24 h. While the adsorbent had approximately 4780 lgAs/g of dry sorbent, the arsenic concentration in the leachate wasconsistently less than 20 lg in the pH range of 4.8–7.2 (F1 Support-ing information).

4. Conclusions

Iron doped chitosan spacer granules (ICS) were prepared and itssuitability for the removal of both As(III) and As(V) by equilibriumand dynamic conditions at pH 7 were evaluated. Both silicate andphosphate were found to affect the adsorption behavior of arsenic.Recyclability of the adsorbent was demonstrated for two cyclesand the adsorbent was applied for the removal of arsenic from ar-senic contaminated water. TCLP leaching tests revealed the arsenicconcentration in the leachate was consistently less than 20 lg inthe pH range of 4.8–7.2. The applicability at neutral pH in fixedbed column reactors for the removal of both As(III) and As(V) fromreal life ground water samples makes it an attractive adsorbent forarsenic removal filter units.

A. Gupta, N. Sankararamakrishnan / Bioresource Technology 101 (2010) 2173–2179 2179

Acknowledgement

The authors are thankful for the funding provided by Depart-ment of science and Technology, New Delhi under the water tech-nology initiative scheme (DST/TDT/WTI/2KT/22).

Appendix A. Supplementary data

Supplementary data associated with this article can be found, inthe online version, at doi:10.1016/j.biortech.2009.11.027.

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