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Arsenic Removal in Drinking Water—Impacts and NovelRemoval TechnologiesO. S. THIRUNAVUKKARASU a , T. VIRARAGHAVAN a , K. S. SUBRAMANIAN b , O. CHAALAL c & M.R. ISLAM da Faculty of Engineering , University of Regina , Regina, SK, Canadab Product Safety Bureau , Health Canada , Ottawa, Canadac UAE University , City?, UAE, country?d Department of Civil Engineering , Dalhousie University , Halifax, NS, CanadaPublished online: 23 Feb 2007.

To cite this article: O. S. THIRUNAVUKKARASU , T. VIRARAGHAVAN , K. S. SUBRAMANIAN , O. CHAALAL & M. R. ISLAM(2005) Arsenic Removal in Drinking Water—Impacts and Novel Removal Technologies, Energy Sources, 27:1-2, 209-219, DOI:10.1080/00908310490448271

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Energy Sources, 27:209–219, 2005Copyright © Taylor & Francis Inc.ISSN: 0090-8312 print/1521-0510 onlineDOI: 10.1080/00908310490448271

Arsenic Removal in Drinking Water—Impacts andNovel Removal Technologies

O. S. THIRUNAVUKKARASUT. VIRARAGHAVAN

Faculty of EngineeringUniversity of ReginaRegina, SK, Canada

K. S. SUBRAMANIAN

Product Safety BureauHealth CanadaOttawa, Canada

O. CHAALAL

UAE UniversityUAECity?, Country?

M. R. ISLAM

Department of Civil EngineeringDalhousie UniversityHalifax, NS, Canada

Arsenic contamination of surface and subsurface waters has been reported in manyparts of the world; the problem is particularly severe in Bangladesh. In view ofepidemiological problems of arsenic ingestion, it is imperative to look for an effectivetechnology for removal of arsenic in drinking water. Column studies were conducted atthe University of Regina using manganese greensand to remove arsenic from drinkingwater. Iron addition was found to be necessary to achieve effluent arsenic level of25 µg/L in manganese greensand filtration system. In view of the possible regulatoryrequirement to achieve arsenic levels of less than 5 to 10 µg/L, further studies wereconducted using iron oxide-coated sand (IOCS). Batch studies with IOCS showed that

Received May 15, 2001; accepted August 31, 2003.The first and second authors acknowledge major support from Health Canada for this study.

The first author expresses sincere thanks to Dr. Roy Cullimore, Regina Water Research Institute,University of Regina, Regina for providing rusticles and for his advice in the measurement ofbacterial population using BARTTM.

Address correspondence to T. Viraraghavan, Faculty of Engineering, University of Regina,Wascana Parkway, Regina, Sask. S4S 0A2 Canada. E-mail: t.viraraghavan@uregina.ca

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210 O. S. Thirunavukkarasu et al.

effluent arsenic level could be achieved below 5 to 10 µg/L levels. High adsorptioncapacity (136 µg/g) of the IOCS showed that the media could be effectively usedfor achieving less than 5 µg/L of effluent arsenic level in the treatment systems,particularly in small water utilities. A preliminary study was conducted to removearsenic from drinking water using rusticles containing bacteria, and bacterial growthin arsenic solution was also studied.

Keywords adsorption, arsenic, bacteria, filtration, water treatment

Arsenic, a naturally occurring toxic element is mainly present in its inorganic formsin water. Under different pH and oxidation potential of the water, the commonly re-ported arsenic species are arsenite (As(III)), arsenate (As(V)), monomethyl arsenic acid(MMAA) and dimethyl arsenic acid (DMAA). Organic arsenic species are rarely presentat concentrations above 1 µg/L in water supplies (Anderson and Bruland, 1991). Ele-vated concentrations of arsenic in drinking water supplies result from either anthropogenicsources, or weathering of rocks and subsurface materials. Arsenic is the major constituentof at least 245 different minerals (Woolson, 1983), and is mainly present in sulfide min-erals. Igneous and sedimentary rocks contain varying amounts of arsenic. The averageconcentration of As in igneous and sedimentary rocks is 2 mg/kg, and in most rocks itranges from 0.5 to 2.5 mg/kg (Kabata-Pendias and Pendias, 1984).

Arsenic has been recognized as a poison for many years, and it presents seriousproblems to humans and other living organisms because of its toxicity. Ingestion andinhalation or skin adsorption of inorganic arsenic can cause both acute and chronictoxicism in a large number of human organs. Arsenic contamination of surface andsubsurface water has been reported in many parts of the world, and these areas includeSouth-Western Taiwan (Shen, 1973), Southern Thailand (Choprapawon and Rodcline,1997), Inner Mongolia (Luo et al., 1997), China (Niu et al., 1997), West Bengal of India(Chatterjee et al., 1995), Bangladesh (Dhar et al., 1997; Karim, 2000), and NorthernMexico (Cebrian et al., 1983).

A large part of Bangladesh and certain districts of West Bengal, India are facing aserious environmental crisis, where a large population is at a great risk due to arseniccontamination of subsurface waters. The groundwater in seven districts of West Bengalcovering an area of 37000 km2 with a population of 34 million has been contaminatedwith arsenic (Mandal et al., 1998), and many of the tubewells in the affected districtshas arsenic level much higher than 50 µg/L (Mandal et al., 1996). The study conductedby Mazumder et al. (1998) in one of the most affected districts of West Bengal revealedthe prevalence of keratosis and hyperpigmentation among the affected people. Biswaset al. (1998) reported that 45% of the samples collected from 41 districts out of 64 inBangladesh contains above 50 µg/L of arsenic in drinking water. The source of arseniccontamination of surface and subsurface waters in Bangladesh is believed to be geolog-ical, but the exact source and mechanism of arsenic leaching into groundwater is stillunder debate.

Various treatment processes such as coagulation-precipitation, adsorption onto acti-vated alumina, reverse osmosis and ion exchange have been reported in the literature toremove arsenic from drinking water (Viraraghavan et al., 1992). The selection of appro-priate treatment process for a specific water supply will depend on many factors suchas concentration of arsenic, source water composition of other constituents, pH and costeffectiveness. The maximum contaminant level for arsenic in drinking water in the UnitedStates is set at 10 µg/L (USEPA, 2001). Because of cancer risks, Canada has already

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Arsenic Removal in Drinking Water 211

lowered this level to 25 µg/L (Viraraghavan et al., 1999). The objective of this researchwas to develop the best technological option through a series of laboratory studies so asto achieve a low level of arsenic (less than 10 µg/L) in finished water supplies. Columnstudies were conducted with manganese greensand to examine the removal of arsenicin drinking water. Batch isotherm studies were conducted using iron oxide-coated sand(IOCS) to study the removal of As(III) in water. Studies were conducted to examinearsenic removal using rusticles containing bacteria. Bacterial growth in arsenic solutionwas also studied to explore the possibility of concentrating arsenic and removing thesebacterial clusters by separation processes.

Materials and Methods

Tap water was used as the raw water source for most of the experiments. The physico-chemical characteristics of the water are given in an earlier publication (Viraraghavanet al., 1999). Manganese greensand was purchased from Watergroup Canada Ltd., Regina.The physico-chemical characteristics of the greensand and conditioning details are pro-vided in earlier publications (Viraraghavan et al., 1999; Subramanian et al., 1997). Arsenicoxide stock solution (1 mL = 1 mg As) purchased from Fischer Scientific, Edmonton wasused, and the required working standards were prepared daily from the stock solution. Aportable pH meter [Hanna Checker 1 (Sigma chemical, Ontario)] was used to measurethe pH. The accuracy of the pH meter was ± 0.2 pH unit.

The redflint sand used in the preparation of iron oxide coated sand (IOCS) waspurchased from Watergroup Canada Ltd., Regina. The sand was sieved to a geometricmean size of 0.6 mm to 0.8 mm, acid washed (pH 1; 24 h), rinsed with distilled waterthree times and dried at 110◦C for 20 hours before use. IOCS was prepared similar tothat of the procedure mentioned by Edwards and Benjamin (1989). In the preparation ofcoated sand, Fe(NO3)3.9H2O (BDH Inc. Toronto) solution was used and effective coatingwas achieved through a high temperature coating process.

A column 10 cm in diameter and 180 cm high was used in the studies. Tap watersupplemented with required concentrations of As(III) and Fe was pumped into the columnusing a submersible pump (model #3E-12NT, Little Giant Pump Co., Oklahoma). In thefirst set of experiments tap water spiked with Fe:As(III) solution at a ratio of 20:1 waspumped into the column at a flow rate of 0.83 L/m (117 m3/m2/d). The initial As(III)concentration was kept at 100 µg/L. The packed volume of manganese greensand in thecolumn was 4681 mL and the empty bed contact time was 5.64 minutes. In the secondset of experiments, Fe:As(III) ratio was kept at 7:1 and the initial As(III) concentrationwas 50 µg/L. Potassium permanganate was continuously fed into the column to oxidizethe Fe(II), Mn(II) and As(III), and to generate the column. The requirement of KMnO4was calculated on its stoichiometric requirement to oxidize Fe(II), Mn(II) and As(III),and the details are available elsewhere (Viraraghavan et al., 1999).

Rusticles containing bacteria used in the batch experiments were obtained from theRegina Water Research Institute, University of Regina, Regina. A simple batch kineticstudy was performed with rusticles in which one gram of rusticles was added to 1 L oftapwater in a beaker spiked with an initial As(III) concentration of 100 µg/L. The beakerwas covered with parafilm and perforations were made in the parafilm for the transferof atmospheric air into the solution. Air was injected into the solution continuouslythroughout the experiment through the air outlet. The experiment was conducted for29 days, and samples were withdrawn by a syringe at regular intervals and arsenic wasanalyzed.

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Biological activity reaction test (BARTTM) was conducted to determine the microbialpopulation in the rusticles. The test detects the activity (aggressivity) of the bacteria bythe time lag (TL, measured in the number of days from the start of the test to whena reaction is observed). The longer the TL before the observation of activity, the lessaggressive the bacteria are in that particular sample (Cullimore, 1998). The bacteriathat were tested using BARTTM included iron related bacteria (IRB), sulfate-reducingbacteria (SRB), heterotrophic aerobic bacteria (HAB), slime-forming bacteria (SLYM),denitrifying bacteria (DN), and fluorescing Pseudomonas (FLOR).

A separate study was conducted to study the growth of the thermophillic bacteriain arsenic solution. The growth medium was prepared in 10 mL sterilized tubes. Eachtube contained 0.5 mL of indigenous bacterial solution and 2 g of nutrient broth. Themedium was gently mixed and exposed to different temperature conditions. Higher bac-terial growth rate was observed distinctly at 80◦C. In one of the compartments equippedwith a stirrer located in a bioreactor, the bacterial cultures were mixed with 10 mg/L and20 mg/L arsenic solutions and their growth rate was studied. An image analysis system(IAS) consisting of a high-resolution video camera mounted on an optical microscopeand an image processor was used to count the bacteria. The image was visualized with thevideo camera through a microscope lens. The details of the method are given elsewhere(Kaleli and Islam, 1997).

The instrument used in this study was Varian type SpectrAA—600 Zeeman GFAASequipped with GTA 100—graphite tube atomizer and PSD—100 programmable sampledispenser. Epson® FX-870—(9) pin dot matrix printer was used to print the analyti-cal results as well as signal graphs. Argon gas of ultrahigh purity (99.995%) (PraxairProducts Inc, Ontario) was used to sheath the atomizer and to purge internally. Nickelnitrate solution at 50 mg/mL or Palladium solution at 1000 µg/mL or 0.1% (v/w) MgNO3.6H2O or a combination of these solutions at 5–7 µL was used as matrix modifiers forcalibration.

Results and Discussion

Column Studies with Manganese Greensand

Results of column studies were analyzed using the Thomas equation to evaluate themaximum solid phase concentration (q0) and the Thomas rate constant (k). The Thomasequation is as shown below (Reynolds and Richards, 1996):

Ce

C0= 1

1 + exp

[k

Q(q0m − C0V )

]

The data from the column studies were subjected to non-linear estimation on “Statisticafor windows package” (release 5.1 ’97 edition). The predicted values of Ce/C0 by theThomas model were compared with the observed values and Figure 1 shows the plot ofthroughput volume (V ) with Ce/C0. Table 1 shows the summary of results from columnstudies. In the case of Fe:As(III) ratio of 20:1, the maximum solid phase concentrationq0 was estimated at 22.3 µg/g based on the weight of manganese greensand; whereas q0was estimated at 2.5 µg/g for Fe:As(III) ratio of 7:1. It was quite clear from these resultsthat iron addition enhanced removal in the column studies using manganese greensandas a filtration media.

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Arsenic Removal in Drinking Water 213

Figure 1. As(III) removal in column studies using manganese greensand.

Table 1Summary of the results for the removal of As(III) by manganese

greensand (MGS) in column studies

Manganese greensand

Arsenic concentration (µg/L) 100 50Fe:As 20:1 7:1Flow rate (L/min) 0.83 0.83Volume of MGS (L) 4.681 4.681EBCT (minutes) 5.64 5.64Total throughput volume (L) 1440 2168“k” (mL/min.µg) value from Thomas model 0.83 1.66Maximum solid phase concentration qo (µg/g) 22.3 2.5

from Thomas model

Isotherm Studies with Iron Oxide-Coated Sand (IOCS)

Isotherm studies were conducted by varying the mass of IOCS to remove 100 µg As(III)/Lspiked in tap water. The experiment was conducted at a room temperature of 22 ± 1◦Cand the results showed that a maximum arsenic removal of 95.8% (4.2 µg As(III)/L)was obtained in batch studies. The well known isotherms, namely the Langmuir, theFreundlich and the BET isotherms, were used to describe the adsorption. The isothermequations are as follows:

The Freundlich:

x

m= KC

1n

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The Langmuir:

x

m= Q0bC

1 + bC

The BET:

x

m= AXmC

(Cs − C)

(1 + (A − 1)

C

Cs

)

The data was subjected to non-linear estimation using a statistical software (StatsoftInc., 1997), and simplex method was used to solve the equations. The predicted valuesby the model were plotted with the concentration of As(III) remaining in solution, andis shown in Figure 2. The model equations for all the isotherms are shown in Table 2.

The convex nature of all the isotherms suggests a favorable arsenic adsorption byIOCS. The separation factor, R of 0.346 (O < R < 1) estimated from the Langmuirconstant indicated that arsenic adsorption can be modeled by the Langmuir isotherm. The‘b’ value from the Langmuir equation showed that 131.6 µg of arsenic was required tocompletely saturate 1 gram of IOCS. The Freundlich constants, K and n, were estimatedto be 3.7 (L/µg) and 1.35, respectively. The high ‘K’ value and a high ‘A’ (7.6) valuein the BET isotherm indicated that the adsorption capacity of the IOCS was very high.Low 1/n value (0.74), suggested that any large change in the equilibrium concentrationof arsenic would not result in a change in the amount of arsenic taken by the IOCS. Thedata fitted well with the BET isotherm and it showed that multilayer adsorption mightalso be involved in arsenic removal. The correlation coefficients for all the isothermswere high representing a good fit of the observed data. The t-test showed that all theconstants were statistically significant at 95% confidence level for all the isotherms. The

Figure 2. Isotherms for As(III) adsorption on to IOCS.

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Arsenic Removal in Drinking Water 215

Table 2Isotherm equations for As(III) removal using IOCS from non-linear estimation

CorrelationIsotherm Equation coefficient, r

Freundlich X/M = 3.72C(1/1.35) 0.98a

Langmuir X/M = (0.02 × 132 × C)/(1 + .02C) 0.98a

BET X/M = (7.6 × 40.7 × C)/((100 − C)(1 + (7.6 − 1)C/100)) 0.97a

aIndicates that the parameters estimated are statistically significant (t-test) at 95% confidencelevel.

adsorption capacity of the IOCS was estimated at 136 µg/g, which indicated a highadsorption capacity of the IOCS.

Batch Studies with Rusticles

The results showed that the minimum concentration of As(III) achieved in the aboveexperiment was 33.2 µg/L on the 29th day; if samples were collected and analyzed after29th day, the arsenic level in the solution might have dropped down to less than 25 µg/L.

Ho (1996) pseudo second order model shown below was used to analyze the biosorp-tion data obtained.

t

q= 1

2kq2e

+ t

qe

The above equation is rearranged as follows:

q = 2kq2e t

1 + 2kqet

The experimental data was subjected to non-linear estimation using Ho model, andthe predicted values by the model with time are shown in Figure 3. It was found that theadsorption capacity was higher than that of manganese greensand but less than that ofiron oxide-coated sand. The results of BARTTM and bacterial population in the rusticlesare shown in Tables 3 and 4. The results showed that the populations of both SRB, andIRB in the rusticles were high, and were mainly responsible in the mechanism of arsenicremoval.

The growth of thermophillic bacteria in As solution with time is shown in Figure 4.The results showed that bacteria was found to grow well in 20 mg/L As solution. Thebacteria formed clusters that can concentrate arsenic; these clusters can be removed byseparation process such as microfiltration. In a similar study reported by Phillips andTaylor (1976), the growth of Alcaligenes faecalis occured in arsenic solution and theorganisms were capable of oxidizing arsenite into arsenate in the solution.

Conclusions

1. Batch study results demonstrated that iron oxide coated sand (IOCS) was foundto be the best media in removing arsenic below 5 to 10 µg/L levels.

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Figure 3. As(III) removal in the kinetic studies using rusticles.

Table 3Results of the BARTTM for rusticles

Time lag (days)

Bacteria 1 2 3 4 5 6 7 8 9 10

IRB —a — — — + a(BC)b −−−−−−−−−−−−−−−−−−−−−−−−→SRB — — — — + (BA) −−−−−−−−−−−−−−−−−−−−−−−−→HAB — — — — — — + (DO) −−−−−−−−−−→DN — — + (FO) −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−→SLYM — — — — + (FO,CL,DS) −−−−−−−−−−−−−−−−−−−−−−−−→FLOR — — — — — — — — — —

a−Negative, +Positive.bReaction code: BC—brown cloudy; BA—blackened base and top; DO—bleaching from top;

FO—foam around ball; CL—cloudy growth; DS—dense slime.

Table 4Bacterial population in rusticles

Colony forming units Colony forming unitsPossible log per mL (cfu/mL) per mL (cfu/mL)population for 0.1 g for 1 g

Bacteria Aggressivity (PLP) (rusticles) (rusticles)

IRB Medium 3 1,000–5,000 10,000–50,000SRB High 3.6 5,000–10,000 50,000–100,000HAB Low 1 10–100 100–1,000DN Medium 3 1,000–5,000 10,000–50,000SLYM Medium 3 1,000–5,000 10,000–50,000

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Arsenic Removal in Drinking Water 217

Figure 4. Bacterial growth in arsenic solution.

2. Manganese greensand was found to be efficient in removing arsenic to a levelbelow 25 µg/L. Iron addition enhanced arsenic removal in filtration studies.

3. A preliminary study using rusticles containing bacteria showed promise. Furtherstudies are necessary.

4. Growth of thermophillic bacteria in arsenic solution showed that removal of ar-senic by colonies of thermophillic bacteria is possible. Separation processes needto be investigated further.

Nomenclature

x mass of solute adsorbed (µg)m mass of adsorbent (g)b a constant related to the energy or net enthalpy of adsorption (L/µg)Q0 mass of adsorbed solute completely required to saturate a unit mass of adsorbent

(µg/g)C equilibrium concentration (µg/L)K an experimental constant indicative of the adsorption capacity of the adsorbent

(L/µg)n an experimental constant indicative of the adsorption intensity of the adsorbentCs the saturation (initial) concentration of the solute (µg/L)A a constant related to the energy of interaction between the solute and the adsor-

bent surface; A negative value indicates a minimum or no adsorption. A highvalue indicates a high adsorption of the adsorbate

Xm a constant related to the amount of solute adsorbed in forming a complete mono-layer (µg/L)

k Thomas rate constant (L/min.µg)Ce effluent adsorbate concentration (µg/L)C0 influent adsorbate concentration (µg/L)q0 maximum solid phase concentration of the solute (µg/g)V throughput volume (mL)Q volumetric flow rate (mL/min)qe the amount of adsorbate at equilibrium (µg/g)q the amount of adsorbate adsorbed at any time ‘t’ (µg/g)

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