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Groundwater Quality: Natural and Enhanced Restoration of Groundwater Pollution (Proceedings ofthe Groundwater Quality 2001 Conference held at Sheffield, U K , June 2001). I A H S Publ. no. 275, 2002.

391

Technique for arsenic removal from groundwater utilizing geological options—an innovative low cost remediation

R. B H A T T A C H A R Y Y A , D. C H A T T E R J E E University of Kalyani, Kaiyani, Nadia 741235, West Bengal,

India

e-mail: bhattacharvva rupa@,hotmail,com or rupa(S),aom.kth.se

G. J A C K S Department of Civil and Environmental Engineering, Division of Land and Water Royal Institute of Technology KTH, Stockholm, Sweden

Resources.

S. S. D E D A L A L River Research Institute, Harynghata,

West Bengal,

India

Abstract High arsenic levels in groundwater have emerged as a nagging problem in recent decades in different parts of the world. The high arsenic groundwater of the Holocene aquifers of the alluvial terrain of the Bengal Delta Plain (BDP) is unique and elusive in the extent of its exposure causing a threat to the lives of more than 70 million people. The present paper deals with the utilization of the indigenous geological material, latérite (or red earth) for removing arsenic from groundwater and potable water supplies. The aim is to devise a low cost arsenic filter unit using latérite. The material has been manipulated in several ways to study its applicability as an effective arsenic adsorbent. The results exhibit a removal efficiency of >90% and therefore can be implemented as an effective arsenic filter unit. Cost analysis shows that production of 101 of water containing arsenic concentration as per WHO guidelines will cost US$ 0.625. Key words arsenic; arsenic adsorbent; cost effective; latérite; technical feasibility

INTRODUCTION High arsenic groundwater has lethal impacts on human health after prolonged consumption and is therefore a grim environmental problem. Cases of arsenic toxicity has been reported from several parts of the world, viz. Argentina, China, Taiwan, Thailand, Mexico, USA, Ghana, Hungary, UK, Chile, N e w Zealand and Russia. However, the vast Holocene alluvial aquifers of the Bengal Delta Plain (BDP) (lat. 2 1 3 0 ' N - 2 7 1 0 ' N ; long. 86°E-90°E) (Bhattacharya et al, 1997) comprising parts of West Bengal, India and Bangladesh, is demarcated as the worst affected area in the context of arsenic poisoning in groundwater (ACIC, 1998). The alluvial tracts of eight districts (Malda, Murshidabad, Nadia, Burdwan, Howrah, Hooghly, North and South 24 Parganas) of West Bengal, India are affected with high arsenic groundwater causing the health of more than thirty million people to be at risk (Mandai et al 1996; Bhattacharya et al, 1997, 1998). Manifestations of arsenical dermatosis, hyperkera­ tosis, cirrhosis, portal fibrosis, pigmentation of palms and soles, melanosis and skin cancer (Chakraborty et al, 1987) are reported among the affected rural population. o

o

392

R. B h a t t a c h a r y y a e t al.

Groundwater resources have been used exhaustively in the region over the last three decades to meet the need for sufficient drinking water supply for the everexpanding population in a region with poor inff astructural facilities, as well as the green revolution. The uncontrolled and uncoordinated development of groundwater exacerbates the effects of the elevated level of arsenic in groundwater.

PROBABLE HYPOTHESES Two hypotheses have been proposed to explain the origin and occurrence of dissolved high arsenic concentration in the groundwater: (a) the arsenic derives from the oxidation of pyrites/arsenopyrites in the aquifers as a result of over extraction of groundwater for irrigation for high delta paddy cultivation as well as to meet the drinking water crisis of over population (Das et al, 1996) and consequent aquifer dewatering; (b) the desorption of ferric hydroxide minerals present as coatings in the aquifer sediments under reducing groundwater conditions results in the co-dissolution of arsenic from sediment to groundwater. The anaerobic conditions of the affected sedimentary aquifers can be visualized by the moderately low Eh data, low to very low dissolved oxygen content, and high dissolved iron (Fe(II)) concentration in groundwater ( R G N D W M , 2000; Bhattacharya et al, 1997; Nickson et al, 1998, 2000). The low nitrate and sulphate content as well as presence of total organic carbon may perhaps facilitate the above process ( R G N D W M , 2000). Research work carried out so far reveals that the reductive dissolution of ferric hydroxide is predominant in the sedimentary aquifers mobilizing arsenic in groundwater normally with soluble iron, Fe(II), phases.

A L T E R N A T I V E S FOR SAFE DRINKING W A T E R SUPPLY Several remedial options adopted, as well as implemented, in the action plans for the supply of potable water, did not yield promising results in the long run. The adsorption-desorption phenomenon of arsenic in the natural environment is greatly influenced by the insoluble Fe(III)-soluble Fe(II) phase. Therefore, social acceptability, technical feasibility and economy of the remedial option(s) need to be critically scrutinized prior to the implementation for the long-term action plan of community water supply scheme in the rural and semi urban areas.

L O W COST R E M E D I A T I O N OPTION The present contribution deals with a study on the use of geological material, latérite— the red earth (Fitzpatrick et al, 1983). Latérite (later => brick) (Buchanan et al, 1807) is a kind of indurated vesicular rock with highly ferruginous Fe(III) deposits and full of pores and cavities. Plausible reactions for adsorption of an anion on latérite are: +

+

SOH(s) + Ff (aq) = S O H ( s )

(1)

2

+

0

1y

S O H ( s ) +A"'(aq) = SA " (s) + H 0(1) where S refers to the soil adsorbent. 2

2

(2)

Technique for arsenic removal from groundwater: innovative low cost remediation

393

The p H (point of zero charge) of latérite on the basis of acid-base titration is found to be 8.5. Identical amounts of 5 g unsized crushed latérite (Medinipur) samples were subjected to different strengths of HC1, HAc, as well as N a O H washings respectively and the p H of each washed variety was recorded. Identical portions of 100 ml of solutions containing an initial concentration of 250 pg 1"' As(V) were added to each of the modified latérite varieties and the samples are shaken for 24 h to attain equilibrium. Solutions were then filtered through 0.2 p m polycarbonate filter and the final arsenic concentration was measured in each case. The pH of groundwater in the BDP varies between 6.5 and 7.5. Therefore latérite can perform efficiently in adsorbing arsenic over a wide p H range. z p c

GEOCHEMISTRY OF LATERITE Latérite is a vesicular clayey residuum of intensive chemical weathering of a wide variety of rocks under strongly oxidizing and leaching conditions occurring typically in tropical regions. The predominance of iron generally gives the rock its typical red colour. The major components in latérite are iron, aluminium, silicon, manganese, nickel and titanium in the form of hydroxides and/or oxides. Ferruginous, bauxitic and nickel type varieties are the most commonly found types of latérites. Latérite is an acidic soil with a typical p H between 4 and 5. Both hydrous iron and aluminium oxide components in latérite have a p H at 8.5-8.6 (Anderson et al, 1976; Kinniburgh et al, 1976). Hydrous Fe- and Al- oxyhydroxide components of latérite, are characterized by a high positive surface charge at a wide pH range and therefore act as an adsorbent for several anionic contaminants (Pierce & Moore, 1982). Both oxy anionic arsenate and arsenite species have a strong tendency to adsorbtion on the oxide surfaces of latérite at a wide range of p H (Pierce & Moore, 1982). z p c

The log k values for the adsorption of the different pentavalent arsenic ions as well as trivalent arsenic species are cited below: =FeOH° + A s 0 " + 3 H 3

+

= =FeH As0 ° + H 0

log k = 29.31 ± 1.02

(3)

3

+

= =FeHAs0 " + H 0

log k = 23.51 ± 0 . 1 8 log k = —

(4)

log k = 13.57 ± 0 . 0 6 log k = 5.41 ± 0 . 1 5

(6)

2

4

=FeOH° + A s 0 ~ + 2 H 4

=FeOH° + A s 0 " + H 3

4

2

4

2

2

= =FeAs0 " + H 0

+

4

4

2

3

=

=FeOH° + A s 0 "

3

= =FeH As0 ° + H 0

4

=Fe0HAs0 ~

3

=FeOH° + A s 0 ~

4

2

3

3

2

(5) (7)

The surface species =FeAs0 "~ probably has no impact on the surface complexation of latérite. In the present study the ferruginous variety of latérite, popularly called the red earth, from Medinipur in West Bengal, were used for the batch experiments. The results reveal that the finer grains (Fig. 1) have the greatest adsoiption area; nevertheless the unsized variety also has effective adsorption sites revealing the material to be porous in nature. Moreover, though the acid treated variety exhibits the greatest surface area for adsorption (Fig. 1), the ordinary variety is an efficient arsenic adsorber too due to the porous nature of the material. The unsized soil variety can be therefore be used for commercial purposes instead of the fine variety which is labour intensive to prepare. The effect of time on the adsorptive capacity of latérite is 4

394

R. Bhattacharyya

Distilled water

acid

100%

et al.

fine medium

80% 60% 40% -| 20% 0%

U-l-

ordinary

Tap water

ordinary '2 S O m

Fig. 1 Effect of washing and grain size on adsorption.

350

150 Set 4

Set 5

Fig. 2 Effect of time on arsenic adsorption.

presented in Fig. 2. The results reveal that the difference between the first 10 min and several hours thereafter does not significantly affect the capacity. The adsorption process is highly effective during the first few minutes. Figure 3(a) and (b) reveals a good correlation between adsorbed arsenic and iron in the treated latérite both under stirred and unstirred conditions. The stirring effect probably resulted in a greater scope for contact between the soil-solution surface. Groundwater samples of initial pH 7.02 and initial total arsenic concentration 111.1 u,g l" , were manipulated with HC1 and N a O H to the desired pH values of 1-12. Latérite was added to the solutions, stirred for 1 min and left for one hour. The results are shown in Fig. 4. This reveals that latérite acts efficiently in adsorbing arsenic over a wide range of pH. However, under strongly acidic conditions the soil itself gets dissolved thereby decreasing its efficiency. Under strong alkaline conditions the iron content of latérite itself gets precipitated and a sharp fall in adsorbing capacity occurs. Latérite adsorbs As(V) predominantly at pH 4 - 5 whereas As(III) is effectively adsorbed at neutral pH. 1

A reasonable fall in the adsorbing efficiency in the above experiment at pH 4 - 5 indicates that As(III) is predominant in the BDP groundwater. The results obtained from a simple earthenware pitcher containing latérite as the filter media reveal that in addition to the adsorption of arsenic, latérite also plays a significant role in decreasing the amount of dissolved iron. The MnC>2 as well as TiC>2 content of the latérite probably facilitate the oxidation of the dissolved iron and arsenic content of the groundwater. The results are tabulated in Table 1.

Technique for arsenic removal from groundwater: innovative low cost remediation

(a) \ /

~ . .. . . . . Relation b e t w e e n a d s o r b e d arsenic a n d i r o n . . ^ . , , in t h e treated latente u n d e r u n s t i r r e d L

L

395

relation between adsorbed arsenic and . , , ., . . i r o n in t h e treated latente u n d e r s t i r r e d .... conditions

(h) \ / w

t

J

condition

t

3500

3000

y = 797.79x- 1102.9 2

R = 0.6693 2500 y = 7 3 2 . 1 9 X - 1154.4

2000

2

R = 0.9108 1500

1000

500

0 0 [Asjin ug/kg

[As] in u g / k g

Fig. 3 Relationship between adsorbed arsenic and iron in treated latérite under unstirred (a), and stirred (b) conditions.

100 «80-| >

1

3

60 /•

A A

M

S? 20 1

2

3

4

5

6 PH

7

8

9

i

10

Fig. 4 Groundwater arsenic adsorption on latérite as a function of pH.

Table 1 Experimental results of pilot scale study using an earthenware pitcher impregnated with fixed bed latérite media. 1

Trial run

Initial [As] (mg 1"')

% As removal

Initial [Fe}, (mg l" )

% Fe removal

1 2 3 4 5 6

0.133 0.263 0.168 0.017 0.263 0.229

88 97 94 41 96 96

2.875 2.623 0.143 3.501 0.143 1.934

71 78 84 91 69 95

T

ECONOMIC ASPECTS Latérite is an indigenous natural material abundantly available in India. The cost calculated for the transportation of latérite approximates to about US$1.5 per 10 k g

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R. Bhattacharyya et al.

latérite per km. The treatment process is estimated to cost about US$0.625 to produce ten litres of water containing arsenic concentration as per W H O guidelines. Therefore fixed bed latérite can be successfully employed on a large scale for removal of arsenic from groundwater.

A c k n o w l e d g e m e n t s The first author duly acknowledges the financial support from the Swedish Institute which facilitated her participation in the GQ 2001 conference.

REFERENCES AC1C (1998) West Bengal and Bangladesh: Arsenic Crisis Information Center. URL: http://wso.net/wei/dch/acic/index.html. Anderson, M. A., Ferguson, .1. F. & Gavis, J. (1976) Arsenate adsorption on amorphous aluminium hydroxide. J. Colloid Interface Sci. 54, 391 -399. Bhattacharya, P., Chatterjee, D. & Jacks, G. (1997) Occurrence of arsenic contaminated groundwater in alluvial aquifers from Delta Plains, Eastern India: options for safe drinking water supply. Int. J. Water Res. Manage. 13( 1 ), 79-92. Bhattacharya, P., Larsson, M., Leiss, A., Jacks, G., Sracek, A. & Chatterjee, D. (1998) Genesis of arseniferous groundwater in the alluvial aquifers of Bengal Delta Plains and strategies for low-cost remediation. In: Abstract Volume, International Conference on Arsenic Pollution of Groundwater in Bangladesh: Causes. Effects and Remedies (Dhaka, Bangladesh, February, 1998), 120-123. Buchanan, F. (1807) A Journey from Madras Through the Countries of Mysore, Cunura and Malabar vol. 2, 436-467. London, UK Chakraborty, A. K., Banerjee, D., Ghosal, S. & Barman, P. (1987) Arsenical dermatitis from lubewell water in West Bengal. Indian J. Medical Res. 85, 326-334. Das, D., Samanta, G., Mandai, B. K., Chowdhury, T. R., Chanda, C. R., Chowdhury, P. P.. Basu, G. K., Chakraborli. D. (1996) Arsenic in groundwater in six districts of West Bengal, India. Environ. Geochem. and Health 18, 5-15. Fitzpatrick, E. A. (1983) Soils: Their Formation, Classification and Distribution. Longman, London, UK. Kinniburgh, D. G., Jackson, M. L. & Syers, J. K. (1976) Adsorption of alkaline earth, transition and heavy metals by hydrous oxide gels of iron and aluminium. Soil Sci. Soc. Am. J. 40, 796-799. Mandai, B. K., Roy Chowdhury, T., Samanta, G., Basu, G. K., Chowdhury, P. P., Chanda, C. R., Lodh, D., Karan, N. K., Dhar, R. K., Tamil i, D. K., Das, D., Saha, K. C. & Chakraborti, D. (1996) Arsenic in groundwater in seven districts of West Bengal, India: the biggest arsenic calamity in the world. Current Science 70(11), 976-986. Nickson, R., McArthur, J., Burgess, W., Ahmed, K. M., Ravenscrofl, P. & Rahman, M. (1998) Arsenic poisoning of groundwater in Bangladesh. Nature 395, 338. Nickson, R. T., McArthur, J. M., Ravenscrofl, P., Burgess, W. G. & Ahmed, K. M. (2000) Mechanism of arsenic release to groundwater, Bangladesh and West Bengal. Appl. Geochem. 15(4), 403-413. Pierce, M. L. & Moore, C. B. (1982) Adsorption of arsenile and arsenate on amorphous iron hydroxide. Water Res. 16, 1247-1253. RGNDWM (2000) Mechanism of Mobilization of Arsenic in Sedimentary Aquifers in West Bengal and Realistic Approach for In-Silu Remedialion Methods. Report from the project funded by Rajiv Gandhi National Drinking Water Mission, Ministry of Rural Development, Government of India. Department of Chemistry, Kalyani University, Nadia, India.