NATURAL ARSENIC IN GROUNDWATER: OCCURRENCE, REMEDIATION AND MANAGEMENT - CHAPTER 29 doc

A simple and environmentally safe process for arsenic remediation – laboratory and field evaluation Kshipra Misra, M.T. Companywala, Sanskriti Sharma, Alips Srivastava & P.C. Deb Naval Materials Research Laboratory (NMRL), DRDO, Ministry of Defence, Addl. Ambernath, India ABSTRACT: This paper reports the results of laboratory and field evaluation of a simple and envi- ronment-friendly arsenic removal filter. The filter works on the simple principle of co-precipitation and adsorption followed by filtration through treated sand. An easily available processed waste of steel industry is used as a reactive medium in the filter. Laboratory trials of the filter have suc- cessfully been completed. Prototype filters are installed for field trials in the arsenic-affected villages of West Bengal and have been reported to be successfully operating. Salient features of the filter include its cost-effectiveness, and easy operation and maintenance, involving only normal washing and replacement of the media. It is suitable for household use and requires no energy source. The waste generated can be converted into non-leachable cement matrix of M-25 standard grade impermeable concrete blocks used in construction industry. This makes the system eco- friendly. The unit flow rate of capacity 15 L/h and 30 L/h filtered water and quality conform to the drinking water standards for arsenic and iron. 1 INTRODUCTION An alarmingly large population of India and Bangladesh, 66 million in the Gangetic belt of India and 79.9 million in Bangladesh (Bose & Sharma 2002, Ahmed et al. 2004) is exposed to arsenic poi- soning due to continuous usage of arsenic-contaminated ground water. Arsenic concentration in the water of these regions above the permissible limit (Chakraborti et al. 2003, USEPA 2001, 2004). Arsenic contamination of groundwater in these areas has mainly occurred due to natural reasons (Bose & Sharma 2002, Ahmed et al. 2004). According to the most accepted and most plausible theory, in the Late Pleistocene/ Holocene period, iron and arsenic-bearing minerals in upstream of the Ganges river belt may have undergone oxidation due to exposure to atmosphere during erosion, resulting in subsequent mobilization of arsenic and iron downstream. The mobilized iron got pre- cipitated as iron oxy-hydroxide and arsenic got either adsorbed onto or co-precipitated with iron oxy-hydroxide. These arsenic containing precipitates then got deposited in the Gangetic delta region in the form of iron oxy-hydroxide coating on aquifer sediments. In the present day situation, reducing conditions prevailing in the sub-surface environment is causing dissolution of this coating and mobilization of adsorbed/co-precipitated arsenic (Bhattacharya et al. 1997, Nickson et al. 1998, 2000, McArthur et al. 2001. Most of the affected people in the subcontinent are poor villagers and so the commonly available expensive technologies become economically non-viable. More so, the delicacy of these technolo- gies and the subsequent operation and maintenance (Zaw et al. 2002, Katsoyiannis et al. 2002) add to their expenses, apart from being inconvenient to be used by villagers. Considering that a large population at risk, there is an urgent need to develop ways to mitigate this problem by reducing the level of arsenic in drinking water to tolerable limits through easy and inexpensive means. The arsenic removal filter reported here is designed to provide a low cost, easily available, eco-friendly arsenic removal system for the rural people. 273 Natural Arsenic in Groundwater: Occurrence, Remediation and Management – Bundschuh, Bhattacharya and Chandrasekharam (eds) © 2005, Taylor & Francis Group, London, ISBN 04 1536 700 X Copyright © 2005 Taylor & Francis Group plc, London, UK 2MATERIALS AND METHODS The reactant material (media), a processed waste from Steel industry, has been obtained from M/s Tata Wires Ltd., Mumbai. Sand used has been obtained from the riverbank of River Yamuna in Delhi, India, and from the riverbank of River Ganga in Kolkata, India. Fine cloth filter has been procured from a local cloth merchant in Mumbai. AR quality reagents and Milli-Q grade water have been used for solution preparation. Solutions of As ϩ3 and As ϩ5 have been prepared using corresponding salts, NaAsO 2 and Na 2 HAsO 4 и 7H 2 O, respectively. Mixture of As ϩ3 and As ϩ5 (in the ratio of 1:1) has been prepared by dissolving equimolar amount of corresponding salt in Milli-Q grade water. The reactant material is soaked overnight in water before using in the filter. The sand used is subjected to physical treatment (washing and heat treatment) prior to using it in the arsenic removal filter. The reactant material and sand have been characterized for their surface area and composition using Micromeritics ASAP 2010 Surface Area Analyzer at Centre for Fire, Environment and Explosives Safety (CFEES), Delhi, and by Phillips X-ray fluorescence (XRF) at Durgapur Steel Plant, Durgapur, respectively. The surface texture of the reactant material was carried out on Scanning Electron Microscope (Model: Leo 1455). 2.1 Metal analysis The variation in the pH of pure water and of arsenic solution when allowed to percolate down through the reactant material and through sand has been determined using a pH meter (Model: Elico LI-120). Arsenic concentration in water, prior to and after treatment, has been measured as per ASTM method (ASTM D 2972-88) using Hydride Generator (Model: HG-3000) attached to AAS (Model: GBC 904AA) at Centre for Fire, Environment and Explosives Safety (CFEES), Delhi, India. Iron concentration was also determined using same AAS. 2.2 Design of arsenic removal filter Arsenic removal filter (Fig. 1) has been designed and fabricated both in plastic and in stainless steel. Two filter systems have been designed and evaluated, one operating at a flow rate of 15 L/h and the other operating at a flow rate of 30 L/h. 2.3 Waste disposal Although the waste generated during arsenic removal process is not environmentally harmful as such, as reported by earlier workers, yet disposal of arsenic-laden waste is an important aspect under growing environmental regulations. Therefore, precipitate formed during reaction and the used sand is being disposed off in the form of impermeable concrete blocks of M-25 (Singh, 1982) standard grade used in construction industry resulting in no waste generation in the process and making the technology environment-friendly and green. 3 RESULTS AND DISCUSSION 3.1 Characteristics of the reactant material Scanning electron micrograph (Fig. 2) of the material at 500 times magnification shows the fibrous elongated morphology. Characteristics of the reactant material and sand (Table 2) clearly indicate that the reactant material is nothing but 99% iron and acts as zero-valent iron. Surface area value of sand indicates that its adsorption capacity is low and is basically functioning as a fine filter in this process. The arsenic removal filter, therefore, works on the simple principle of co-precipitation of arsenic with iron and adsorption of this precipitate on iron oxyhydroxides (Su et al. 2001, Manning et al. 274 Copyright © 2005 Taylor & Francis Group plc, London, UK 2002, Melitas et al. 2002, Nikolaidis et al. 1998), followed by filtration through treated sand. Probable reactions involved in the process are as given below: (1) (2) Sodium salts of arsenite and arsenate get ionized in aqueous solution. Both arsenite and arsenate oxyanions are removed further by co-precipitation (as FeAsO 4 and FeAsO 3 ) and by adsorption onto ferric oxyhydroxide solids. The same has been reported by a number of workers earlier also (Su et al. 2001). 275 Figure 1. Schematic diagram of arsenic removal filter. Explanations: 1: Inlet for arsenic contaminated water; 2: Reactant material; 3: Fine cloth filter; 4: Treated sand; 5: Fine cloth filter; 6: Arsenic-free water; 7: Outlet for arsenic-free water; 8: Container for arsenic-free water; 9: Container for treated sand; and 10: Container for reactant material. Table 1. A comparison of the arsenic removal filter systems. Specification System I System II Flow rate 15 L/h 30 L/h Amount of treated sand 1500 g 3000 g Reactant (Steel plant waste) 500 g 1000 g Initial as concentration 1 mg/L 1 mg/L Final as concentration Ͻ3 ␮g/L Ͻ3 ␮g/L Volume of treated water 750 L 1750 L Quality of water for drinking Suitable Suitable Leaching of other metals None None Copyright © 2005 Taylor & Francis Group plc, London, UK 3.2 Laboratory evaluation 3.2.1 Optimization of flow rate Keeping the amount of reactant material and treated sand constant, 500g and 1500g respectively, experiments have been carried out to study the effect of flow rate of arsenic contaminated water (As ϩ3 or As ϩ5 or 1:1 mixture of As ϩ3 and As ϩ5 ) through the filter on the removal efficiency of the filter. The results of these experiments show that irrespective of the arsenic species present in water, effective removal of arsenic can be achieved up to a maximum flow rate of 15 L/h in first system. Arsenic concentration in filtered water increases above prescribed limits as the flow rate exceeds this value. However, it has also been established that if the amount of reactant material and treated sand was raised to 1000g and 3000g, respectively, maximum allowable flow rate that could be achieved is 30 L/h, by changing the dimensions of the filter accordingly as already explained in the experimental section. The results are depicted in Figure 3. 3.2.2 Effect of initial arsenic concentration The effect of initial arsenic (1:1 mixture of As ϩ3 and As ϩ5 ) concentration (varying from 1–4 mg/L) on the arsenic removal efficiency of the filter, in terms of total volume of water filtered (final 276 Figure 2. SEM micrograph of reactant material (ϫ500). Table 2. Characteristics of sand and reactant material. Surface area pH (BET) Adsorbent pH (Water) (As solution) Fe (%) Al (%) Mn (%) Si (%) (m 2 /g) Sand 10.2–10.5 10.2–10.5 8.9–10.5 10.5–11.0 Not detected 79.2–80.0 1 (Yamuna) Sand 8.3–8.5 7.5–8.0 4.7–5.0 11.5–12.0 Not detected 79.8–80.0 4 (Ganga) Reactant 8.5–9.0 8.8–9.0 99.2–99.5 Not detected 0.42–0.45 Trace 0.5 material amount Copyright © 2005 Taylor & Francis Group plc, London, UK arsenic concentration in filtered water Ͻ10 (g/L), using optimized amounts of reactant material and treated sand for the two flow rate systems has been studied and is shown in Fig. 4. As expected, an increase in the arsenic concentration in water leads to a decrease in the total vol- ume of water that can be treated using this filter. 3.2.3 Water quality The filtered water collected in the third chamber has been analyzed for its arsenic concentration, iron (that may leach out from the reactant material during the process) and microbes. The results as enlisted in Table 3 clearly indicate that the quality of the filtered water conforms to the inter- nationally (WHO and US EPA) set drinking water standards (USEPA, 2004). 3.3 Field evaluation After successful laboratory evaluation, seven filters of 15 L/h flow rate were installed in four vil- lages, namely, Kamdevkati, Raghavpur, Simulpur and Chatra villages of 24 Paraganas (N) district of West Bengal, India, to test the viability of this technology in field conditions (Table 4). 277 0 4 8 12 16 20 24 28 051015 20 25 30 35 40 45 50 55 Flow Rate (Lph) Final As conc. (µg/L) WHO / EPA Drinking Water Limit Initial As conc. ~ 1 mg/L Amount of Adsorbent = 500 g Amount of Treated Sand = 1500 g Initial As conc. ~ 1 mg/L Amount of Adsorbent = 1000 g Amount of Treated Sand = 3000 g Figure 3. Optimization of flow rate. 750 1750 625 1455 500 1165 375 875 0 200 400 600 800 1000 1200 1400 1600 1800 Volume of Treated Water (L) 13 Initial As conc. (mg/L) 15 Lph 30 Lph 24 Figure 4. Effect of initial arsenic concentration on treated water volume at the two different flow rates. Copyright © 2005 Taylor & Francis Group plc, London, UK 3.4 Comparison of laboratory and field data A very good concordance was observed between laboratory and field results (Fig. 5) in terms of the capacity of the reactant material used in the filter for the removal of arsenic from the water. The capacity is calculated on the basis of initial arsenic concentration in influent water with respect to the total quantity of water filtered by filter in the laboratory and in field so far. The results as discussed above clearly indicate that the quantity of reactant material used in the filter can be easily and more efficiently used for initial higher concentration of arsenic in water, i.e., up to 4 mg/L and thereafter it remains constant. Therefore, the filter can be successfully used 278 Table 3. Results of water analyses. E.coli (count/100 mL) Type of As conc. (␮g/L) Fe conc. (mg/L) after 48 hrs. As-species Initial After treatment Initial After treatment Initial After treatment As(III) 1000 Ͻ.3 Not detected Ͻ0.3 8 0 As(V) 1050 Ͻ.3 Not detected Ͻ0.3 8 0 Mixture of As (III) and As (V) in the ratio of 1:1 1025 Ͻ.3 Not detected Ͻ0.3 8 0 Table 4. Field evaluation data. Total volume Iron concentration (mg/L) Arsenic concentration (mg/L) Date of of water installation Site of installation filtered 1 Initial Final Initial Final 23/09/03 Kamdevkati Village (Stainless Steel Kit) 10,050 L 0.040 Ϯ 0.001 0.042 Ϯ 0.001 0.068 Ϯ 0.01 0.004 Ϯ 0.001 07/10/03 Chatra Village 1400 L 0.168 Ϯ 0.02 0.063 Ϯ 0.001 0.271 Ϯ 0.02 0.003 Ϯ 0.001 (Plastic Kit) 2 20/11/03 Kamdevkati Village (Stainless Steel Kit) 7260 L 0.105 Ϯ 0.02 0.210 Ϯ 0.02 0.049 Ϯ 0.001 0.003 Ϯ 0.001 20/11/03 Kamdevkati Village (Plastic Kit) 6860 L 0.084 Ϯ 0.001 0.126 Ϯ 0.02 0.135 Ϯ 0.02 Ͻ0.003 Ϯ 0.001 20/11/03 Simulpur Village 6960 L 0.462 Ϯ 0.02 0.168 Ϯ 0.02 0.374 Ϯ 0.02 0.005 Ϯ 0.001 21/11/03 Raghavpur Village (Stainless Steel Kit) 7110 L 0.168 Ϯ 0.02 0.189 Ϯ 0.02 0.180 Ϯ 0.02 Ͻ0.003 Ϯ 0.001 21/11/03 Chatra Village (Plastic Kit) 3 2060 L 0.168 Ϯ 0.02 0.105 Ϯ 0.02 0.271 Ϯ 0.02 0.004 Ϯ 0.001 0 1 2 3 4 04 As conc. (mg/L) As conc. (mg/L) Capacity (mg/g) 0 2 4 6 0 0,4 ba 260,2 Figure 5. Comparison between the capacity of the reactant material used in the filter for the removal of arsenic based on the results obtained from the tests in the laboratory (a) and field evaluation (b). Copyright © 2005 Taylor & Francis Group plc, London, UK up to a maximum initial concentration of 4 mg/L keeping all the experimental conditions same as discussed in experimental section. 3.5 Leaching tests for waste and concrete blocks Leaching tests carried out for the waste generated during the process as well as for concrete blocks as per the standard Toxicity Characteristic Leaching Procedure (TCLP) for solid wastes (EPA protocol SW-846-1311) (www.iwrc.org), gave results that are tabulated in Table 5. 4 CONCLUSIONS The reports collected from the field trials indicate commendable performance of the filters. However, it has been observed that stainless steel filters are more durable than plastic filters for long-term usage and are recommended for further use. The water filter for arsenic removal as discussed above can provide a reliable solution to the basic problem of arsenic contamination in ground water because of its following features: • Requires no energy sources • Easy maintenance • Cost-effective • Environment-friendly • User Friendly • Easy waste disposal ACKNOWLEDGEMENTS Authors wish to express their sincere gratitude to Dr. J.N. Das, Director, NMRL, Ambernath, for granting permission to publish this work. Authors also wish to acknowledge the help provided by Mr. P.K. Singh, NMRL, for carrying out SEM analysis of the samples and Mr. Rajeev Goel, CFEES, Delhi for carrying out arsenic analysis of water samples. Authors would also like to thank Prosun Bhattacharya at the Royal Institute of Technology, Stockholm, Sweden and K:M: Ahmed from the University of Dhaka, Bangladesh for their constructive suggestions on an earlier draft of the manuscript. 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Toxicology Letters 133(1): 113–118. 280 Copyright © 2005 Taylor & Francis Group plc, London, UK . water and quality conform to the drinking water standards for arsenic and iron. 1 INTRODUCTION An alarmingly large population of India and Bangladesh, 66 million in the Gangetic belt of India and 79.9. blocks of M-25 (Singh, 1982) standard grade used in construction industry resulting in no waste generation in the process and making the technology environment-friendly and green. 3 RESULTS AND DISCUSSION 3.1. available, eco-friendly arsenic removal system for the rural people. 273 Natural Arsenic in Groundwater: Occurrence, Remediation and Management – Bundschuh, Bhattacharya and Chandrasekharam