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.. Explanations: 1: Inlet for arsenic contaminated
Trang 1A 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
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-prepre-cipitated 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
Natural Arsenic in Groundwater: Occurrence, Remediation and Management –
Bundschuh, Bhattacharya and Chandrasekharam (eds)
© 2005, Taylor & Francis Group, London, ISBN 04 1536 700 X
Trang 22 MATERIALS 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 As3and As5have been prepared using corresponding salts, NaAsO2and Na2HAsO4 7H2O, respectively Mixture of As3 and As5 (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
Trang 32002, 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 FeAsO4and FeAsO3) and by adsorption onto ferric oxyhydroxide solids The same has been reported by a number of workers earlier also (Su et al 2001)
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.
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 3 g/L 3 g/L Volume of treated water 750 L 1750 L Quality of water for drinking Suitable Suitable
Trang 43.2 Laboratory evaluation
3.2.1 Optimization of flow rate
Keeping the amount of reactant material and treated sand constant, 500 g and 1500 g respectively, experiments have been carried out to study the effect of flow rate of arsenic contaminated water (As3or As5or 1:1 mixture of As3and As5) 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 1000 g and 3000 g, 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 As3and As5) concentration (varying from 1–4 mg/L)
on the arsenic removal efficiency of the filter, in terms of total volume of water filtered (final
Figure 2 SEM micrograph of reactant material (
Table 2 Characteristics of sand and reactant material.
Surface area
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
Trang 5arsenic concentration in filtered water10 (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)
0
4
8
12
16
20
24
28
Flow Rate (Lph)
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
Initial As conc (mg/L)
15 Lph
30 Lph
Figure 4 Effect of initial arsenic concentration on treated water volume at the two different flow rates.
Trang 63.4 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
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
Mixture of As
(III) and As (V) in
Table 4 Field evaluation data.
Total volume Iron concentration (mg/L) Arsenic concentration (mg/L)
installation Site of installation filtered 1 Initial Final Initial Final
23/09/03 Kamdevkati Village
(Stainless Steel Kit) 10,050 L 0.040 0.001 0.042 0.001 0.068 0.01 0.004 0.001 07/10/03 Chatra Village 1400 L 0.168 0.02 0.063 0.001 0.271 0.02 0.003 0.001
(Plastic Kit) 2
20/11/03 Kamdevkati Village
(Stainless Steel Kit) 7260 L 0.105 0.02 0.210 0.02 0.049 0.001 0.003 0.001 20/11/03 Kamdevkati Village
(Plastic Kit) 6860 L 0.084 0.001 0.126 0.02 0.135 0.02 0.003 0.001 20/11/03 Simulpur Village 6960 L 0.462 0.02 0.168 0.02 0.374 0.02 0.005 0.001 21/11/03 Raghavpur Village
(Stainless Steel Kit) 7110 L 0.168 0.02 0.189 0.02 0.180 0.02 0.003 0.001 21/11/03 Chatra Village
(Plastic Kit) 3 2060 L 0.168 0.02 0.105 0.02 0.271 0.02 0.004 0.001
0 1 2 3 4
2 4 6
b a
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).
Trang 7up 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
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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