Mitigation and Remedy of Groundwater Arsenic Menace in India

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Mitigation and Remedy of Groundwater Arsenic Menace in India : A Vision DocumentCoagulation-precipitation process: Aluminum and ferric salts are commonly usedin drinking water treatment, for coagulation of particles and colloids in the water. If theAs content in water is in the range of 0.1 to 1 ppm, under optimized condition of Fedosage and pH, precipitation efficiency and the elimination process may be as high as99%,. With change in Eh / pH ratio efficiency varies appreciably.Lime softening: This treatment is used for reducing hardness of water, and is also aneffective process for As (V) removal. The use of activated charcoal powder increasesthe efficiency as it induces oxidation of As (III). But effectiveness decreases in alkalinecondition.The biggest problem of the above three processes is concerned with the separation ofthe precipitate and disposal of arsenic contaminated coagulated sludge.Ion exchange: It can remove As (V) more efficiently than As (III). In some recentstudies, it has been established that by this process, As5+ level can be reduced to 2 mg/L and the brine regeneration can be done several times without any adverse impact onAs removal. TDS, selenium, sulphate, fluoride and nitrate, present in water, affect thelife of resin adversely. Suspended solid and precipitated iron cause clogging of resinbed. Another disadvantage is that As (III) is hardly removed.Activated alumina: It is a porous oxide with large surface area and it adsorbs As5+under favorable pH condition of 5.5 to 6, but it is also susceptible to various interferingchemicals as in the case of ion exchange process.The great advantage of activated alumina is its simple operation, with regenerationoperation at intervals of one to three months. Unfortunately, activation efficiencydecreases fast. As (III) cannot be removed efficiently. The biggest problem is disposalof highly concentrated sludge with high contents of toxic dissolve solid.Granular ferric hydroxide: It is poorly crystallized B-FeOOH, with very largespecific surface of 250-300 m 2 /g and porosity of 75-80%, which is capable of highadsorption. The grain size ranges from 0.2 to 2 mm. It also acts as fixed bed absorbers,with best efficiency between pH ranges of 5.5 to 9.In addition to As (V), As (III) can also be adsorbed by granular ferric hydroxide. Thepresence of sulphates in raw water has little influence on adsorption capacity. Dependingon As concentrations, the treatment efficiency ranges from 5 to 25g/m 3 of water. Theresidue is solid and the spent absorbent is non-toxic and can withstand temperature of950°C without release of As from the granules. So disposal is less problematic. Phosphate, in raw water, reduces the arsenate adsorption due to interference.NIH & CGWB 113
A Critical Appraisal- Future Risk, Scope to Remediate, Technological Competence, etc.Activated carbon: It may be helpful, to some extent, in removing arsenate, speciallyAs (V) from water, but its efficiency is very low and cost inhibitive.Conventional Fe-Mn removal process: It is effective only in case of raw water,with less concentration of As.Natural oxides: Crushed hematite and feldspar can be used for adsorption of arsenic,in the particle size, range of 200 um; but the maximum capacity is only 2.6 umol/g.There are some other plausible methods of separation of As in laboratory scale.Reverse osmosis and nano-filtration: Efficiency may be as high as 95% in idealsituations, but water rejection is very high, 25-40%, and discharge of large volume ofreject-water, with higher concentrations of As. This may pose a problem.Electro dialysis reversal: Removal efficiency of As (V) crosses 80%, but As (III)can hardly be removed.Table 6.1: Arsenic removal methods and their effectiveness (from Torrens, 1999)Arsenic removal in drinking water: summary of available dataTreatment technology Arsenic in Arsenic out % removal(ppb) (ppb)Chemical precipitationOxidation/iron co-precipitation 110 10-85 23-91Oxidation/iron co-precipitation 200 80-200 0-60Oxidation/iron co-precipitation 1100 99Lime softening 220 30 86Lime softening (pH>10.5) 75 95Lime softening 100 95Oxidation/iron co-precipitation 50 90Oxidation/iron co-precipitation 21 90Oxidation/iron co-precipitation 377 11 95114NIH & CGWB
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ACKNOWLEDGEMENTThe Government of In
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nearly 33 villages in 4 districts i
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(iii) Whether ex-situ removal techn
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6.4 Experiences during Arsenic Remo
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List of FiguresFigure no. Figure ca
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List of TablesTable no. Table Capti
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Mitigation and Remedy of Groundwater Arsenic Menace in India

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