Mitigation and Remedy of Groundwater Arsenic Menace in India

More documents

Recommendations

Info

Mitigation and Remedy of Groundwater Arsenic Menace in India : A Vision DocumentAn adequate nutrient supply should be available to the microbes to enhance andstimulate growth. If the initial solution is nutrient deficient, nutrient addition may be necessary.Iron or hydrogen sulfide may also be added. For biologically enhanced iron precipitation, ironmust be present in the water to be treated. The optimal iron level depends primarily on thearsenic concentration.Biological treatment for arsenic is used primarily to treat water above-ground inprocesses that use microorganisms to enhance precipitation/co precipitation. This technologymay require pretreatment or addition of nutrients and other treatment agents to encourage thegrowth of key microorganisms. The leachate from bioleaching requires additional treatment forarsenic prior to disposal.Another process uses anaerobic sulfate-reducing bacteria and other direct arsenicreducingbacteria to precipitate arsenic from solution as insoluble arsenic sulfide complexes. Thewater containing arsenic is typically pumped through a packed-bed column reactor, whereprecipitates accumulate until the column becomes saturated. The arsenic is then stripped and thecolumn is biologically regenerated. Hydrogen sulfide has also been used in suspended reactors tobiologically precipitate arsenic out of solution. These reactors require conventional solid/liquidseparation techniques for removing precipitates. Removal of arsenic from soil biologically via"accelerated bioleaching" has also been tested on a bench scale. The microbes in this systemproduce nitric, sulfuric and organic acids which are intended to mobilize and remove arsenicfrom ores and sediments. This biological activity also produces surfactants, which can enhancemetal leaching.5.3.4 Electrokinetic TreatmentElectrokinetic treatment is an emerging remediation technology designed to removeheavy metal contaminants from soil and ground water. It is an in-situ treatment technology andtherefore does not require excavation of contaminated soil or pumping of contaminated groundwater. Fine-grained soils are more amenable to electrokinetic treatment due to their largesurface area, which provides numerous sites for reactions necessary for electrokineticprocesses (Acar and Gale, 1995; Evanko and Dzomback, 1997). However, its effectivenessmay be limited by a variety of contaminants and soil and water characteristics. In addition, itstreatment depth is limited by the depth to which the electrodes can be placed. The technologyhas limited number of applications for arsenic.Electrokinetic remediation is based on the theory that a low density current will mobilizecontaminants in the form of charged species. A current passed between electrodes is intended tocause water, ions and particulates to move through the soil, waste and water (Will, 1995).Contaminants arriving at the electrodes can be removed by means of electroplating orelectrodeposition, precipitation or coprecipitation, adsorption, complexing with ion exchangeresins, or by pumping of water (or other fluid) near the electrode.NIH & CGWB 97
Technological Options and Arsenic Removal TechnologiesThe chemicals used in electrokinetic process for arsenic removal include sulfuric acid,phosphoric acid and oxalic acid. In situ electrokinetic treatment of arsenic uses the naturalconductivity of the soil (created by pore water and dissolved salts) to affect movement of water,ions and particulates through the soil (Will, 1995). Water and/or chemical solutions can also beadded to enhance the recovery of metals by electrokinetics. Positively charged metal ormetalloid cations, such as As (V) and As (III) migrate to the negatively-charged electrode(cathode), while metal or metalloid anions migrate to the positively charged electrode (anode)(Evanko and Dzomback, 1997). Extraction may occur at the electrodes or in an external fluidcycling/extraction system. Alternately, the metals can be stabilized in situ by injecting stabilizingagents that react with and immobilize the contaminants. Arsenic has been removed from soilstreated by electrokinetics using an external fluid cycling/extraction system.This technology can also be applied ex-situ to groundwater by passing the waterbetween electrodes. The current causes arsenic to migrate toward the electrodes, and alsoalters the pH and oxidation-reduction potential of the water, causing arsenic to precipitate/coprecipitate. The solids are then removed from the water using clarification and filtration (Pensaert,1998).A pilot-scale test of electrokinetic remediation of arsenic in ground water wasconducted in Belgium in 1997. This ex situ application involved pumping groundwatercontaminated with zinc, arsenic and cadmium and treating it in an electrokinetic remediationsystem with a capacity of 6,600 gpm. The treatment system precipitated the contaminants andthe precipitated solids were removed using clarification and filtration. The electrokinetictreatment system did not use additives or chemicals. The treatment reduced arsenicconcentrations in groundwater from 0.6 mg/L to 0.013 mg/L. The reported costs of thetreatment were $0.004 per gallon for total cost, and $0.002 per gallon for O&M (Pensaert,1998).5.4 Waste Disposal / Sludge ManagementWaste disposal is an important consideration in the treatment selection process. Arsenicremoval technologies produce several different types of waste, including sludges, brine streams,backwash slurries and spent media. These wastes have the potential for being classified ashazardous and can pose disposal problems.The arsenic-rich sludge should be disposed in a controlled manner. According to thestudy conducted by AIIH&PH, arsenic rich sludge may be disposed by the following method:• Disposal in on-site sanitation pits,• Mixing with concrete in a controlled ratio,• Mixing with clay for burning for brick manufacturing.98NIH & CGWB
Page 5:
ACKNOWLEDGEMENTThe Government of In
Page 8 and 9:
nearly 33 villages in 4 districts i
Page 10:
(iii) Whether ex-situ removal techn
Page 14 and 15:
6.4 Experiences during Arsenic Remo
Page 16 and 17:
List of FiguresFigure no. Figure ca
Page 18 and 19:
List of TablesTable no. Table Capti
Page 20 and 21:
Mitigation and Remedy of Groundwate
Page 22 and 23:
Page 24 and 25:
Page 26 and 27:
Page 28 and 29:
Page 30 and 31:
Page 32 and 33:
Page 34 and 35:
Page 36 and 37:
Page 38 and 39:
Page 40 and 41:
Page 42 and 43:
Page 44 and 45:
Page 46 and 47:
Page 48 and 49:
Page 50 and 51:
Page 52 and 53:
Page 54 and 55:
Page 56 and 57:
Page 58 and 59:
Page 60 and 61:
Page 62 and 63:
Page 64 and 65:
Page 66 and 67: Mitigation and Remedy of Groundwate
Page 102 and 103: 5.2.2 Co-precipitationMitigation an
Page 124 and 125: 5.8 SummaryMitigation and Remedy of
Page 166 and 167:
Page 168 and 169:
Page 170 and 171:
Page 172 and 173:
Page 174 and 175:
Page 176 and 177:
Page 178 and 179:
Page 180 and 181:
Page 182 and 183:
Page 184 and 185:
Page 186 and 187:
Page 188 and 189:
Page 190 and 191:
Page 192 and 193:
Page 194 and 195:
Page 196 and 197:
Page 198 and 199:
Page 200 and 201:
Page 202 and 203:
show all

Mitigation and Remedy of Groundwater Arsenic Menace in India

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?