Mitigation and Remedy of Groundwater Arsenic Menace in India

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Mitigation and Remedy of Groundwater Arsenic Menace in India : A Vision Documentarsenic-rich mine drainage and the subsequent decrease of arsenic content, down gradient fromwhere discharges crossed limestone outcrops, indicated that limestone is a possible arsenicremoval medium (Davis et al., 1999). Surface area of the limestone is a key parameter,controlling the efficiency of the process. The smaller grain sizes have provided a greater surfacearea per unit weight. Thus, better arsenic removal has been demonstrated.The areas of major concern, regarding feasibility of a limestone-based arsenic removalprocess, are ionic interference, the stability and disposal of arsenic-saturated limestone, and therate at which the process can treat water. Each of these concerns should be addressed. Theprocess should be studied at the molecular level, regarding what compound is formed on orwithin the limestone. A better understanding of the entire process and the composition of thearsenic-rich limestone waste product would likely result from such a study. Perhaps a material,other than limestone, needs to be added to the process to enhance waste product stability. Basedon previous research, iron oxide seems an appropriate choice. Other lime stones should betested. A rock unit can contain various constituents and still qualify for classification aslimestone. One of these minor constituents could greatly enhance the process. Various othernatural waters should be used in upcoming work with a batch reactor. Chemical analyses ofthese natural waters should be done in an attempt to identify as to which ions preferentiallyinterfere. Column experiments, using a constant flow rate, are needed. Understanding the flowmechanics of the process will be essential to the development of a prototype.A prototype cartridge must be designed. Experimental data regarding mass adsorptionratios and necessary residence times, indicating an appropriate cartridge size and flow rate,would assist in the design of a prototype. The intent of any design should be to maximize theefficiency of the limestone-based arsenic removal process, with regard to both limestone massand water volume or flow rate. This assumes the use of 58 smallest feasible limestone grainsizes. Cost and availability factors could affect that assumption. Initial experimental work hasbeen successful in demonstrating the use of limestone to reduce the arsenic concentrations of aprepared standard solution. Prototype design and arsenic-rich limestone disposal must be addressed,before the ultimate feasibility of applying limestone-based arsenic removal systems,can be determined. Further work should focus on expanding the applications of the process,namely, to include removing arsenic from natural waters as well as standard solutions.6.3.3 Remediation of Arsenic contaminated Soils by in situ Chemical FixationSubsurface soils, from several industrial facilities, are contaminated with arsenicbecause of the application of arsenic containing herbicide. Low cost in situ chemical fixationtreatment is designed to react with contaminated soils directly, against the treatment solutions tocause the formation of insoluble arsenic-bearing phases, and thereby, decreases theenvironmental leachability of arsenic (Xang, Li et al). Combinations of ferrous sulfate, potassiumpermanganate and calcium carbonate are used as major reagents for the chemical fixationNIH & CGWB 117
A Critical Appraisal- Future Risk, Scope to Remediate, Technological Competence, etc.solutions. Sequential leaching, with an extraction fluid described in the EPA syntheticprecipitation leaching procedure (SPLP), has been used to simulate the long-term leachingbehavior of treated soils under natural conditions. The results indicate that the fixation solution,with only ferrous sulfate, have the best effect among all the reagent combinations, reducingSPLP-leachable arsenic by as much as 90%.A modified 4-step sequential extraction procedure can be used to further study thechemical fractionation of soil As, before and after chemical treatment. Sequential extractiondata would likely show that the soil treatment has greatly reduced the most readily labile portionof arsenic which is extracted in the 1st step of the sequential extraction, with its value lowered toless than one tenth than that of untreated soil. The potentially mobile fraction of soil arsenic,extracted in the 2nd step of the sequential extraction, is also considerably smaller. It is shownthat after treatment; most of the As in the soil is transferred to amorphous Fe oxyhydroxideswhich are the major phases extracted in the 3rd step. X-ray absorption near edge spectra showAs is present as As (V) in the treated soil. Extended X-ray absorption fine structure (EXAFS)spectral analysis indicates that a large portion of the total soil arsenic is co-precipitated andincorporated into newly formed amorphous Fe oxides after treatment.6.4 Experiences during Arsenic Removal Technology Evaluation in Technology ParkSchool of Fundamental Research has been entrusted to conceptualize, execute andmanage the evaluation programme of Arsenic Removal Technologies, using an ArsenicTechnology Park during August 2001 to September 2003. It has gained some knowledge aboutthe problems and genesis of arsenic mitigation in dynamic field conditions. Some of which arementioned below.(i)Tube-well: The probable scenario has been in operation for more than a decade, withmost of the tube-wells, which have been selected, based on their contamination level,and has practically concluded their critical life span. These have been found to be thesame in all cases. Re-sinking of all the tube wells, due to sudden heavy drawl of water,becomes a necessity.Since most of the lift pumps are used to pump water for gravitational drawdown throughthe media column natural system, resistance seems to affect the performance of thetube wells, which are otherwise meant for free lifting of water without any resistance inthe path. Thus, difference in pull-push process interaction within the tube well generatesa resultant back-pressure. Continuous over use disturbs the performance of the liftpumps as well as creates an impact on the interface mechanism. It is one of the criticalissues that seem to affect the overall performance of ARPs.118NIH & 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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