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Exploring sand and bentonite - enhanced sand as filter media for nitrate removal

Malini, R and Sudhakar, MR (2014) Exploring sand and bentonite - enhanced sand as filter media for nitrate removal. In: 5th International Slow Sand and Alternative Biological Filtration Conference, JUN, 2014, Nagoya, JAPAN, pp. 525-532.

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Abstract

Increasing nitrate concentrations in ground water is deleterious to human health as ingestion of such water can cause methemoglobinemia in infants and even cancer in adults (desirable limit for nitrate as NO3 - 45 mg/L, IS code 10500-1991). Excess nitrate concentrations in ground water is contributed by reason being disposal of sewage and excessive use of fertilizers. Though numerous technologies such as reverse osmosis, ion exchange, electro-dialysis, permeable reactive barriers using zerovalent iron etc exists, nitrate removal continues to be one of challenging issue as nitrate ion is highly mobile within the soil strata. The tapping the denitrification potential of soil denitrifiers which are inherently available in the soil matrix is the most sustainable approach to mitigate accumulation of nitrate in ground water. The insitu denitrification of sand and bentonite enhanced sand (bentonite content = 5%) in presence of easily assimilable organic carbon such as ethanol was studied. Batch studies showed that nitrate reduction by sand follows first order kinetics with a rate constant 5.3x10(-2) hr(-1) and rate constant 4.3 x 10(-2) hr(-1) was obtained for bentonite-enhanced sand (BS) at 25 degrees C. Filter columns (height = 5 cm and diameter = 8.2 cm) were constructed using sand and bentonite-enhanced sand as filter media. The filtration rate through both the filter columns was maintained at average value of 2.60 cm/h. The nitrate removal rates through both the filter media was assessed for solution containing 22.6 mg NO3-N/L concentrations while keeping C/N mass ratio as 3. For sand filter column, the nitrate removal efficiency reached the average value of 97.6% after passing 50 pore volumes of the nitrate solution. For bentonite-enhanced sand filter column, the average nitrate removal efficiency was 83.5%. The time required for effective operation for sand filter bed was 100 hours, while bentonite-enhanced sand filter bed did not require any maturation period as that of sand filter bed for effective performance because the presence of micropores in bentonite increases the hydraulic retention time of the solution inside the filter bed.

Item Type: Conference Proceedings
Additional Information: Copyright for this article belongs to the IWA PUBLISHING, ALLIANCE HOUSE, 12 CAXTON ST, LONDON SW1H 0QS, ENGLAND
Keywords: Biodenitrification; Bentonite; Slow sand filtration; Drinking water
Department/Centre: Division of Mechanical Sciences > Centre for Sustainable Technologies (formerly ASTRA)
Depositing User: Id for Latest eprints
Date Deposited: 14 Feb 2015 13:32
Last Modified: 14 Feb 2015 13:32
URI: http://eprints.iisc.ac.in/id/eprint/50793

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