A NOVEL TECHNIQUE FOR ARSENIC REMEDIATION WITH FE-MN OXIDE PRECIPITATION IN AN ARTIFICIAL AQUIFER: PRELIMINARY RESULTS

High arsenic concentrations (50 to 180 µg/l) occur in groundwater in Badkulla, a small village situated in the Nadia district in West Bengal, India. Groundwater supplied by the Public Health Engineering Department, or directly withdrawn from municipal and household wells does not undergo arsenic removal. This poses a potential threat to the local people drinking the contaminated groundwater.

We have set up a pilot plant to treat the As-rich groundwater based on in situ precipitation of Fe-Mn oxides in an artificial aquifer. It is hypothesized that As will actively precipitate with the Fe-Mn oxides. The artificial aquifer (21 m x 21 m x 6 m) was dug and filled with coarse river sand. The aquifer was lined on top and bottom by an impermeable rubber liner. The raw water is sterilized by passing through an UV-unit before it is injected into the artificial aquifer. We also injected Fe-oxidizing microorganisms into the aquifer to accelerate the precipitation process. Submersible pumps continuously pump in and out groundwater through the aquifer after passing via an aeration tank. Potentially 200 m3 of groundwater can be treated every day if the plant works at full-capacity. Preliminary results indicate that over the last two months (since the pilot plant began running in May), we see substantial change in the groundwater chemistry of untreated versus treated water, which is very promising. The results are indicated below – the treated water is indicated within parenthesis: pH: 7.0 (7.0); suspended solids (mg/l): 6.13 (2.25); Total Fe (mg/l): 1.89 (0.08); Fe2+ (µg/l): 146 (11); As (µg/l): 53 (below detection limit); NO3 (mg/l): 0.10 (0.10); SO4 (mg/l): 0.75 (0.25). Another added advantage is that limited human intervention or maintenance is involved in the whole procedure. While initial investments are slightly high, we believe that long-term benefits would outweigh the options of installing more of these remediation plants in the As affected areas.