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United States Department of Agriculture

Agricultural Research Service

Title: Removing Selenite from Groundwater with An in Situ Biobarrier: Laboratory Studies

Authors
item Hunter, William
item Kuykendall, Larry

Submitted to: Current Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 6, 2004
Publication Date: March 23, 2005
Citation: Hunter, W.J., Kuykendall, L.D. 2005. Removing selenite from groundwater with an in situ biobarrier: laboratory studies. Current Microbiology. 50:145-150.

Interpretive Summary: Biobarriers are a promising new in situ technology for removing a number of groundwater contaminants from water. Biobarriers are placed in the aquifer below or downstream of the contaminant plume and the contaminant is removed as the groundwater flow carries it through the barrier. Such barriers may be created by digging a trench and backfilling the trench with a mixture of sand, gravel and carbon substrate or by injection of a substrate into the aquifer. Microbial activity in deeper soils and aquifers is usually limited by the availability of carbon. The present study evaluated the removal of a heavy metal, selenite, from water by a vegetable oil based laboratory biobarrier. The study showed that the vegetable oil in the biobarrier serves as the carbon substrate stimulating microbial activity. The microbial activity in the biobarriers resulted in the chemical reduction of the selenite to elemental selenium. While selenite is highly soluble in water selenium is insoluble and precipitates out of the water within the biobarrier. This process greatly decreases the amount of selenite in the groundwater.

Technical Abstract: Selenite is present in surface and groundwaters as both a natural constituent and as a water contaminant introduced by human activity. It is often present at levels that are toxic to both humans and animals. In situ biologically active barriers (biobarriers) might be useful as a method for removing selenite from water. Laboratory biobarriers, formed on laboratory columns by packing the columns with sand coated with soybean oil, were used as models of in situ biobarriers to see if these barriers might reduce soluble selenite to insoluble selenium (Seo). In soil, below the root zone, the activity of microorganisms is usually limited by substrate availability and soybean oil provides a carbon substrate that stimulates microbial activity. Water containing 20 mg L-1 nitrate-N and 10 mg L-1 selenite-Se was pumped through the columns for 74 days. Samples of the effluent water were analyzed for nitrate and selenite at intervals. The nitrate content of the effluent waters dropped to 1 mg L-1 N within a few days and remained low, averaging 0.10 ± 0.03 mg L-1 N for the rest of the study. The amount of selenite present in the effluent remained high for the first two weeks of the study but then slowly declined. From day 28 until the end of the study the amount of selenite-Se in the column effluents averaged 0.20 ± 0.04 mg L-1, a decrease of 98%. At the end of the study about half of the selenite-Se applied to the columns was recovered as immobilized selenium trapped by the biobarrier. The results of this study suggest that permeable barriers containing vegetable oil might be used as a process for removing selenite from contaminated groundwater.

Last Modified: 12/18/2014
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