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item Hunter, William

Submitted to: Current Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/17/2006
Publication Date: 9/1/2006
Citation: Hunter, W.J. 2006. Removing selenate from water with a vegetable oil based biobarrier. Current Microbiology. Vol. 53: 244-248.

Interpretive Summary: Selenate is present in both ground- and surface waters as a natural constituent and as a contaminant introduced by human activity. Its presence in groundwater is a concern because of its potential effect on human and animal health. Selenate is highly mobile in soils and aquifers and persistent in groundwater. The present study looked at an in situ biological treatment that might be used to remove selenate from groundwater. The approach involves the use of in situ barriers that contain soybean oil. The oil stimulates microbial activity by providing a carbon substrate and the increased microbial activity reduces selenate to insoluble selenium (Seo), thus removing the selenium from groundwater. The process was effective. Five of the six columns removed the selenate in the supply water by precipitating it as to Seo. These studies suggest that an in situ permeable barrier composed of sand, gravel and small amounts of vegetable oil would be effective at removing selenate from flowing groundwater.

Technical Abstract: Vegetable oil based permeable reactive biobarriers (PRBs) were evaluated as a method for remediating groundwater containing unacceptable amounts of selenate. PRBs formed by packing laboratory columns with sand coated with soybean oil were used. In an initial 24-week study a simulated groundwater containing 10 mg L-1 selenate-Se was supplied to three soil columns and the selenate and selenite content of the effluent waters monitored. Two of the soil columns were effective at removing selenate and, during the final 21 weeks of the study, effluents from these columns contained almost no selenate or selenite. Almost all (95%) of the selenate removed was recovered as immobilized selenium sequestered in the solid matrix of the column. For unknown reasons the third column failed to reduce selenate. A second study looked at the ability of PRBs to remove selenate when nitrate was present. Three columns evaluated but the water supplied to these columns contained 20 mg L-1 nitrate-N and 10 mg L-1 selenate-Se. Nitrate quickly disappeared from the effluents of these columns and during the final 23 weeks of the study the nitrate content of the effluent water averaged less than 0.03 µg ml-1 nitrate-N. Selenate was also removed by these columns but at a slower rate than observed with nitrate. In the final six weeks of the study about 95% of the selenate applied to the columns was removed. In situ PRBs containing soybean oil might be used to remediate groundwater contaminated with both selenate and nitrate.