Submitted to: In Situ and on Site Bioremediation Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 3/15/2003
Publication Date: 7/13/2003
Citation: Hunter, W.J. 2003. Laboratory evaluation of biobarriers containing biodiesel for the in situ remediation of selenate contaminated water. In Situ and on Site Bioremediation Symposium Proceedings. ISBN 1-57477-139-6, Battelle Press, Columbus, OH. Interpretive Summary: Selenate has been detected in surface and groundwaters as a natural constituent and as a contaminant introduced by human activity. It is highly mobile in soils and aquifers and persistent in groundwater. Selenate in groundwater is a major agricultural concern in some parts of the country because of its effects on wildlife. The present study looked at a biological treatment to remove selenate and selenite from groundwater. The approach involves the use of in situ barriers that contain a carbon substrate, biodiesel, that stimulates microbial activity. In theory, the increased microbial activity will remove oxygen from the groundwater. The reducing conditions caused by the increased microbial activity will reduce selenate and selenite to insoluble selenium (Seo), thus removing the selenium from groundwater. The process was only partially effective. Only 15-16% of the selenate/selenite was precipitated to Seo or lost as volatile selenium species. Most, about 85% of the selenium remained as soluble forms in the groundwater. These studies suggest that in situ permeable barrier composed of sand, gravel and small amounts of an insoluble carbon substrate may not be highly effective at removing selenate or selenite from flowing ground water.
Technical Abstract: Selenate has been detected in surface and groundwaters as a natural constituent and as a contaminant introduced by human activity. Laboratory column studies were conducted to see if in situ biobarriers might be used to remove soluble selenate from groundwater by its reduction to insoluble selenium (Seo). The columns contained sand and a biobarrier. For this study the biobarrier was formed by injecting an emulsion containing biodiesel onto the columns. The biodiesel provides a carbon substrate that stimulates microbial activity. After the injection of the biodiesel emulsion, a soil wash was added to provide an inoculum of native microorganisms, and water containing 10 mg/L selenate was pumped through columns. Samples of the effluent water were collected at intervals and analyzed for selenate and selenite. Total amounts of selenate present in the effluent water decreased significantly but total soluble selenium in the column effluents decreased by only about 15-to16%. Increasing the length of the biobarrier failed to decrease the amount of soluble selenium in the effluent water. Biobarriers containing sawdust were also ineffective at removing soluble selenium compounds from flowing water during short-term studies. The results of this study suggest that permeable barriers containing biodiesel or sawdust may not be a very effective process for removing selenate or selenite from contaminated groundwater.