Submitted to: In Situ and on Site Bioremediation Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/6/2005
Publication Date: 1/3/2006
Citation: Hunter, W.J. 2006. Removing selenate from contaminated water with barriers containing soybean oil: laboratory evaluation.. In Situ and on Site Bioremediation Symposium Proceedings. CD-ROM Publication. Interpretive Summary: Selenate is present in surface and groundwaters as a natural constituent and as a contaminant introduced by human activity. Its presence in groundwater is a major agricultural concern in some parts of the country because of its effects on wildlife. Selenate is highly mobile in soils and aquifers and persistent in groundwater. 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 soybean oil which stimulates microbial activity by providing a carbon substrate. This increased microbial activity will reduce selenate and selenite to insoluble selenium (Seo), thus removing the selenium from groundwater. The process was effective. Five of the six columns removed 66 to 70% of the selenate in the supply water by precipitating it as to Seo or by converting it to volatile selenium species. These studies suggest that in situ permeable barrier composed of sand, gravel and small amounts of vegetable oil may be effective at removing selenate and selenite from flowing ground water. Two bacterial species that may be of value in treating selenium contaminated water were isolated from the sand columns.
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 coating sand with soybean oil. The soybean oil provides a carbon substrate that stimulates microbial activity. At the start of the study 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. With two of the columns total amounts of selenate present in the effluent water decreased significantly as did total soluble selenium. Over the 15 week study about 66% of the soluble selenium applied to columns 1 and 2 was removed from the water by the column biobarriers. The addition of 20 mg/L nitrate to the influent water did not interfere with the ability of the columns to remove selenate. Two bacterial isolates were obtained from the column biobarriers. One, A. oryzae, utilized selenate as a term electron acceptor reducing it to elemental selenium. The other, R. radiobacter (syn. A. tumefaciens) reduces selenite to elemental selenium, apparently as a detoxification reaction.