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United States Department of Agriculture

Agricultural Research Service

Title: Removing Selenate from Groundwater with Biobarriers Containing Soybean Oil

Author
item Hunter, William

Submitted to: In Situ and on Site Bioremediation Symposium Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: April 29, 2005
Publication Date: June 6, 2005
Citation: Hunter, W.J. 2005. Removing selenate from groundwater with biobarriers containing soybean oil. In Situ and on Site Bioremediation Symposium Proceedings.

Technical Abstract: At high levels selenate is a water contaminant that is toxic to humans and animals. In situ biologically active barriers (biobarriers) might provide a useful approach for removing soluble selenium from water. Laboratory studies were conducted to evaluate the use of biobarriers, formed packing laboratory columns with sand coated with soybean oil, as a method for removing selenate from groundwater. The working hypothesis is that the soybean oil, an energy rich carbon substrate, will stimulate microbial activity and that this increased microbial activity will result in the reduction of selenate to elemental selenium. Elemental selenium is not water soluble and this reduction reaction should remove selenate from the water. For the study a microbial inoculum was added and water containing 10 mg L-1 selenate or 10 mg L-1 selenate plus 20 mg L-1 nitrate was pumped through the sand columns. At intervals the effluent from the columns was collected and assayed for selenate, selenite, nitrate and nitrite. The total amount of selenate present in the effluent water decreased significantly with two of the sand columns that were supplied with selenate alone for 18 weeks. After two weeks operation effluents from these two columns contained no detectable selenate. Transient accumulations of selenite, lasting 5 and 10 weeks, were observed with these columns. In the final weeks of the study neither selenite nor selenate were detected in the effluents of these columns. However, the third column in the study failed to reduce selenate. In the second part of the study three columns were supplied with selenate and nitrate for 24 weeks. Results show that these columns were effective at reducing the amount of both selenate and nitrate present in the influent water. Much of the nitrate in the effluents disappeared within the first week of operation and the amounts of nitrate in the effluents remained low, averaging less than 1 µg ml-1 nitrate-N, for the final 23 weeks of the study. No accumulations of nitrite were observed during the study and the amount of nitrite in the effluents averaged about 0.03 µg ml-1 nitrite-N during the final 23 weeks of the study. The amount of selenate in the effluents declined slowly throughout the study indicating that the columns became increasingly efficient at removing selenate as the study progressed. In the final five weeks of the study the columns were about 95% efficient at removing selenate from the influent water. Only trace amounts of selenite were detected during the study and the average amount of selenite-Se in the effluents was 0.05 µg ml-1. The results suggest that vegetable oil based biobarriers can be used to remove selenate or selenate and nitrate from flowing groundwater.

Last Modified: 10/1/2014
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