Comparison of Ethanol and H2 for Stimulating Denitrification and U Reduction in Sediment Columns

One of the more promising strategies for the in-situ remediation of uranium-contaminated groundwater involves “biostimulation” of dissimilatory metal-reducing bacteria (DMRB). Previous researchers have used ethanol as an electron donor substrate to promote microbial denitrification and uranium reduction. However, the high nitrate concentrations resulted in excessive microbial growth and associated aquifer bioclogging. The purpose of this research project is to evaluate the feasibility of using membrane-delivered hydrogen as an alternative electron donor to stimulate microbial denitrification in the acidic uranium-contaminated sediments from Oak Ridge National Lab (ORNL). This research uses three parallel columns that have been packed with contaminated ORNL aquifer sediments and continuously fed with uranium- and nitrate-contaminated groundwater. Two columns are supplied with hydrogen and ethanol, respectively, and the third is supplied with no exogenous electron donor substrate as a negative control. Throughout the experiment inorganic anions are being analyzed. The results indicate that both hydrogen and ethanol are effective electron donor substrates for stimulating denitrification in the ORNL sediments. Significant nitrate removal has been achieved in both the hydrogen- and ethanol-fed columns, whereas negligible denitrification has been observed in the control column. Nitrate reduction in the hydrogen-fed column was occurred more rapidly than in the ethanol-fed column. Greater than 88% nitrate reduction has been consistently achieved in both columns. Finally, higher nitrite production has been observed in the hydrogen-fed column than in the ethanol-fed column. Ongoing studies are comparing the effectiveness of ethanol and hydrogen as electron donor substrates for stimulating microbial reduction and immobilization of uranium and molybdenum in groundwater.