In-Situ Bioremediation of Perchlorate in Groundwater and Soil
Historical, uncontrolled disposal practices have made perchlorate a significant threat to drinking water supplies in the United States. In-situ bioremediation (ISB) technologies are cost effective and provide an environmental friendly solution for treating contaminated groundwater and soil.
In situ bioremediation was considered as an option for treatment of perchlorate in groundwater and soil in Lockheed Martin Corporation's Beaumont Site 2 (Beaumont, CA). Based on the perchlorate distribution and concentration in the ground, in-situ remediation within the site was divided into three parts (groundwater plume, source area groundwater remediation and vadose zone soil remediation). In both groundwater remediation studies, biological reduction of perchlorate was readily achieved within one week by amending electron donating substrates. In both column studies, perchlorate reductions were observed within two weeks operation and emulsified oil substrate (EOS) had the best performance as electron donor in terms of effectiveness and longevity in both column studies. In the vadose zone remediation study, perchlorate degradation did not occur in 20% moisture content microcosms. However, perchlorate reduction occurred under saturated conditions with the same soil and both EOS and glycerin as electron donors.
To investigate the impact of soil moisture condition on perchlorate remediation, soil microcosm studies were conducted with different soils under different mass water contents. Optimum soil moisture content for perchlorate bioremediation varied significantly in different soils. Anaerobic respiration processes other than denitrification were all limited by unsaturated moisture condition in the soil. Dominant electron acceptor in the unsaturated microcosms was oxygen. However, eliminating oxygen in the soil system using an anaerobic chamber did not result in perchlorate reduction. Addition of humic acid as an electron shuttling mediate reduced soil redox potential significantly but was not able to promote perchlorate reduction under unsaturated condition.
In-situ bioremediation of perchlorate was readily achieved in groundwater but it was more challenging in vadose zone. Soil moisture was identified as a key factor in perchlorate remediation and optimum moisture condition in different soil had large variation. The results from this research provide basis for designing and optimization of in-situ bioremediation of perchlorate in different soils and groundwater.