In-situ bioremediation of perchlorate-contaminated soils

Previous research indicates that microbial communities in the rhizosphere are capable of transforming perchlorate to chloride, given an external carbon source such as acetate. Carbon source requirement in perchlorate transformation was independently confirmed in batch slurry experiments conducted with perchlorate-contaminated soils amended with acetate. Rapid degradation of perchlorate after an initial incubation period of about 7 days was observed in acetate-amended soils compared to controls. In subsequent batch studies, perchlorate contaminated soils from the Longhorn Army Ammunition Plant (LHAAP), were treated with organic amendments and liquid carbon sources to determine their ability to stimulate perchlorate biodegradation. The organic amendments tested included poultry and cow manure and cotton waste, and the liquid carbon sources included ethanol, molasses, and methanol. The different amendments stimulated the biodegradation of perchlorate in contaminated soils, with cotton waste resulting in slower rates compared to the other carbon sources. Based on our successful laboratory experiments, pilot tests were initiated at LHAAP. The pilot in-situ bioremediation started in October 2000 consisted of nine 1 x 1m treatment cells, three of which were amended with one of three different carbon sources; poultry manure, cow manure or ethanol. The maximum concentration of perchlorate in the selected treatment plots at the start of the pilot study was 400 mg/kg. Recent site analysis indicates that poultry manure and ethanol addition reduced perchlorate concentrations ranging from 80 to 250 ppm to below detection within 60 and 100 days, respectively, at depths of 24 and 36 inches.