Reduction of perchlorate and nitrate by salt tolerant bacteria

Spent regenerant brine from ion-exchange technology for the removal of perchlorate and nitrate produces a high salt waste stream, which requires remediation before disposal. Bioremediation is an attractive treatment option. In this study, we enriched for salt tolerant bacteria from sediments from Cargill salt evaporation facility (California, USA), the Salton Sea (California, USA), and a high density hydrocarbon oxidizing bacterial cocktail. The bacterial cocktail enrichment culture reduced ClO4- from 500 to 260 mg 1 in 4 weeks. Salt tolerant bacterial isolates from the enrichment cultures and two denitrifying salt tolerant bacteria, Haloferax denitrificans and Parococcus halodenitricans, substantially reduced perchlorate. The highest rate of perchlorate removal was recorded with the isolate, Citrobacter sp.: 32% reduction in 1 week. This bacterium substantially reduced perchlorate in 0-5% NaCl solutions and maximally at 30 degrees C and at an initial pH 7.5. In simulated brines containing 7.5% total solids, the Citrobacter sp. significantly reduced both perchlorate and nitrate with 34.9 and 15.6% reduction, respectively, in 1 week. Coculture of a potent perchlorate reducing, non-salt tolerant (non-saline) bacterium, perclace and the Citrobacter sp. proved most effective for perchlorate removal in the brine (46.4% in 1 week). This study demonstrates that both anions can be reduced in treatment of brines from ion exchange systems.