(562ad) Biological Transformation of Hexavalent Chromium and Carbon Tetrachloride in Aqueous Medium By Shewanella Oneidensis Strain MR1 and Cellulomonas Strain ES6

Hanford Site, operated by the U.S. Department of Energy, which was a nuclear production complex operated between 1943 and 1998, is contaminated with heavy metals, chlorinated organics, inorganics and radioactive wastes. This site poses an environmental risk because of the presence of hexavalent chromium, Cr(VI), introduced as a result of the use of chromate (a corrosion inhibitor) in the reactor cooling water. Chromium migration to the water table can result in a rapid transfer to the Columbia River, which is a main source of drinking water for Native American population in the area and is one of the largest salmon spawning water body in the United States. Therefore, the migration of Cr(VI), which has the Federal drinking water standard of 100 μg/L, could cause severe health risks to both humans and aquatic lives. Currently, the U.S. Government is spending more than $1 billion per year to remediate Hanford Site and to clean up contaminated soil and groundwater, reactors, tanks, chemical processing plants, and ancillary facilities. On the production complex, about 6,300 lbs. of chromium and 38,000 lbs. of carbon tetrachloride have been removed through “Pump and Treat Remediation”. Our overall project is focused on combined chemical/biological degradation of Cr(VI) and chlorinated organics. In this paper, biological degradation of Cr(VI) and CCl₄ will be presented. Shewanella oneidensis strain MR1 and Cellulomonas strain ES6 were used to biologically reduce Cr(VI) to Cr(III). The experiments were conducted using an End-On-End reactor and a mini Incubator Shaker. The batch reactions were conducted under nongrowth anaerobic conditions in the presence of hexavalent chromium and carbon tetrachloride. After 7 days Shewanella oneidensis strain MR1 was able to achieve 82% reduction of Cr(VI) without any competing electron acceptors and 67% reduction in the presence of carbon tetrachloride. On the other hand, Cellulomonas strain ES6 reduced chromium by 43% without any electron acceptor and 35% in the presence of carbon tetrachloride.