BIOLOGICAL TRANSFORMATION OF CR+6 IN SOIL UNDER VARYING REDOX CONDITIONS

The objective of this work was to study the conditions under which hexavalent chromium (Cr+6) in soil at 10°C could be optimally transformed by native soil bacteria to trivalent chromium (Cr+3). Soil contaminated with high and lower concentrations of chromium was collected from a field site. The soil was added to batch vials and electron acceptors (oxygen, nitrate, sulfate), nutrients (N, P), and carbon (brown sugar) were added. Aqueous Cr+6 concentrations were measured over time, and compared to killed controls. In the less contaminated soil, the most rapid Cr+6 removal was noted when carbon and nitrate or sulfate were added. In the highly contaminated soil, carbon addition had a negligible effect. When additional Cr+6 was added to the soil to determine bacterial toxicity, Cr+6 removal rates increased with increasing concentration up to 100 mg/L. The results of this work should help in developing optimal methods to biologically treat chromium contaminated soil.