Nutrient amendment for the bioremediation of a chromium-contaminated soil by electrokinetics

This article presents the results of a preliminary laboratory investigation wherein electrokinetics was used for the delivery of nutrients to metal-reducing micro-organ isms in a low permeability clayey soil. In particular, the micro-organisms were used to reduce a toxic and mobile heavy), metal (hexavalent chromium or Cr(VI)) to a less toxic and immobile,form (trivalent chromium or Cr(III)). Three bench-scale electrokinetic experiments were conducted using kaolin as a model low permeability clayey soil, and the kaolin was artificially, contaminated with Cr(VI) at an initial target concentration of 1,000 mg/kg. All the experiments were conducted with a constant electrical voltage gradient of V/cm and included a control test without micro-organisms or nutrients, a test with micro-organisms but without nutrients, and a test with micro-organisms and supplemental nutrients, specifically acetate, phosphate, and ammonium. The results showed that acetate and phosphate amendment by electrokinetics was effective because both nutrients electromigrated into the soil. Moreover, the results indicate that employing the micro-organism cultures improved Cr(VI) reduction. These results suggest that nutrient amendment by electrokinetics for the bioremediation of heavy metals has great potential; however, the microbial strains responsible for Cr(VI) reduction must be identified so the electrokinetic system can be engineered to provide the optimal nutrient, pH, and environmental conditions for these strains.