In situ bioprecipitation for remediation of metal-contaminated groundwater

Metal-polluted groundwater co-contaminated by sulfates may be decontaminated by in situ immobilisation based on biological sulfate reduction. This remediation technique is based on the stimulation of sulfate reducing bacteria. Sulfates are reduced to sulfides and heavy metals precipitate as insoluble metal-sulfides. Laboratory tests successfully demonstrated the removal of soluble Zn, Ni, Co and sulfate. Different carbon sources were evaluated as well as the requirements for nutrient addition, pH and redox conditions. A metal-contaminated site was chosen for the pilot-test. Molasses was injected as a carbon source. Monitoring showed a shift of pH and redox conditions followed by a decrease of sulfate and metals concentrations. The results and requirements for in situ metal bioprecipitation are highlighted.