The role of sulfate reducing bacteria in copper removal from aqueous sulfate solutions

Grown waters contaminated with copper from the mining industry are matters of concern in Canada. This research investigated the feasibility of using sulfate-reducing bacteria (SRB) for treatment of copper sulfate solutions. The growth of sulfate reducing bacteria in copper sulfate solutions and their efficiency of removal of copper from those solutions were investigated by (i) varying the copper concentration from 0-200 ppm, (ii) comparing copper precipitation between SRB enriched from a mixed culture and two pure cultures: Desulfovibrio desulfuricans, and Desulfovibrio vulgaris, and (iii) the study of copper removal kinetics. Electron microscopy and subsequent image analysis of the micrographs detennined the location of copper precipitates and idicated the direct role of the bacteria in copper removal. Copper was removed effectively by the SRB enrichments to less than 0.1 ppm from copper-sulfate solutions containing 150 ppm or less initial copper concentration. All cultures having copper included showed some degree of sulfate inhibition after five days of incubation, although this inhibition was not very significant below 100 ppm initial copper concentration. Kinetic experiments indicated that precipitates of copper form very early in the incubation period. This early precipitation is most likely due to the reaction of copper ions with hydrogen sulfide present in the inocula. Desulfovibrio desulfuricans, and Desulfovibrio vulgaris removed copper from sulfate solution, but not as effectively as the SRB enrichments. Above 50-ppm initial concentration of copper, significant inhibition of sulfate reduction was observed. Visual observations of the precipitates and solids indicated dense packing and good settling. Well-contrasted images of unstained bacteria confirmed that copper sulfides formed when associated with the cell surface. Cells showed a high degree of capsule production in the presence of copper in solution. This phenomenon is the most likely reason for the formation of the flocculates.Applied Science, Faculty ofChemical and Biological Engineering, Department ofGraduat