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

The growth of sulphate reducing bacteria in copper sulphate solutions and their efficacy of removal of copper from those solutions was investigated. The direct role of the bacteria in facilitating copper removal was identified by (i) comparing copper precipitation kinetics in the presence and absence of the bacteria cells and (ii) by observing the morphology and location of the copper precipitates. Copper was removed effectively by SRB to less than 0.1 mg l−1 from sulphate solutions containing 150 mg l−1 or less initial copper concentration. Below 50 mg l−1 initial concentration of copper, little inhibition of sulphate reduction was observed in the five day batch tests. Copper was seen to precipitate out more quickly in the presence of bacteria cells than without bacteria cells, sulphide not limiting. Thus, association of copper with the bacteria cells could promote precipitation rate. Visual observations of the solids indicated dense packing and good settling. Well contrasted images of the unstained bacteria confirmed that the minerals formed were associated with the cell surface. Cells showed a high degree of capsule production in the presence of copper in solution. This phenomena is the most likely reason for the formation of flocculates, fast settling and the dense appearance of the precipitates.