Influence of ferrous ions on extracellular polymeric substances content and sludge dewaterability during bioleaching

Pretreatment of activated sludge with sulfuric acid and bioleaching using Acidithiobacillus ferrooxidans along with addition of Fe2+ on sludge dewaterability was investigated. The sludge dewatering efficiency in terms of capillary suction time (CST) and specific resistant to filtration (SRF) was increased with a decrease in sludge pH. A pH of 2.67 was found to be optimum for dewatering, at which 81% and 63% reduction of CST and SRF were achieved, respectively. The dewaterability of sludge was enhanced after the addition of Fe2+ and A. ferrooxidans. Ideal concentration of Fe2+ was 2 g/L for sludge dewaterability, which showed 96% and 88% reduction in CST and SRF, respectively. In the control sludge, maximum part of the biopolymeric macromolecules was contributing by the tightly bound extracellular polymeric substances (TB-EPS). At optimum Fe2+ concentration, total EPS was reduced by 73%, enhancing sludge dewaterability. Bioleaching conducted by A. ferrooxidans could solubilized 88% Cu and 99% Zn within 120 h.