Improvement of sludge dewaterability and removal of sludge-borne metals by bioleaching at optimum pH

► Co-addition of Fe2+ and S0 as energy substances accelerate bioleaching process. ► Best initial concentrations of Fe2+ and S0 are 2 g/L and 2 g/L. ► pH ∼ 2.4 is the optimum end point for sludge dewatering in sludge bioleaching. ► 85% and 40% of sludge-borne Cu and Cr could be removed at pH ∼ 2.4.