The indigenous mixed inocula were cultured and enriched from the thickened waste sewage sludge for heavy metal bioleaching. The mixed inocula were then used for bioleaching, and 2 g/L sulphur was added. The influences of FeSO4?7H2O dosage on heavy metals (Zn, Cu, Pb and Cd) and nutrients (nitrogen and phosphorus) bioleaching were investigated. Results show that the addition of FeSO4?7H2O accelerates the bioleaching process. With the FeSO4?7H2O addition, pH of the sludge decreases and the Oxidation Reduction Potential (ORP) increases more rapidly. The presence of FeSO4?7H2O obviously increases the solubilisation of Zn, Cu and Cd, but has insignificant impact on the Pb solubilisation. FeSO4?7H2O also changes the nitrogen loss and the phosphorus loss. The suitable FeSO4?7H2O dosage is 5?10 g/L; higher dosages cannot accelerate the heavy metal bioleaching more. With the addition of 10 g/L FeSO4?7H2O and 2 g/L sulphur powder, 81.4% of Zn, 81.1% of Cu, 67.6% of Pb and 56.6% of Cd are solubilised from the sludge after 15-day bioleaching at 28?C and an agitating speed of 180 r/min.
Keywords: bioleaching, mixed inocula, heavy metals, sewage sludge, nutrients