Bioleaching of Heavy Metals from Civil Sludge by Indigenous Thiobacillus ferrooxidans

The civil sludge taken from Qilidian sewage treatment plant of Guilin was used as the cultivation medium and ferrous sulfate (FeSO₄.7H₂O) was substrate for the growth of bioleaching microorganisms in this research. Through strength environment of bacterial, the indigenous Thiobacillus ferrooxidans(T.f)in fresh sludge was propagated greatly and become the dominant species in this process. Overall the bioleaching procedure included two stages: acidophilus domestication and inoculated cultivation. The first stage research indicated that 10 g/L was the lowest substrate dosage to keep bacterial growing and sludge effective acidification. The second process of bioleaching was conducted in the sequence bath reactor (SBR) with a simplified operation process. The removal rates of high concentration heavy metals of Cu, Zn and Cd could reach 78.3%,77.7% and nearly 99% respectively after 2 days´ running of SBR. The discharge ratio and aeration rate of SBR were controlled to 10/13(30% inoculums volume) and 1.0 L/min.L. Residual contents of the three elements were lower than the limit standard for sludge land application in China.