BIOLEACHING OF METALS FROM ANAEROBIC SEWAGE SLUDGE: EFFECTS OF TOTAL SOLIDS, LEACHING MICROORGANISMS, AND ENERGY SOURCE

Abstract

The effects of municipal sewage sludge solids concentration, leaching microorganisms (Thiobacillus thiooxidans or Thiobacillus ferrooxidans) and the addition of energy source (S⁰ or Fe(II)) on the bioleaching of metals from sewage sludge has been investigated under laboratory conditions using shake flasks. The results show that metal solubilization was better accomplished if additional energy source is supplemented to the microorganisms and that T. thiooxidans furnishes, in general, more adequate conditions for the bioleaching than T. ferrooxidans. At a total solids concentration of 70 gL⁻¹ (originally present in the sludge) pH drop and ORP increase are attenuated, so metal solubilization is negatively affected. It was also demonstrated that if lead (Pb) solubilization is to be achieved, than a special combination of microorganism/energy source must be applied.

Keywords:

• Bioleaching
• Thiobacillus
• Sewage sludge
• Metals

ACKNOWLEDGMENT

The authors acknowledge SANASA (Campinas, Brazil), through Dr. R. Rosseto for making available the sewage sludge, Valeria T. Silva for carbon, phosphorus and potassium analysis and Dr. J. C. Rocha (FAPESP 95/05231-0) for the analysis of soluble metals. ATL acknowledges the financial support received from FAPESP (processes: 98/03107-9 and 97/13211-5) and OGJ a research fellowship from CNP_q.