FACTORS AFFECTING TOXIC METALS REMOVAL FROM DIGESTED SEWAGE-SLUDGE BYENRICHED SULFUR-OXIDIZING MICROORGANISMS

Enriched sulphur-oxidizing microorganisms were applied to remove metal s from anaerobically digested sewage sludge in laboratory reactors. Th e pH drop and rise in oxidation-reduction potential (ORP) of the sludg e by microorganisms were mainly responsible for the metal solubilizati on. There was a significant effect of the sulphur amount per unit volu me of sludge, the initial pH of the sludge, the inoculum size and the sludge solids concentration on the pH, the sulphate production rate, t he ORP, the maximum metal solubilization rate, and the time required t o achieve the acceptable level of Cu for sludge land application. The enriched microorganisms were able to grow and reduce the pH at a wide range of initial sludge pH values. Metals (Cu, Zn) were solubilized ef ficiently as a result of decreased pH.