The possibility of using indigenous iron-oxidizing bacteria for biological leaching was studied to remove heavy metals from sewage sludge economically. It was confirmed that the indigenous iron-oxidizing bacteria existed in anaerobically digested sewage sludge. The oxidation activities of ferrous iron of the indigenousiron-oxidizing bacteria and the pure species, Thiobacillus ferrooxidans, were nearly equal.
Biological leaching of heavy metals from metal sulfides such as CuS, CdS and ZnS and anaerobically digested sewage sludge was investigated at pH 3 using indigenous iron-oxidizing bacteria. The results showed that the inoculation of the bacteria accelerated the elution rate of Cu from copper sulfide and sewage sludge. It was concluded that the indigenous iron-oxidizing bacteria existing in sewage sludge has an important role to remove heavy metals from the sludge effectively.