In order to investigate the elution mechanism of Cu from sewage sludge, both chemical and biological leachings of Cu from CuS were examined by using a batch reactor at pH 2, 3 and 4. The acidification of solution hardly eluted Cu at all pH values. The eluted amount of Cu by ferric sulfate decreased as the pH increased. In the biological leaching by iron oxidizing bacteria, the elution rate of copper at pH 2 and 3 was the fastest. It was found that biological leaching by the addition of ferrous sulfate or ferric sulfate was effective for the elution of Cu at all pHs.
Furthermore, the effect of iron oxidizing bacteria on removal of Cu from anaerobically digested sewage sludge was examined without adding ferrous sulfate. The biological leaching by iron oxidizing bacteria brought about the effective removal of Cu from sewage sludge.