Evaluation of bioleaching process for the simultaneous reduction of metals and total coliform from sewage sludge

Bioleaching has been proven to be a promising technology for removing heavy metals from the sewage sludge over many years. The main objective of this research is to evaluate the bioleaching process for the simultaneous reduction of three heavy metals - copper(Cu), cadmium(Cd), zinc(Zn) and total coliform from the sewage sludge of the Ashbridges Bay Treatment Plant (ABTP). Bioleaching was carried out with adapted activated sludge containing high concentration of iron oxidizing bacteria T. ferrooxidans using ferrous sulphate as a substrate without adjusting the sludge initial pH to about 4 with acid. The results demonstreated that simultaneous metal removal efficiencies of Cu, Zn were 70% and 74% for Cd respectively after 10 days of bioleaching. The final pH and ORP were found 2.44 and 533 respectively. After this research, it was also observed that the process of bioleaching by T. ferrooxidans is very efficient for the reduction of total coliform from the sludge. This proces allows a considerable reduction in total coliform (3-4 log removal) for the activated sludge examined over a 10 day period.