EFFECT OF PH ON METAL SOLUBILIZATION FROM SEWAGE-SLUDGE - A NEURAL-NET-BASED APPROACH

Microbial leaching for heavy metals removal from municipal sewage slud ge is a complex biological process. The ultimate metal solubilization achieved depends on the type of sludge involved (nondigested, aerobica lly digested or anaerobically digested sludge), the decrease in sludge pH as a result of the leaching operation, and the concentration of me tals initially present in the sludge. In addition, the system temperat ure exerts an indirect but strong influence by its effect on the bacte rial growth and acid production process. A neural-net-based model was developed to predict the solubilization of six heavy metals, Cd, Cr, C u, Ni, Pb, and Zn, from sewage sludge using the bioleaching process. T he only input parameters required are the type of sludge, initial meta l concentrations in the sludge, and the sludge pH. The model yielded s atisfactory predictions of metal solubilization when tested with a num ber of actual experimental data.