CONVERSION OF HEAVY METAL FRACTIONS IN WASTE-ACTIVATED SLUDGE DURING ANAEROBIC DIGESTION

The conversion of chemical fraction with typical heavy metals was investigated, and feasibility for agricultural use of sludge samples was accessed in this work. Anaerobic digestion experiment was conducted on waste-activated sludge from a wastewater treatment plant. Typical heavy metals in sewage sludge were extracted by Tessier step extraction method, and the content of each form as well as total concentration of heavy metals was determined by ICP-OES. The results showed that the heavy metal forms changed obviously during anaerobic digestion, from unstable form to organic matter-bound and residual form, which are relatively stable. Anaerobic digestion can effectively decrease heavy metals mobility and bioavailability of sludge. Sludge after anaerobic digestion can be better for land-use.