THE COMPOSITION AND CHARACTERISTICS OF ANAEROBICALLY DIGESTED SLUDGE

The composition and characteritics of anaerobically digested sewage sludge. obtainedfrom Jizhuangzi Sewage Treatment Plant in Tianjing. were studied to evalute utilizationpotential of sewage sludge applied to cropland. The results showed that the sewagesludge was rich in organic matter, nitrogen. and phosphrous and that the ratio ofinorganic N to total N was higher in digested sewage sludge than that in undigestedone. Besides, the proportion of NH.+ to NO3 was also much higher in the former thanthat in the latter. Water soluble organic matter. protein, and hemicellulose accounted for57% of total organic matter in the sewage sludge. Concentrations of heavy metals ormetalloid (Cd, Ph, Hg, As. Cr, Ni, Cu, Znj in the sludge were about 2O--40 times higherthan those in the local uncontaminated surface soil. Cd and Zn exhibited higherchemical mobility because they existed mainly in the forms of exchangeable and weaklybound to organic matter.