| Municipal sludge not only contains abundant N, P, K and organic matter, but also consists of various deleterious substance including heavy metals, organic pollutants and pathogenic bacterium and so on. Nowadays, the municipal wastewater treatment rate in China will rapidly increase which indicate a dramatic increase in sewage sludge production in China very soon. How to disposal sewage sludge will be a complex and difficult environmental problem. In this paper, the physiochemical properties of sewage sludge from different wastewater treatment plants (WWTP) in China were investigated, and the environmental risks of different ways for sewage sludge disposal were also discussed. The maior results were summarized as follows:(1) Silt fraction and sand fraction were main substance in sewage sludge. Clay fraction was often below 10%.No gravel fraction was found in sewage sludge.(2) Quartz and calcite were main mineral in sewage sludge. Some sewage sludges also had felspar, maghemite and clay mineral including illite, kaolinite, chlorite, and muscovite etc.(3) The high heating value of sewage sludge ranged from 4232.75—19466.26J/g. The ignition temperature and organic matter were the important factors to influence the low heating value of sewage sludge. When the ignition temperature was low, and the content of organic matter was high, the low heating value would high.(4) Zn was the most primary heavy metal pollutant in sewage sludges, the mean content of Zn reached 1179.74mg/kg. The concentration of Cu, Cr, Pb and Ni was relatively high while the concentration of high toxic metals like As and Cd was low in sewage sludge. The content of heavy metals in Pharmacy sewage sludges were low. But the content of Cu and Zn in galvanization sewage sludge and Cr in tannery sewage sludge were extraordinary high.As, Cr, Cu and Pb in sewage sludge were primarily distributed in oxidable and residual phase. Cd was primarily existed in residual phase.The majority of Ni and Zn were associated with soluble and reducible phase. EDTA solution could extract effectively the heavy metals in sewage sludge. The best efficiency and economic concentration for extracting heavy metals in sewage sludge was 0.06M/L..(5) The total contents of 15 PAHs, categorized as priority pollutants by US EPA, rang from2.511—23.270 mg/kg. The content ofΣPAHs in industry sewage sludge was slightly higher than domestic sewage sludge. Individual PAH content varied dramatically in different sewage sludges. The content of pyrene, ranged form 0.179—10.247mg/kg, was the highest PAH in almost all sewage sludges, the combustion processes and the release of petroleum are both the main sources for PAHs. The summation of the content of two rings and three rings PAHs showed positive correlation with the content of Cd, but showed negative correlations with the content of Ni. The heavy metals may affect the activity of microbe, and by this way to influence the degradation of PAHs in sewage sludge.(8) The Compressive strength, radioactivity and heavy metal leaching ability of brick manufactured by using of sludge as an addition material were investigated. Results of tests indicated that the compressive strength reach the Chinese National Standards of top grade brick, and the radioactivity of the brick also measure up the criteria of Chinese National Standards (GB6566-2000) . The toxic characteristic leaching tests of brick also showed that the metal leaching level was low which indicated that the heavy metals were immobilized when sewage sludge made in bricks.(9) Benzene series would release when sewage sludge was anhydrated. The concentrations of benzene series released from sewage sludge increased when the heat temperature increased. The percentage of water in sewage sludge was another factor which influence the release of benzene series. The percentage of water should not be vaporized too much, otherwise, a great deal of benzene series would release from sewage sludge.(10) Most sewage sludges were observed to be inhibitory to the germination of seeds, but some had the function of promoting the germination of seeds. Sludge organic matter had much more phytotoxic to seed germination than inorganic matter.
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