Sewage sludge is a by-product of wastewater treatment plants, which receive a great deal of effluents from industrial, municipal and/or rural sources. According to the national planning, an increase of sewage sludge production will occur in China very soon. So, more attention should be paid to its disposal. Sewage sludge has several characteristics: (1) it contains organic matter; (2) the organic fraction contains humic substances coming from the degradation of organic matter; (3) it contains varying concen...