Environment Risk Study For The Drying-incineration Process Of Sludge

In recent years, the disposal of solid waste has become a bigger issue in China. As an important part of solid waste, the sludge has complex composition so it is difficult to treat and is possible to bring about secondary pollution. The sludge dying and incineration system is a good approach to reuse sludge heat and is adopted and promoted in some big and medium cities. But environmental risk study is in the primary process and lack of systematic assessment.Based on investigation of sludge drying and incineration process, the environmental risk elements were identified from drying and incineration respectively. For sludge drying unit, the odor emission was studied and the internal and external reasons of dust fire/explosion during sludge dying were analyzed by using preliminary hazard analysis (PHA) on the basis of theory of accident causation. The heavy metals and dioxin emission from incineration was discussed and results indicated that heavy metals mainly exist in residues and fly ash. Dioxin emission concentration in flue gas can generally meet the standard but particulate matter sometimes exceeds emission standard for a co-generation of heat and power plant. Atmospheric disperse model was used to calculate distribution of dioxin and inhalable risk model was used to assess exposure dosage of children and adults in the different distance downwind. In normal condition, the inhalable risk is not significant while the exposure dosage will exceed standard in accident conditions. It therefore is very important to control process safety for precaution of environmental risk.