Feasibility of sludge deep-dewatering with sawdust conditioning for incineration disposal without energy input

- Sawdust conditioning (SC) is feasible in deep-dewatering for sludge incineration.
- SC can decrease sludge moisture content, but finitely accelerate dewatering rate.
- SC can efficiently accelerate sludge cake further dewatering via air drying.
- SC improves the calorific value of sludge cake and makes incineration profitable.

Sludge deep-dewatering could be realized by adding inorganic and chemical conditioners. However, once for the purpose of incineration disposal, the uses of inorganic and chemical conditioners would not only bring about incomplete combustion, equipment corrosion and secondary pollution, but also greatly reduce the heat value of sludge cake. Therefore, the feasibility of sludge deep-dewatering with sawdust conditioning was investigated for incineration disposal without energy input. Firstly, the performance and mechanism of sludge deep-dewatering were studied when conventional conditioners, lime and polyacrylamide, were substituted by sawdust. Then, the superiorities of sawdust conditioning in sludge cake air drying and calorific value increase, as well as economic efficiency were analyzed by comparing with lime conditioning. Results indicate the moisture content of sludge cake can be greatly reduced by sawdust conditioning, which could decrease sludge compressibility, reduce bound water content, improve the porosity of sludge cake, but scarcely influence sludge particle size. Moreover, sawdust conditioning presented high efficiency in further dewatering of sludge cake during natural air drying. The moisture content of sludge cake conditioned with sawdust could decrease to 31.6% after 36 h air drying and its calorific value reached as high as 2239 kcal/kg. By comparing with lime conditioning, sawdust conditioning exhibited slightly higher expense for the conditioner, but much greater profit from energy recovery.