Coupled effects of initial water content with refrigeration temperature and freeze-thaw cycles on dewatering of sludge.

Many studies have displayed that freeze-thaw (F/T) conditioning is an environmentally friendly approach of improving sludge dewaterability. However, Initial water content (IWC) has a strong influence on the efficiency of the F/T method in conditioning sludge dewatering performance. Finding the most suitable F/T parameters for sludge with different IWCs is a critical issue that needs to be solved. Therefore, the coupled effects of different IWCs, refrigeration temperatures and the number of F/T cycles on sludge dewatering characteristics were explored. Single and multiple F/T cycles were performed on sludge from each group of IWCs at the same temperature. The coupling mechanism was analyzed by comparing the changes in sludge dewatering capacity before and after conditioning. The outcomes show that the F/T method is more suitable for sludge with a higher IWC. At -28 °C, the specific resistance to filtration of sludge with 87.5% IWC was reduced to 65.8 × 10 m/kg, and the post-filtration water content was only 63.1%. After repeated F/T cycles, the water content of the sludge gradually decreased, and the post-filtration water content of sludge with 87.5% IWC dropped to 58.8% after 7 cycles. Appropriate refrigeration temperatures can improve the effectiveness of ice crystal cracking, especially for sludge with a water content of less than 82.5%. The results of research provide a guide for the selection of F/T parameters in the operation of deep dewatering of sludge with different IWCs.