Effect of combined dialysis method on dewatering of coagulant pretreated sludge

The unique composition and condition of sludge pose significant challenges in water removal. Therefore, it is crucial to investigate a cost-effective and highly efficient approach for dehydrating sludge. In this paper, the domestic sludge was respectively pretreated with ferric chloride, polyaluminum chloride, and cationic polyacrylamide. Then the pretreated sludge was performed on gravity dehydration, centrifugal dehydration, dialysis dehydration and mixed method. The effect mechanism of coagulant and dewatering method on sludge dehydration was analyzed from micro perspective. Finally, the influence range of the dialytic solution was tested by model experiment. The results indicate that the dehydration efficiency of the pretreated sludge with PAC is slightly better than that pretreated with FeCl3 and CPAM, and the optimal dosage of PAC is 8 %. The effect of dialysis dehydration is the best, which can significantly change the final moisture content of sludge (much less than 60 %), effectively achieving the requirements of subsequent processing. The water content of the sludge treated by gravity dehydration, centrifugal dehydration and dialysis dehydration can reach 38 %, which is much smaller than that of the sludge treated by a single dehydration method. The free water, occlusion, coating water, and bounding water are dehydrated by gravity, centrifugal force, and dialysis. The influence range of dialysis dehydration is less than 10 cm. When the distance is more than 10 cm, the difference of sludge moisture content at different relative heights is larger. The study has certain theoretical guidance significance for improving the performance of sludge concentration and dewatering.