Consolidation dewatering and centrifugal sedimentation of flocculated activated sludge

This study investigated experimentally the consolidation dewatering and centrifugal-settling processes for activated sludge subjected to cationic polyelectrolyte flocculation. The results were reported for the dynamic response of sediment cake thickness (an index for cake compaction) under various doses of polyelectrolyte conditioning, compression-permeability cell configuration and mode of operation (batch and continuous) in a centrifugal-settling cell. The reduction in sediment thickness of sludge by consolidation and centrifugation was found to correspond mostly well with the optimal dose of polyelectrolyte based on the capillary suction time. The relaxation/rebound of cake thickness was observed in both consolidation dewatering and centrifugal dewatering with comparable compaction/relaxation time scale ratios. The equilibrium sediment consolidation ratio increases with the effective solid pressure characterized by P-m and P-s, for the consolidation dewatering and centrifugal sedimentation, respectively. The experimentally determined time scales of the cake consolidation dewatering/centrifugal sedimentation processes agree reasonably well with the theory by Landman and Russel (Phys. Fluids A 5 (1993) 550). (C) 2003 Elsevier Science Ltd. All rights reserved.