Improved sludge dewaterability by combining SDS pre-treatment conditioning with PDMDAAC flocculation

Wastewater treatment generates considerable amounts of sludge. Reducing sludge volume by dewatering is an important part of many wastewater treatment processes. We investigated the effects of a combination of sodium dodecyl sulfate (SDS) and polydimethyldiallylammonium chloride (PDMDAAC) on anaerobically digested sludge dewaterability. Capillary suction time (CST) and specific resistance to filtration (SRF) were measured as indicators of sludge dewaterability. Extracellular polymeric substances (EPS) content, particle size, zeta potential, and bound water in sludge floc were also measured. We found that CST increased from 348.5 to 530.5 s as the SDS dosage increased. However, with a dose 0.03 g g(-1) DS PDMDAAC only, SRF and CST were 3.78 x 10(12) m kg(-1) and 79.2 s; with a combined dose of 0.025 g g(-1) DS SDS and 0.03 g g(-1) DS PDMDAAC, SRF and CST decreased to 3.21 x 10(12) m kg(-1) and 68.7 s. These results indicate that above a certain dose, SDS reduces sludge dewaterability and that an optimum dose of SDS in sludge pre-treatment would improve subsequent PDMDAAC conditioning. Sludge conditioned with a combination of SDS and PDMDAAC increases dewaterability more than conditioned with SDS only or PDMDAAC only. Freeing EPS-bound water with SDS followed by re-flocculation using PDMDAAC gave improvement in sludge dewaterability.