Advanced anaerobic digested sludge dewaterability enhancement using sludge based activated carbon (SBAC) in combination with organic polymers

Abstract

Wastewater sludge is difficult to dewater because the extracellular polymeric substances (EPS) it contains are highly hydrated and sticky. Anaerobic digestion generally results in further deterioration of sludge dewaterability due to the release of large quantities of biopolymers and fine particles. Chemical conditioning is required prior to mechanical dewatering and is of great importance in the operation of the dewatering process. In this work, a novel anaerobically digested (AD) sludge conditioning process that combines sludge based activated carbon (SBAC) as a skeleton builder with organic polymers (cationic polyacrylamide, CPAM, and chitosan, CTS) for flocculation is proposed to simultaneously remove soluble biopolymers and improve sludge dewaterability. Results indicate that the specific resistance to filtration (SRF) of AD sludge was decreased and that tryptophan-like proteins and humic substances in soluble EPS and loosely-bound EPS were effectively removed by SBAC adsorption through hydrophobic interaction. Flocs formed through CTS conditioning were smaller but aggregated more strongly and formed less compressible cake than those formed through CPAM conditioning. SBAC and cationic organic polymers showed a significant synergistic effect in improving sludge dewatering. The incorporation of SBAC into conditioning with organic polymers increased the strength of sludge floc aggregation and improved recover ability from mechanical shearing. Confocal laser scanning microscopy showed that conditioning with SBAC in combination with organic polymers resulted in protein molecules forming large aggregates, while polysaccharide molecules were uniformly distributed in sludge floc. This work provides a green and promising strategy for improved AD biosolid dewatering using sludge based activated carbon in combination with CTS.