Fate of extracellular polymeric substances during flocculation of anaerobically digested sludge using biogenic flocculant

Abstract

This study investigated the fate of extracellular polymeric substances (EPS) of anaerobically digested saline sewage sludge during its conditioning with a biogenic flocculant produced by Acidithiobacillus ferrooxidans culture before dewatering. Sludge was conditioned for 24h with the biogenic flocculant in presence and absence of Fe2+ as energy substrate. During the sludge conditioning process, pH dropped from 7.24 to 3.12. The capillary suction time of sludge was <10s and specific resistance to filtration (SRF) was reduced by more than 94% of its original SRF in the biogenic flocculent treatments within 4h of incubation with or without FeSO4 indicating a significant (P<0.001) improvement in sludge dewaterability. A significant decrease in extractable EPS was observed in treatments with biogenic flocculant and the EPS contents showed a significant negative correlation with dewaterability of sludge (P<0.05). The results suggest that the biogenic flocculant effectively improved sludge dewaterability through modification of sludge EPS.