Fate of extracellular polymeric substances of anaerobically digested sewage sludge during pre-dewatering conditioning with Acidithiobacillus ferrooxidans culture

• Rapid flocculation of sewage sludge was achieved using iron-oxidizing bacteria.
• A. ferrooxidans biogenic flocculant significantly improved the sludge dewatering.
• A rapid reduction of EPS content was achieved during sludge flocculation.
• Positive correlation between EPS reduction and sludge dewaterability was observed.

This study investigated the fate of extracellular polymeric substances (EPS) of anaerobically digested saline sewage sludge during its preconditioning. Sludge was conditioned with Acidithiobacillus ferrooxidans (AF) culture for 24 h in the presence and absence of Fe2+ as an energy substrate. pH decreased from 7.24 to 3.12 during sludge conditioning process. The capillary suction time (CST) of conditioned sludge significantly decreased to <10 s, and specific resistance to filtration (SRF) was reduced by >94% as compared with control within 4 h of conditioning with or without Fe2+, indicating a significant (P < 0.001) improvement in sludge dewaterability. A noticeable decrease in extractable EPS was observed in conditioned sludge. The EPS contents showed a significant negative correlation with dewaterability of sludge (P < 0.05). The results suggest that bioacidification treatment using A. ferrooxidans effectively improved sludge dewaterability through modification of sludge EPS.