New insight into filamentous sludge bulking during wastewater treatment: Surface characteristics and thermodynamics

Although there have been many studies on filamentary bulking of activated sludge, it has been revealed that there is still a gap in the microscopic mechanism of filamentary bulking. In this study, the surface characteristics and thermodynamics of sludge floc were investigated to reveal the mechanism of filamentous sludge bulking. The results showed that the EPS content gradually decreased from 71.09 mg/g VSS to 40.00 mg/g VSS and the protein (PN) content of the EPS significantly decreased from 64.10 mg/g VSS to 35.85 mg/g VSS during sludge bulking. The variation in the EPS and its components led to a decrease in the relative hydrophobicity of sludge and an increase in surface negative charge; then, deterioration of the flocculation setteability of sludge flocs occurred. The electric double layer (W_R) was the main force determining the aggregation of sludge during sludge bulking. The total energy of the interaction (W_T) increased during sludge bulking, which led to an increase in the difficulty of sludge accumulation. This study is useful for understanding the filamentous bulking of sludge within an activated sludge process.