Electrochemical pretreatment for stabilization of waste activated sludge

Abstract

Stabilization of waste activated sludge (WAS) is an essential step for the disposal or reuse. In this study, WAS stabilization via electrochemical pretreatment (EPT) at 0–15V was evaluated for simultaneous dewaterability enhancement, pathogen removal and H₂S mitigation. The mechanism underlying EPT was investigated and discussed based on the changes in the physicochemical (e.g., particle size, zeta potential, hydrophobicity and extracellular polymeric substances) and biological characteristics (i.e. cell morphology, and distribution and percentages of live/dead cells) of WAS with different EPT voltages. The results revealed that EPT disintegrated WAS flocs and disrupted the cell walls leading to a reduction in particle size (by up to 50%), increased release of extracellular and intracellular substances (by up to 4 times) to facilitate WAS stabilization. With EPT at 15V, the capillary suction time of WAS decreased by 42%, and the concentrations of E. coli and indicator pathogens (Salmonella spp. and Streptococcus faecalis) fell by nearly 5 log₁₀ reaching U.S. EPA hygienization levels. Furthermore, EPT at 12V or higher suppressed the amounts of dissolved sulfide and H₂S_(g) produced from the WAS under anaerobic conditions by over 99%. This study demonstrates the feasibility of EPT for simultaneous WAS dewaterability enhancement, pathogen inactivation and H₂S mitigation, providing a one-step alternative for sludge stabilization.