Sludge dewaterability improvement in microbial fuel cell powered electro-Fenton system (MFCⓅEFs) coupled with chitosan quaternary ammonium salt

As improved and expanded wastewater treatment facilities, sludge dewatering is the essential process and major challenge due to the complex and abundant organic matter. Microbial fuel cell powered electro-Fenton system (MFCⓅEFs) has been demonstrated to generate •OH and destroy hydrophilic extracellular polymeric substances (EPS) as an improved method of high efficiency and low energy consumption. Nevertheless, the smaller particle size of the treated sludge and the release of partial organic matter into the supernatant can affect the sludge-water separation process. Chitosan quaternary ammonium salt (CQAS) as a renewable and biodegradability cationic coagulant can be involved in the follow-up treatment. The sludge after combined treatment exhibited better dewaterability, where the water content of sludge cake (WC_SC), capillary suction time (CST), and specific resistance filtration (SRF) were 61.21%, 15.6 s, and 1.02×10¹² m/kg (26.47%, 80.72% and 84.28% reduction), respectively. The oxidation of the MFCⓅEFs destroyed the cellular and EPS structure and the bridging flocculation and charge neutralization of CQAS caused the fine particles to squeeze each other. The combined treatment fully reduced the content of negative charge and hydrophilic substances on the surface, which affected the intensity change of N-H bond and altered the protein secondary structure to make it looser, thus releasing more bound water while improving aggregation characteristics. Overall, combined treatment can significantly improve sludge dewaterability and owns operational advantages of high efficiency, low energy and consumption, safety, and non-toxicity.