Integrated approach to enhance excess sludge degradation in microbial electrolysis cell: Role of ozone pretreatment.

Microbial electrolysis cell (MEC) is an alternative to conventional sludge treatment process with great energy-recovery potential. However, hydrolysis is considered as a rate-limiting step in MEC. In this study, ozone (O) pretreatment was successfully applied to disintegrate sludge matrix and accelerate microbial electrolysis. At 100-250 mg·g (O/SS), rapid SCOD increment and SS reduction rates were observed with increased O dosage. Afterwards, the mass transfer from gas to liquid was inhibited and oxidation reactions between O and organics occurred, which resulted in a declining disintegration rate. At favorable dosage of 250 mg·g (O/SS), the degree of disintegration was 17 % and SS reduction reached 44.9 %. A lab-scale MEC experiment was performed by feeding ozonated sludge. Results showed that O pretreatment yielded 8.3-times increment in biogas production rate. In addition, O pretreatment improved the organics removal and bioelectrochemical efficiency during microbial electrolysis, achieving 74.50 % of VSS removal rate and 77.56 % of TCOD removal rate, with gas yield increased by 7.5 times and cathodic hydrogen recovery increased by 7.40 %. The FT-IR spectra indicated negligible difference between influent extracellular biological organic matter (EBOM) and effluent EBOM, which suggested the function of O pretreatment was to accelerate microbial electrolysis reactions due to sludge disintegration. Furthermore, the ozonation pretreatment facilitated the enrichment of exoelectrogens and collaborative bacteria in MEC, collectively enhancing MEC performance. This study provides a theoretical reference for enhanced bioelectrochemical treatment of complex heterogeneous mixture with soluble/insoluble organic matters.