In-situ sludge reduction based on Mn²⁺-catalytic ozonation conditioning: Feasibility study and microbial mechanisms

To improve the sludge conditioning efficiency without increasing the ozone dose, an in-situ sludge reduction process based on Mn²⁺-catalytic ozonation conditioning was proposed. Using ozone conditioning alone as a control, a lab-scale sequencing batch reactor coupled with ozonated sludge recycle was evaluated for its operating performance at an ozone dose of 75 mg O₃/g VSS and 1.5 mmol/L Mn²⁺ addition. The results showed a 39.4% reduction in MLSS and an observed sludge yield of 0.236 kg MLSS/kg COD for the O₃+Mn²⁺ group compared to the O₃ group (15.3% and 0.292 kg MLSS/kg COD), accompanied by better COD, NH₄⁺-N, TN and TP removal, improved effluent SS and limited impact on excess sludge properties. Subsequently, activity tests, BIOLOG ECO microplates and 16S rRNA sequencing were applied to elucidate the changing mechanisms of Mn²⁺-catalytic ozonation related to microbial action: (1) Dehydrogenase activity reached a higher peak. (2) Microbial utilization of total carbon sources had an elevated effect, up to approximately 18%, and metabolic levels of six carbon sources were also increased, especially for sugars and amino acids most pronounced. (3) The abundance of Defluviicoccus under the phylum Proteobacteria was enhanced to 12.0% and dominated in the sludge, they had strong hydrolytic activity and metabolic capacity. Denitrifying bacteria of the genus Ferruginibacter also showed an abundance of 7.6%, they contributed to the solubilization and reduction of sludge biomass. These results could guide researchers to further reduce ozonation conditioning costs, improve sludge management and provide theoretical support.