The optimized operation mode in mature landfill leachate treatment based on EEM-PARAFAC-SOM

Mature leachate demonstrates low biodegradability due to the increase of recalcitrant substances during the landfill process. Development of tolerant membrane bioreactor (MBR) and catalytic ozonation coupled system is crucial for the deep treatment of leachate. By optimizing the treatment system, this study developed three operation modes including internal circulation (Mode 1, 1st–10th day), MBR-catalytic ozonation (Mode 2, 11th–30th day), and catalytic ozonation-MBR (Mode 3, 31st–58th day), and explored their treatment effects on leachate. The results showed that during Mode 1, the removal rate of NH₄⁺-N reached 99.6 %, and the COD removal rate exceeded 80 %. Mode 2 and Mode 3 achieved COD removal rates of 92.4 % and 96.6 % respectively, among which the effluent of Mode 3 met the discharge standards. The FRI removal rates of five types of organic matter were more than 95 %. Catalytic ozonation could first oxidize and decompose large-molecule organic substances into relatively small-molecule and easily degradable organic substances, which were then degraded and utilized by microorganisms in the MBR system. The relative abundance of Proteobacteria increased from 37.95 % to 75.27 %, and it was the main body for degrading organic matter and denitrifying nitrogen. The abundance of unclassified Rhodobacteraceae significantly increased from 1.33 % to 30.16 %. By degrading the organic matter in the leachate, it controlled the accumulation of NO₂^–-N and NO₃^–-N in synergy with the denitrifying bacterial community. This research offered reference for the continuous treatment of leachate and improved understanding of evolution of bacterial community, bringing it much closer to practical application.