Unraveling the mechanism of dissolved organic matter in enhancing nitrogen removal from leachate wastewater treatment via aerobic granular sludge process.

The aerobic granular sludge (AGS) process has emerged as a viable alternative to landfill leachate treatment. The mechanisms by which dissolved organic matter (DOM) in landfill leachate, a potential stimulant, is utilized during treatment with AGS systems remain unclear. In this study, we revealed DOM-mediated nitrogen removal in AGS receiving the effluent from up-flow anaerobic sludge blanket (UASB). The results showed that granules were successfully formed with real fresh leachate contents increasing from 10% to 30%. The established AGS bioreactor could achieve good nitrogen removal (76.16% on average) through partial nitrification-denitrification (PND), effectively reducing carbon demand and selectively utilizing DOM from leachate. Fourier transform ion cyclotron resonance mass spectrometry analysis showed the utilization of DOM of aliphatic, protein-like and amino sugar-like compounds with low saturation in situ of leachate. Microbial analysis identified that Thauera and Rhodobacter belong to Proteobacteria as the dominant nitrogen-removing bacteria, and OLB13, OLB12, and Devosia, accounting for 16.11% of the microbial community, are the primary DOM degraders, with significant correlation (p < 0.05). High-throughput analysis showed that protein-like and amino sugar-like compounds were the main DOM components used to facilitate PND via diverse metabolic pathways. This study suggests that the critical role of DOM interactions with AGS microbial consortia could shed light on the regulation of nitrogen removal in landfill leachate treatment.