Optimization of biochemical oxygen demand to total nitrogen ratio for treating landfill leachate in a single-stage partial nitrification-denitrification system

Abstract In this study, a partial nitrification-denitrification (PND) system was established to treat landfill leachate with different influent biochemical oxygen demand to total nitrogen ratio (BOD/N = 0.73, 2.27 and 1.44). The long-term operation results showed the highest TN removal rate of 226 mg/(L·d) have been stably obtained under influent BOD/N of 1.44. Additionally, the influent BOD/N affected the composition and content of the extracellular polymeric substances (EPS) in the sludge, especially the humic acid-like matter in tightly bound EPS (TB-EPS), thus affecting the sludge sedimentation and the system performance. The higher the influent BOD/N, the better the sludge sedimentation. At the micro-level, the microbial community evolved markedly under different influent BOD/N and Ottowia was the dominant genus in the system. At an influent BOD/N of 1.44, the relative abundance of aerobic denitrifying bacteria and mixotrophic denitrifying bacteria was highest, which ensuring the system has a good PND performance of the system. Overall, the results of this study clarified the effects and mechanisms of different BOD/N on the PND system and provided theoretical basis and technical reference for practical engineering application.