Effect of organic matter on the expression of biochemical properties of partial nitrification immobilized filler and analysis of microbial communities

This study investigated the effect of organic matter on the partial nitrification (PN) performance of immobilized filler. When PN filler was put into an aerobic tank containing a large amount of organic matter for long-term operation, it resulted in efficient ammonia oxidation. Next, the PN filler was removed, and a continuous-flow PN reactor with artificial water distribution was constructed at laboratory scale to investigate the performance. The PN filler exhibited good resistance to the influence of organic matter. With the increase in influent chemical oxygen demand/total ammonia nitrogen (COD/TAN) from 0.04 to 1.25, the PN performance of the immobilized filler did not change. When the influent COD/TAN was increased to 3.22, ammonia-oxidizing bacteria (AOB) activity could be maintained by increasing the air supply. Batch experiments revealed that the reactor achieved simultaneous ammonia nitrogen (NH₄⁺-N) and COD removal, which indicated that AOB in the PN filler could compete better with heterotrophs to oxidize NH₄⁺-N using dissolved oxygen compared with traditional activated sludge and biofilm methods. Nitrite accumulation rate remained above 95 % throughout the reactor's operation. High-throughput sequencing showed that AOB were always the dominant bacteria in the microbial community inside the filler, and the high tolerance of PN filler to organic matter depended on AOB abundance. This study provides technical support for achieving efficient and stable PN in COD-containing wastewater.