Abstract:The extraction of rare earth elements through the ammonium sulfate leaching process has resulted in significant nitrogen pollution in the groundwater of rare earth mines. Address to the characteristics of groundwater in rare earth mines, characterized by high ammonia nitrogen concentration, strong acidity, and high concentration of heavy metal ions, a heterotrophic nitrification-aerobic denitrification (HNAD) high-efficiency denitrification reactor was constructed by using corncob, ceramite and cement as composite fillers. The denitrification performance and mechanism of HNAD in rare earth mine groundwater treatment under the coupling effect of composite fillers were studied. The results demonstrate that the removal rates of NO3--N and NH4+-N can be stabilized at over 94.20% and 81.22% within 23 days, respectively. Furthermore, the reactor can provide an alkaline environment conducive to denitrification. FT-IR and CLSM analyses demonstrate that utilizing corncob as a slow-release carbon source allows the composite filler to offer effective attachment points for microorganisms, facilitating the generation of stable extracellular polymers (EPS) that promote denitrification. The results of microbial diversity analysis indicate that Thauera and Treponema are capable of adapting to the groundwater environment found in rare earth mines, and they represent the primary denitrifying microorganisms present in the reactor. This study offers a theoretical foundation and technical guidance for the application of HNAD in the groundwater of rare earth mines.