Augmentation of Nitrogen Removal Efficiency of Aerobic Denitrifying Bacterial Communities by Inorganic Electron Donors via Enclosure Experiments

During the long-term operation of reservoirs, significant accumulation of pollutants occurs under static hydraulic conditions, profoundly influencing the distribution of nitrogen, phosphorus, organic matter, and other contaminants in water bodies. This study addressed the nitrogen pollution issue in the Jinpen Reservoir of the Heihe River by employing sponge iron-activated carbon as an inorganic electron donor and polyurethane sponge as a microbial carrier to investigate aerobic denitrification for nitrogen removal. Further analysis of microbial community structure and quantitative polymerase chain reaction (qPCR) were conducted to explore the characteristics of inorganic electron donor-driven aerobic denitrification for nitrogen removal. The results demonstrate that water pollutants are continuously reduced during the operation of the pilot enclosure system. In the first operational cycle (40 days), the total nitrogen concentration decreases from 1.39 mg/L to 0.847 mg/L, achieving a removal rate of 39.06%, while the NO₃^--N concentration declines from 1.077 mg/L to 0.761 mg/L, corresponding to a removal rate of 29.34%. During the second cycle, the total nitrogen concentration decreases from 2.591 mg/L to 1.895 mg/L, representing a reduction of 0.696 mg/L and a removal rate of 26.86%. Similarly, the NO₃^--N concentration drops from 2.559 mg/L to 1.849 mg/L, with a removal rate of 27.74%. These findings confirm the efficacy of the pilot system in eliminating water pollutants. Additionally, high-throughput sequencing and absolute quantitative analyses reveal that system operation alters microbial distribution and synergistic interactions, stimulating the expression of functional enzymes critical to pollutant degradation. This study provides a feasible strategy for in-situ bioremediation of contaminated water bodies.