Study on the Purification Treatment of Industrial Wastewater Discharge in the Upper Yangtze River Using Biological Nitrogen Removal Technology

Abstract

The wastewater from factories in the upper Yangtze River has a low carbon-to-nitrogen (C/N) ratio, which poses a great difficulty for biological nitrogen removal. This article took a wastewater treatment plant in the upper Yangtze River as an example to analyze the effect of the addition of an iron source (Fe²⁺) on biological nitrogen removal under low C/N ratios. Two sequencing batch reactors were set up for comparison: system A had an influent C/N ratio of 2, while system B had an influent C/N ratio of 5. The experiment operated in three stages, each lasting 28 days. In stage 2, 1 mg/L of Fe²⁺ was added, and in stage 3, 2 mg/L of Fe²⁺ was added. It was found that system B maintained good nitrogen removal performance at a C/N ratio of 5. In contrast, system A achieved 88.21 ± 8.97% ammonia nitrogen removal at day 7, 91.64 ± 6.86% at day 56, 95.01 ± 6.33% at day 84, and 30.21 ± 9.87% total nitrogen removal at day 7, 38.45 ± 8.25% at day 56, 43.56 ± 7.33% at day 84, demonstrating the improvement effect of Fe²⁺ on nitrogen removal performance under low C/N ratios. In terms of microbial population distribution, the addition of Fe²⁺ promoted the growth of nitrifying and denitrifying functional bacterial communities. The results demonstrate the improved effect of the external iron source (Fe²⁺) on biological nitrogen removal technology, which could be applied in actual wastewater purification treatment.