Enhanced treatment of low C/N ratio rural sewage by a modified multi-stage tidal flow constructed wetland at low temperature: Quantitative contributions of key functional genera.

Rural sewage treatment was traditionally faced contradiction between low-treatment rates and the need for low-cost development. To address this challenge, we explored the coupling of effluent circulation and step-feeding strategies in a multi-stage tidal flow constructed wetland (TFCW) to achieve stable nitrogen (N) removal performance under conditions of low carbon-to-nitrogen (C/N) ratios and low temperatures. The modified multi-stage TFCW demonstrated the ability to significantly reduce the concentrations of effluent NH4+-N and NO3--N by 33.9 % and 54.8 % respectively, resulting in values of 7.47 mg/L and 3.93 mg/L. Additionally, it achieved an average TN removal efficiency of 69.2 %. The improved N removal performance of rural sewage by the modified multi-stage TFCW at low temperatures was primarily attributed to autotrophic nitrification, heterotrophic nitrification, and autotrophic denitrification. Among the identified functional genera, Nitrosomonas and Nitrosospira played key roles as autotrophic nitrification bacteria (ANB), contributing to 28.2 % of NH4+-N removal. The key heterotrophic nitrification bacteria (HNB) Acidovorax and Rudaea were mainly responsible for 71.3 % of NH4+-N removal via the two-step ammonia assimilation through the organic nitrogen pathway. Furthermore, Rhodanobacter and Acinetobacter emerged as key autotrophic denitrification bacteria (ADNB), accounting for 79.9 % of NO3--N conversion and removal. In summary, this study provides valuable theoretical insights and supports ongoing efforts in biological regulation to address the challenges associated with rural sewage treatment.