Effects of Different Carbon and Nitrogen Ratios on Nitrogen Removal Efficiency and Microbial Communities in Constructed Wetlands

Abstract

Amidst rapid urbanization, municipal wastewater treatment plants remain a significant source of nitrogen compounds, which stems from their effluents. Constructed wetlands, employing denitrification processes, have been proven effective at nitrogen removal. Variations in influent nutrient concentrations are often seen as limiting factors affecting nitrogen removal and influencing microbial communities. This study evaluates the impact of nutrient limitation on nitrogen removal by analyzing changes in microbial communities within constructed wetlands under different influent water C/N ratios. The findings indicate that both excessively high and low C/N ratios constrain nitrogen decomposition, with optimal nitrogen removal observed at C/N ratios of 6 or 7. Moderate C/N values (6–7) support diverse and stable microbial networks, ensuring treatment system stability. Microorganisms play a pivotal role in nitrogen transformation, with the nirk gene being crucial for NH4+−N conversion, while the AOA gene dominates NO2−−N and TN conversion. This study offers practical guidance for identifying a suitable C/N ratio for wastewater treatment and establishes a theoretical foundation for regulating nitrogen removal by microbial communities in constructed wetlands within nitrogen removal systems.