Carbon source deficiency is the crucial factor constraining conventional biological nitrogen removal in low C/N wastewater. Therefore, this study investigated nutrients and dimethyl phthalate (DMP) removal and mechanisms in an algal pond-constructed wetland system treating wastewater at different low C/N ratio. The findings indicated that the system exhibited optimal comprehensive treatment performance at a C/N ratio of 5. Under this condition, the removal efficiencies of ammonia nitrogen, total nitrogen and DMP reached 98.5%, 56.8% and 78.0%, respectively, while nitrous oxide emissions were significantly reduced. Scenedesmus obliquus exhibited good growth. Meanwhile, extracellular polymeric substances (EPS) secreted by microorganisms were mainly soluble EPS, which served as a slow-release carbon source to supplement the electron donors required for denitrification and enhanced DMP biodegradation. Although an elevated C/N ratio reduced microbial community biodiversity and abundance, it significantly enhanced the relative abundance of functional microbes related to nitrogen transformation. Notably, the levels of denitrification functional genes ( norB , nosZ, nirK , nirS ) all improved, indicating enhanced genetic and metabolic potential for denitrification. These findings indicate moderately optimizing the influent C/N ratio can effectively and synergistically remove multiple pollutants and reduce greenhouse gas emissions in the integrated system, offering a theoretical foundation for the co-treatment and ecological remediation of multiple pollutants in low C/N wastewater. • TN and DMP removal reached 57% and 78% with N 2 O emissions halved at C/N=5. • Soluble-EPS served as the main carbon source for denitrification. • Denitrifying microbial community richness increased at the low C/N ratio. • Low C/N ratio increased the relative abundance of denitrification genes.
Fan et al. (Sun,) studied this question.