Non-point source polluted river changes microbial community assembly and improves pollutant transformation ability of constructed wetland

Abstract

Non-point source pollution has become a critical factor in water pollution in China with the improvement of point-source pollution control technologies and strengthening of supervision. This study introduced non-point-source-polluted rivers in industrial parks into a constructed wetland (CW) with advanced treatment units to effectively treat the polluted rivers. Although the pollutant load of the CW initially increased, after 100 days of adaptation, the removal rates of total nitrogen and organic carbon in the CW were greater than 96.99% and 84.74%, respectively. The effluent water complied with the China Environmental Quality Standards for Surface Water Standards (GB 3838-2002) Class IV. Introducing non-point-source-polluted river water increased the richness, diversity, and complex functional potential of the microbial community in CW, which improved system stability. The reduction in industrial pollutant stress and improvement of the nutritional environment are the main driving factors for the reorganization of microbial communities in CWs. The community composition shifted from being dominated by industrial pollutant-tolerant microorganisms such as Cyanobacteria and Actinobacteria to a more diverse array of microorganisms, including Bacteroidetes, Chloroflexi, and Firmicutes. Before the CW reconstruction, nitrification and acetyl-CoA conversion may be the main rate-limiting steps in carbon and nitrogen conversion in industrial wastewater CWs. These processes may have been limited because of oligotrophic conditions and industrial pollutant stress. The introduction of rivers polluted by non-point sources alleviates these constraints, thus increasing the treatment potential of the CW system. This paper provides a case study for the collaborative treatment of point and non-point source pollution in industrial parks. This study provides valuable guidance for effectively managing and reconstructing CWs in industrial environments.