Novel Stepped Combined\nConstructed Wetland For Surface\nWater Removal: Enhancing the Performance and Responses of Microbial\nCommunities

Micro-polluted surface waters (MPSWs) draw increased\nconcern for\nenvironmental protection. However, traditional treatment methods such\nas activated sludge, ozone activated carbon, and membrane filtration\nsuffer from high cost and susceptibility to secondary pollution and\nare rarely used to address MPSWs. Herein, a new stepped combined constructed\nwetland planted with Eichhornia crassipes without additional inputs was developed. In a 60-day experiment\nconducted in a drainage canal, we evaluated contaminant removal and\nbacterial communities using laboratory analysis and amplicon sequencing.\nOur results showed that the stepped combined constructed wetland achieved\nimpressive removal rates for various contaminants. It was able to\nremove 70% of suspended solids, 51% of total nitrogen, 55% of total\nphosphorus, 70% of ammonia nitrogen, and 64% of the chemical oxygen\ndemand. The dominant bacterial phyla found in stepped combined constructed\nwetland was Proteobacteria and Actinobacteria, with average relative\nabundances of 43.4 and 19.9%, respectively. We also observed clear\ndifferences in bacterial genera between the influent and effluent\nwater samples. Specifically, we found that the stepped combined constructed\nwetland significantly reduced the abundance of bacteria such as <i>hgcl clade</i>, <i>Rhizorhapis</i>, and <i>Cyanobacteria</i>, while increasing the abundance of bacteria like <i>Flavobacterium</i>, <i>Limnohabitans</i>, <i>Alpinimonas, Erwinia</i>, and <i>Saccharibacteria</i>. The dominant bacterial community\ncomprised nitrifying bacteria (<i>Azoarcus</i> and <i>Nitrospira</i>), denitrifying bacteria (e.g., <i>Mycobacterium</i>, <i>Paracoccus</i>, <i>Ralstonia</i>, <i>Rhodobacter</i>, Escherichia Shigella), and nitrogen-fixing bacteria (<i>Rhizobium</i>, <i>Bradyrhizobium</i>, <i>Azospirillum</i>). Notably,\nthe abundance of nitrogen-fixing bacteria, nitrite-oxidizing bacteria,\nand denitrifying bacteria increased with the stepped combined constructed\nwetland presence. The stepped combined constructed wetland technology\nis highly cost-effective, with a total investment of only 259.83 USD.\nThe majority of this investment is used for construction, with minimal\nexpenditure required for operation and maintenance. Therefore, the\nstepped combined constructed wetland presents an economical and environmentally\nfriendly solution for pollutant removal in slow flow and still water\nareas. It offers numerous benefits, including improved pollutant removal\nefficiency, low cost, ecological advantages, and extensive development\npotential, in various fields.