Abstract
Micro-polluted surface waters (MPSWs) draw increased concern for environmental protection. However, traditional treatment methods such as activated sludge, ozone activated carbon, and membrane filtration suffer from high cost and susceptibility to secondary pollution and are rarely used to address MPSWs. Herein, a new stepped combined constructed wetland planted with Eichhornia crassipes without additional inputs was developed. In a 60-day experiment conducted in a drainage canal, we evaluated contaminant removal and bacterial communities using laboratory analysis and amplicon sequencing. Our results showed that the stepped combined constructed wetland achieved impressive removal rates for various contaminants. It was able to remove 70% of suspended solids, 51% of total nitrogen, 55% of total phosphorus, 70% of ammonia nitrogen, and 64% of the chemical oxygen demand. The dominant bacterial phyla found in stepped combined constructed wetland was Proteobacteria and Actinobacteria, with average relative abundances of 43.4 and 19.9%, respectively. We also observed clear differences in bacterial genera between the influent and effluent water samples. Specifically, we found that the stepped combined constructed wetland significantly reduced the abundance of bacteria such as hgcl clade, Rhizorhapis, and Cyanobacteria, while increasing the abundance of bacteria like Flavobacterium, Limnohabitans, Alpinimonas, Erwinia, and Saccharibacteria. The dominant bacterial community comprised nitrifying bacteria (Azoarcus and Nitrospira), denitrifying bacteria (e.g., Mycobacterium, Paracoccus, Ralstonia, Rhodobacter, Escherichia Shigella), and nitrogen-fixing bacteria (Rhizobium, Bradyrhizobium, Azospirillum). Notably, the abundance of nitrogen-fixing bacteria, nitrite-oxidizing bacteria, and denitrifying bacteria increased with the stepped combined constructed wetland presence. The stepped combined constructed wetland technology is highly cost-effective, with a total investment of only 259.83 USD. The majority of this investment is used for construction, with minimal expenditure required for operation and maintenance. Therefore, the stepped combined constructed wetland presents an economical and environmentally friendly solution for pollutant removal in slow flow and still water areas. It offers numerous benefits, including improved pollutant removal efficiency, low cost, ecological advantages, and extensive development potential, in various fields.