Study of a New Photocatalytic Film Process Combined with a Constructed Wetland and an Analysis of Reoxygenation Pathways in a Water Body

Abstract

Pollution in water environments hinders both social progress and economic development. Wastewater treatment and the sustainable use of water resources are important factors in solving this problem. In a previous study, the authors proposed a process that used photocatalytic film as a back-end treatment in a composite iron–carbon constructed wetland (WIC&PF) to restore a mildly eutrophic water body. This method has strong reoxygenation effects, and can efficiently remove pollutants; these are qualities that have not been mentioned in previous studies regarding constructed wetlands. In this study, the authors further investigated the effectiveness of this process by using a photocatalytic film as a front-end treatment for a composite iron–carbon constructed wetland (PF&WIC) to restore a mildly eutrophic water body. The results showed NH4+-N, TN, TP, COD, and chlorophyll a removal rates using PF&WIC of 79.1 ± 6.6%, 76.8 ± 6.5%, 77.0 ± 5.4%, 77.3 ± 7.2%, and 91.7 ± 5.6%, respectively. The DO concentration of the water body increased compared with that of the effluent. The bacterial species and their abundance in the lake water also changed significantly, and photosynthetic autotrophic bacteria (Cyanobium PCC-6307) became the most dominant bacteria, and this played an important role in reoxygenating the water body. In comparing these results to those of our previous study, the removal of pollutants with PF&WIC was close to that with WIC&PF, but the reoxygenation effect of PF&WIC on the water body was significantly worse than that of WIC&PF; thus, WIC&PF is the more reasonable choice for treating eutrophic water bodies.