Investigating the addition of Fe for improving contaminant removal and regulating microbes in a simulated coastal wetland.

Contaminants from wastewater of aquaculture are increasing the risks of red tides in coastal areas. Such types of contaminants are difficult to remove by using conventional biological and ecological treatment methods because of the relatively low C/N ratios and the high salinity in coastal water ambience. Fe is considered a key element in natural chemical cycling and promotes the growth of animals and plants as well. The cycling of Fe ion combined with carbon, nitrogen, and phosphorus stimulates bacterial growth. As a result, it acts as a microbial carbon pump in coastal areas, such as natural wetlands, which have been activated and adapted to be salinity resistant and insufficient energy supply. Along these lines, in this work, constructed wetlands (CWs) with high ecological benefits and low cost of maintenance were used to treat aquaculture wastewater. The impact of Fe ion recycling on multiple contaminants was also systematically investigated. The two types of Fe dosage were pure ferrous ions and a mixture of iron powder and ferrous ions. After the application of a 3-day treatment, the dosage of iron powder/ferric ions (1:1 m/m) at a concentration of 15 mg L showed a better effect, where the total nitrogen, total phosphorus, and chemical oxygen demand removal rates were increased by 2.95%, 2.16%, and 9.76%, respectively. From the microbial analysis, it was indicated that Fe ion affected the abundance and functions of the microbial communities in the CWs. The significant enrichment of Proteobacteria promoted the removal of multiple contaminants under saline stress and fixed carbon, and affected the whole microbe distribution and diversity in CWs. The implementation of such an environmentally friendly and economical approach arises as a promising candidate for the efficient removal of multiple contaminants from aquacultural wastewater in coastal zones.