Enhanced nitrogen removal driven by S/Fe2+ cycle in a novel hybrid constructed wetland

Insufficient carbon sources and oxygen limit the nitrogen removal efficiency of constructed wetlands. In this study, a novel hybrid constructed wetland (SS-HCW) was designed by combining sulfur-siderite filler and drop aeration to enhance nitrogen removal. The results showed that the TN removal rate increased by 37.74%. Further analysis of nitrogen removal pathways found that sulfur autotrophic denitrification was dominant. In addition, SO42− and Fe2+ generated during nitrogen removal can serve as trace elements to increase the growth rate and chlorophyll content of wetland plants by 50.0% and 34.2%, respectively. The microbial analysis results showed that the sulfur-siderite filler changed community structure, with Thiobacillus and Sulfurimonas as the dominant genera, and enriched some bacteria with sulfur and iron oxidation capabilities such as Thiomonas and Ferritrophicum. [Display omitted] •Sulfur-siderite filler and drop aeration were coupled in a hybrid constructed wetland.•Sulfur-siderite filler optimized the nitrogen removal path and increased the TN removal rate by 37.74%.•SO42− and Fe2+ increased plant chlorophyll content and growth rate by 34.2% and 50.0%.•Sulfur-siderite filler promoted the growth of nitrogen removal functional bacteria.