Application of Reeds as Carbon Source for Enhancing Denitrification of Low C/N Micro-Polluted Water in Vertical-Flow Constructed Wetland

Abstract

Constructed wetlands have been applied to micro-polluted rivers and lakes. However, they often show poor nitrogen removal efficiency due to insufficient carbon sources for complete denitrification in the waters. In this study, a vertical-flow wetland system was built, in which reeds as a carbon source were added in the middle layer of the substrate. Thereby, the effect of the reed carbon source on denitrification of micro-polluted rivers and lakes with a low C/N ratio in the wetland and the denitrification mechanism were studied. The results showed that the concentrations of NH4+-N, NO3−-N and NO2−-N in the effluent of the constructed wetland were reduced to 0.17–0.35, 0.20–0.49 and 0.01–0.02 mg/L after adding the reed carbon source, and the removal efficiencies of the system for NH4+-N and NO3−-N reached 93.84% and 84.69%, respectively. The abundances of nirK, nirS, hzo and nrfA genes in the wetland substrate increased by 95.51%, 54.96%, 52.89% and 731.95%, respectively, which was considered to be related to the enhanced denitrification, anammox and dissimilatory nitrate reduction to ammonium of the wetland system. Reed planting promoted the increased abundances of amoA and nxrB genes, which might play a positive role in enhancing nitrification in wetland systems. The result of this study may provide a theoretical basis for the ecological restoration of low C/N micro-polluted water bodies.

Study on Phosphorus Removal Pathway in Constructed Wetlands with Thermally Modified Sepiolite

“…However, the application of constructed wetland technology worldwide has encountered many problems when dealing with nitrogen and phosphorus. Constructed wetlands have a good removal effect on COD (Chemical oxygen demand), BOD (Biochemical oxygen demand), SS (Suspended solids), and other pollutants, but the nitrogen and phosphorus removal effect is low [6][7][8]. According to reports, the nitrogen removal of most constructed wetlands is generally less than 30%, whereas the phosphorus removal of traditional constructed wetlands based on gravel is only approximately 15% [9,10].…”