Effects of nitrogen removal microbes and partial nitrification-denitrification in the integrated vertical-flow constructed wetland

•Increasing the influent C/N ratio could improve the N removal efficiency of IVCW.•A relationship exists between the N removal genes and water quality parameters.•Partial nitrification-denitrification occurred in IVCW under the high C/N ratio.

In this study, the treatment performance of the integrated vertical-flow constructed wetland (IVCW) and nitrogen (N) removal mechanism of microbes were explored by quantitative PCR (qPCR) technology. The results showed that the IVCW pilot system could achieve high removal efficiencies of NH4+-N (above 90%), TN (55–90%) and TOC (above 95%) under 2, 4, 6, 8 C/N ratios. A close relationship exists between the abundance of nitrogen-removing microbes and water quality parameters of effluents. The abundance of bacterial 16S rRNA genes, amoA of ammonia oxidizing bacteria (AOB), nirS of denitrification bacteria and nxrA of nitrite oxidizing bacteria (NOB) in the down-flow chamber were higher than those of the up-flow chamber in IVCW. The relative abundance of amoA, nirS and nxrA suggested that AOB and denitrification bacteria were predominant in the nitrogen removal process, and thus the partial nitrification and denitrification appeared to be the main N removal process in the IVCW test system.