Unveiling the nitrogen removal performance from microbial network establishment in vertical flow constructed wetlands

The combined effects of substrate types (natural zeolite or shale ceramsite) and hydraulic retention time (HRT, 3-day or 6-day) on nutrient removal and microbial co-occurrence networks in vertical flow constructed wetlands (VFCWs) remains to be elucidated. In this study, zeolite-packed VFCWs demonstrated superior removal rates, achieving 93.65% removal of NH₄⁺-N and 83.84% removal of COD at 6-day HRT. The activity and establishment of microbial community were influenced by combined operating conditions. The abundances of Amx, amoA, nxrA, and nosZ genes increased with longer HRTs in zeolite-packed VFCWs. Additionally, a 6-day HRT significantly increased the relative abundances of Proteobacteria and Nitrospirae. At the species level, zeolite-packed VFCWs exhibited ecological niche sharing as a coping strategy in response to environment changes, while ceramsite-packed VFCWs displayed ecological niche differentiation. Both zeolite-packed and ceramsite-packed VFCWs established functional networks of nitrogen-transforming genera that utilized ecological niche differentiation strategies.