Multi-metabolism pathways insights into nutrients removal performance with adding heterotrophic nitrification-aerobic denitrification bacteria in tidal flow constructed wetlands

Constructed Wetlands (CWs) usually exhibit limits in functional redundancy and diversity of microbial community contributing to lower performances of nutrients removal in decentralized domestic sewage treatment. To address this quandary, heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria was added in tidal flow CWs (TFCWs) developing for enhanced removal of nitrogen (N) and phosphorus (P) from decentralized domestic sewage. TFCWs could be set-up more rapidly by enhancement of HN-AD bacteria with removal efficiencies of 66.9%~70.1% total nitrogen (TN), and 88.2%~92.4% total phosphorus (TP) during stable operation. Typical-cycles variations showed TFCWs with addition of HN-AD bacteria promoted NO3--N and NH4+-N removal respectively under hydraulic retention time (HRT) of 14 h and 8 h with slight NO2--N accumulation. Activated alumina (AA) coupled with HN-AD bacteria decreased P release and relieved its poor removal performance in CWs. Based on metagenomic taxa and functional annotation, Pseudomonas and Thauera played pivotal roles on N removal in TFCWs. Furthermore, better gradient oxic environments by 8 h-HRT promoted co-occurrence of heterotrophic nitrifiers (mostly Pseudomonas stutzeri) and autotrophic nitrifiers (mostly Nitrosomonas europaea. and Nitrospira sp.) which potentially accelerated NH4+-N oxidation by elevated nitrification and denitrification related genes. Meanwhile, the addition of HN-AD bacteria stimulated nirA and gltD genes of N assimilation processes probably leading to NH4+-N directly removal in TFCWs. The conceptual model of microbial N and P transformation in TFCWs highlighted the importance of glycolysis pathway which were vital drivers to nutrients metabolism.