Intensified nitrogen removal by heterotrophic nitrification aerobic denitrification bacteria in two pilot-scale tidal flow constructed wetlands: Influence of influent C/N ratios and tidal strategies

[Display omitted] •High C/N ratios and effluent recirculation promoted SND process for N removal.•HNAD was the main nitrogen transformation pathway in TFCWs.•HNADB were the dominant functional genera related to nitrogen removal in TFCWs.•Some core HNADB showed positive interactions with other functional genera.•Tidal strategies contributed more to shifts in functional genera than C/N ratios. This study investigated the influence of C/N ratios and tidal strategies on nitrogen removal and bacterial communities in two pilot-scale tidal flow constructed wetlands (TFCWs) with simultaneous nitrification–denitrification process. Heterotrophic nitrification aerobic denitrification (HNAD) was the main nitrogen transformation pathway in both TFCWs. High C/N ratios and effluent circulation at low temperature promoted HNAD in TFCWs with high nitrogen removal efficiencies (72.6%–95.5% for NH4+-N and 70.9%~91.8% for TN). Effluent circulation had more influence on bacterial community structure and diversity than C/N ratios. Among 16 detected genera related to nitrogen removal, HNAD bacteria (HNADB) were abundant. Especially, some dominant HNADB (e.g. Aeromonas, Hydrogenophage and Gemmobacter) were core genera, showing positive interactions with other genera related to nitrogen removal. Tidal strategies had more contribution to the shifts in these genera than C/N ratios. This study highlights the importance of HNADB in pilot-scale TFCWs and their responses to C/N ratios and tidal strategies.