Performance and bacterial communities in unsaturated and saturated zones of a vertical-flow constructed wetland with continuous-feed.

• Sufficient removal of pollutants was achieved despite the temperature varied. • Removal of COD, NH 4 +-N, TIN and TP mainly occurred within the unsaturated zone. • Microbial community exhibited great succession with season as well as depth. • Unsaturated zone benefited the enrichment of functional group for nutrient removal. • Diverse mechanism of nitrogen removal existed in VFCW while varied along the depth. In this study, a partially-saturated vertical-flow constructed wetland (VFCW) with continuous-feed was operated to investigate nutrients transformation and possible pathways in unsaturated and saturated zones. Effect of temperature on nutrients removal and microbial community was also evaluated. The variation of temperature barely affected removal of NH 4 +-N and COD, achieving removal efficiencies of 99.5–100.0% and 96.8–100.0% at effluent temperature of 14.9–27.7 °C. The removal of COD, NH 4 +-N, total inorganic nitrogen (TIN) and total phosphorus mainly occurred in unsaturated zone, achieving much higher removal rates than saturated zone. Nitrification process in the VFCW was associated with autotrophic/heterotrophic ammonia oxidizing bacteria and nitrite oxidizing bacteria. Denitrification process relied on both autotrophic and heterotrophic denitrifiers. Anaerobic ammonium oxidizing bacteria was also detected, contributing to TIN removal. All of the groups for nutrients removal exhibited higher abundance in unsaturated zone. Diverse pathways co-existed for nitrogen removal, while the main metabolic pathways were different along the depth. [ABSTRACT FROM AUTHOR]