Simultaneous enhancement of organics and nitrogen removal in drinking water biofilm pretreatment system with reed addition

► Nitrate removal efficiency was positively related with the influent C/N ratio. ► Nitrogen removal was enhanced via reed addition in drinking water biofilm pretreatment system. ► Combined with HRT regulation, low effluent nitrate and TOC concentrations were achieved. ► Bacteria diversity shifted significantly with the variation of the influent C/N ratio.