A novel drinking water biofilm pretreatment process with reed addition was established for enhancement of simultaneously organics and nitrogen removal. Results showed that nitrate removal efficiency was positively related with the influent C/N ratio, reaching to 87.8 +/- 2.8% at the C/N ratio of 4.7. However, the predicted trichloromethane (THM) levels based on total organic carbon (TOC) and UV254 were high with the increase of influent C/N ratio. Combined with the pollutants removal performance and microbial community variation, an appropriate C/N ratio via reed addition was determined at 2.2 for the continuous biofilm reactor. With adjustment of hydraulic retention time (HRT), the highest of nitrate removal efficiency (74.2 +/- 1.4%) and organics utilization efficiency (0.63 mg NO3--N mg(-1) TOC) were achieved at an optimum HRT of 18h, with both low effluent NO3--N (0.88 +/- 0.03 mgl(-1)) and TOC (2.86 +/- 0.67 mgl(-1)). (C) 2012 Elsevier Ltd. All rights reserved.