An intensified biofilm-electrode reactor (IBER) was developed to treat nitrate-contaminated drinking water. Different running conditions were conducted to investigate the behavior of autotrophic denitrification (AD) and heterotrophic denitrification (HD) in the IBER. In AD process, the nitrate nitrogen coulomb-reduction rate was used to evaluate the performance of the reactor. The maximum NO3--N removal efficiency was 6.8% at the current of 60 mA, while nitrate nitrogen coulomb-reduction rate was 0.024 mgC(-1). The optimum conditions for HD process were C/N = 0.8 and HRT = 8 h, under which complete NO3--N removal and no NO2--N accumulation were observed. With the cooperative effect of AD and HD in the heterotrophic and autotrophic denitrification (HAD) process, large treatment capacity, high denitrification efficiency, and low nitrite and ammonia accumulation were achieved. The results proved that HAD process was superior to single AD and HD for nitrate removal in the IBER. (C) 2011 Elsevier Ltd. All rights reserved.