A new approach was developed to achieve autotrophic nitrogen removal from ammonium at low applied voltage in a single-compartment 3-dimensional microbial electrolysis cell (MEC). The MEC consisted of anodic and cathodic electrodes, on which nitrifying and denitrifying biofilms, respectively, were attached. Nitrogen removal can be enhanced at an applied voltage in the MEC. Besides, the nitrogen removal efficiency gradually increased from 70.3% to 92.6% with the increase of applied voltage from 0.2 to 0.4 V, as well as the maximum current was varied from 4.4 to 14 mA. The corresponding coulombic efficiency also increased from 82% to 94.4%, indicating that the increasing applied voltage could enhance electron extraction from ammonium during its oxidative removal. The DO was found to be a critical factor which affected the nitrogen removal in this MEC system. These results demonstrated that the MEC process was applicable to achieve autotrophic nitrogen removal from wastewater containing ammonium. (C) 2012 Elsevier Ltd. All rights reserved.