Requirement of NOi presence in feed is one barrier of anammox process for the application since NOi is not a frequent composition in most wastewaters. In this study, anodic oxidation of NH4+ to NO2- was realized in a single-chamber bioelectrochemical system with an anodic potential of-0.5 V. The NO2- product compensated its lack in the feed to accelerate the anammox. As a result, the anammox efficiency increased by at least 29.2%. When the potential was removed, the nitrogen removal in these two reactors had no significant differences. The SEM images and FISH analysis suggested that the abundance of anammox bacteria was obviously higher in R2. (C) 2016 Elsevier B.V. All rights reserved.