Microbial electrochemical cells (MXCs) using cation and anion exchange membranes (CEM and AEM) were tested in batch mode for ammonium recovery. Experimental results showed superior ammonium recovery of 61% in CEM-MXC. Migration effect accounted for 61% of the total ammonium recovery in CEM-MXC where other ammonium ions (39%) were transferred by diffusion. Current density was significant for improving the recovery rate of ammonium nitrogen, but proton accumulation deteriorated current density in CEM-MXC. The dissolution of ammonia hydrolyzed by urea produces hydroxyl ions, which can neutralize protons in the anode and maintain high current density in CEM-MXC. However, anodic pH increased over 9 at high current density (>2 A/m(2)) in CEM-MXC fed by urea, which indicates that the rate of ammonia dissolution becomes faster than proton accumulation rate at high current density. Balancing proton-accumulating rate with ammonia dissolution rate in the anode is significant for improving ammonium recovery in CEM-MXC. (C) 2013 Elsevier Ltd. All rights reserved.