Methanogenic bioreactors, which are packed with supporting material, have attracted attention as an efficient means of degrading garbage. We aimed to increase bioreactor performance by using an electrochemical system to regulate the electrical potential on supporting material. At an organic loading rate of 26.9 g dichromate chemical oxygen demand (CODcr)/L/day, reactors with a potential of -0.6 or -0.8 V, generated by a cathodic electrochemical reaction, showed greater removal of CODcr and methanogenesis than reactors with a potential of 0.0 or -0.3 V, generated by anodic reaction, or control reactors without electrochemical regulation. 16S rRNA gene analysis revealed that the same methanogens were present in all our reactors, but quantitative real-time polymerase chain reaction showed that higher prokaryotic and methanogenic copy numbers were present on cathodic electrodes than on anodic or control electrodes. These results indicate that cathodic electrochemical regulation can support methane fermentation from garbage. (C) 2009 Elsevier Ltd. All rights reserved.