Surface modifications of electrode materials are important for improved performance of microbial bio-electrochemical systems. Here, we studied the effect of pre-treating both glassy carbon and graphite felt electrodes with either an oxygen or a nitrogen plasma before reactor inoculation with a mixed microbial consortia. The plasma produces chemical modifications at the electrode surface level. X-ray photoelectron spectroscopy and water contact angle analysis showed that the plasma removes surface contamination, produces ion implantation and renders the hydrophobic surfaces highly hydrophilic. Plasma pre-treatment considerably accelerated the generation of a bio-electrochemical anodic current after inoculation. Nitrogen plasma pre-treatment yielded the best performance, followed closely by oxygen plasma. Plasma pre-treated electrodes reached a plateau of maximum current density twice as fast as untreated electrodes. Analysis of the current development profiles suggests that the plasma pretreatment is neither producing a preferential attachment of certain types of bacteria over others nor accelerating the extracellular electron transfer rate. The results indicate that the plasma treatment considerably enhances the initial cell adhesion, which results in subsequently faster biofilm development. Plasma pre-treatment of electrodes is an inexpensive, fast, safe and straightforward technique to achieve more rapid start-up of bio-electrochemical processes. (C) 2013 Elsevier Ltd. All rights reserved.