The microbial electrolysis process allows producing hydrogen (H-2) as a result of the cathodic reaction of the protons coming from the oxidation of the organic matter contained in waste water. For the application of this technology it is necessary to study the optimal operating conditions that allow to scale-up a microbial electrolysis cell to produce hydrogen efficiently at low cost. This study used a new approach to get high hydrogen production rate in a MEC by achieving in a very short time the process for making the anode's bacteria enrichment for the biofilm formation. The hydrogen production efficiency was optimized through the change of the electrolyte conductivity and the electrode surface area/electrolyte volume ratio. It was found that the hydrogen production rate increased with the increase of the electrolyte conductivity. Its rate (Q(H2)) increased from 0.13 to 0.82 m(3)H(2)/m(3) per day when the electrolyte conductivity increased from 7.5 mS/cm to 15 mS/cm. From the optimization of the electrolyte conductivity and the electrode surface area/electrolyte volume ratio, the highest cathodic reaction efficiency of 97% and coulombic efficiency of 21% were obtained. These results show for the first time that the improvement of the electrodes bacteria enrichment process at the anode is an important approach to enhance the hydrogen production rate in a MEC. The results in this study were verified by repeating the experiments more than once and comparing our results with similar studies already published in the literature. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.