Microbial electrolysis cells (MECs) are potential candidates for sustainable wastewater treatment as they allow for recovery of the energy input by producing valuable chemicals such as hydrogen gas. Evaluating the effectiveness of MEC treatment for different waste-waters requires new approaches to quantify performance, and the establishment of specific procedures and parameters to characterize the outcome of fed-batch treatability tests. It is shown here that Coulombic efficiency can be used to directly calculate energy consumption relative to wastewater treatment in terms of COD removal, and that the average current, not maximum current, is a better metric to evaluate the rate of the bioelectrochemical reactions. The utility of these methods was demonstrated using simulated current profiles and actual wastewater tests. Industrial and domestic wastewaters were evaluated using small volume MECs, and different inoculation strategies. The energy needed for treatment was 2.17 kW h kg(COD)(-1) for industrial wastewater and 2.59 kW h kg(COD)(-1) for domestic wastewater. When these wastewaters were combined in equal amounts, the energy required was reduced to 0.63 kWh kg(COD)(-1). Acclimation of the MEC to domestic wastewater, prior to tests with industrial wastewaters, was the easiest and most direct method to optimize MEC performance for industrial wastewater treatment. A pre-acclimated MEC accomplished the same removal (1847 +/- 53 mg L-1) as reactor acclimated to only the industrial wastewater (1839 +/- 57 mg L-1), but treatment was achieved in significantly less time (70 h versus 238 h). Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.