Microbial electrolysis represents a new approach for harnessing the energy contained in the organic matter of wastewater. However, before this approach can be implemented on a practical basis, a cost-effective manufacturing process for microbial electrolysis cells (MECs) must be developed. The objective of this study is to estimate an acceptable purchase cost of an MEC reactor for a domestic wastewater treatment plant. We estimate that for a full-scale MEC operating at a current density of 5 A m(a)(-2) (amperes per square meter of anode) and an energy consumption of 0.9 kWh kg-COD-1 (kilowatt-hour per kg of removed chemical oxygen demand (COD)), a cost of (sic)1220 m(a)(-3) (euro per m(3) of anodic chamber) can be established as a target purchase cost at which a break-even point is reached after 7 years. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.