The present study examines the effect of the organic loading rate and the configuration of a semi-pilot modular microbial electrolysis cell (MEC) on the energy consumption during domestic (dWW) wastewater treatment. The MEC reactor consisted of twin tubular units hydraulically connected in series and was able to reduce up to 85% of the chemical oxygen demand (COD) concentration of the influent dWW at a relatively low energy consumption (1.6 kW h kg-COD(-1)). Hydrogen production was limited by the reduced amounts of organic matter fed into the reactor and the poor performance of the cathode. Overall, the results identified both an organic loading rate (OLR) threshold that makes the use of MECs for dWW treatment feasible in terms of energy consumption and COD removal efficiency and an OLR threshold that justifies the operation of two MECs in series to provide the required degree of COD removal.