Bio-hydrogen production and wastewater treatment are two processes that take place simultaneously within microbial electrolysis cells (MEC). Therefore, in this study, MEC1 (300ml), MEC2 (400ml) and MEC 3 (500ml) were used as three different volumes to produce bio-hydrogen, and the ability of each of them to treat wastewater was evaluated. Also, three different types of bacterial strains (Escherichia coli NRRL B-3008, Enterobacter aerogenes DSM 30053 and Pseudomonas aeruginosa ATCC 27853) were used to catalyze the anode reactions in the MEC. The applied voltage was used to operate MEC is 0.4, 0.6 and 0.8 V. The wastewater was intended for treatment is domestic wastewater and industrial wastewater. The results were based on estimating the values of Bio-hydrogen production rates (Bio-HPR), hydrogen yield (YH2 %), and Chemical oxygen demand (COD) removal efficiency (%). In MEC 3 (500 ml) at applied voltage 0.8 V and industrial wastewater was gave the highest rates of values for Bio-HPR 358.24cm3, YH2 93.64% and COD removal efficiency 88.04% were obtained by Escherichia coli NRRL B-3008. The lowest values were obtained from MEC1 (300 ml) at applied voltage 0.4 V were Bio-HPR 41.49 cm3, YH2 16.15 % and COD removal efficiency 67.07% by domestic wastewater without bacteria.