Biohydrogen production from dairy wastewater with subsequent biogas purification by hollow fiber membrane module was investigated in this study. The purified and not purified (raw) biohydrogen were used as fuel in polymer electrolyte membrane (PEM) fuel cell. Furthermore, the effect of CO2 on the performance of PEM fuel cell was evaluated considering cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and polarization curves. The maximum H-2 production rate was 0.015 mmol H-2/mol glucose and the biohydrogen concentration in biogas was ranged 33%-60% (v/v). CO2/H-2 selectivity decreased with increasing pressure and maximum selectivity was obtained as 4.4 at feed pressure of 1.5 bar. The electrochemical active surface (EASA) areas were decreased with increasing CO2 ratio. The maximum power densities were 0.2, 0.08 and 0.045 W cm(2) for 100%, 80% and 60% (v/v) H-2, respectively. The results indicated that integrated PEM fuel cell/biogas purification system can be used as a potential clean energy sources during acidogenic biohydrogen production from dairy wastewater. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.