The present investigation deals with Rhodopseudomonas palustris sp. grown, using acetate, for purposes of hydrogen generation. All experiments were carried out using a lab-scale photobioreactor. The cultures were irradiated with a 150W(OSRAM power star HQI-TS) lamp impinging on the reactor surface an irradiance of 74 W/m(2). Three different growth regimens were compared: batch, fed-batch, and semi-continuous. In the third approach, two daily dilutions were applied, in order to operate the photobioreactor at two hydraulic retention times: 240 h in the first semi-continuous regimen (SC240h) and 60 h in the second (SC60h). The best performances were attained when operating the photobioreactor in fed-batch mode. A maximum hydrogen production rate of 15.21 mL(H-2)/L h was achieved. The hydrogen yield (Y-H) was 1.60 mol H-2/mol acetic acid in SC240h; 1.42 mol H-2/mol acetic acid when the culture was operated in fed-batch mode, and 0.85 mol H-2/mol acetic acid under a batch growth regimen. YH decreased to 0.36 mol H-2/mol acetic acid in SC60h. Significant changes in the oxidation-reduction potential were noted among the selected growth regimens tested then and also over time. (C) 2015 Elsevier Ltd. All rights reserved.