This study investigated the hydrogen fermentation in a two-stage combined fermentation process (combination of dark fermentation for hydrogen (H-2) production from microalgae and methane (CH4) fermentation from residues following H-2 production process). Microalgae Chlorella vulgaris culture was used as a substrate. The hydrogen production from C vulgaris ranges 1.75 +/- 1.50-19 +/- 2.94 ml H-2 g-VS-1 at different substrate dosages without enzymatic pre-treatment. A seven-fold increase in H-2 production yields (19 +/- 2.94-135 +/- 3.11 ml H-2 g-VS-1) was observed with enzymatic pre-treatment (Onozuka R-10 and Macerozyme R-10) of the microalgae. The results of the CH4 fermentation show that the methane yields could be increased from 245 +/- 2.46 to 414 +/- 2.45 ml CH4 g-VS-1 by using enzymatic pretreatment. In addition, the yield of the CH4 fermentation (14.86 kJ/g-VS) has approximately the same order of magnitude in comparison to the two-stage combined fermentation process (14.46 kJ/g-VS) in terms of energy production. (C) 2014 Elsevier Ltd. All rights reserved.