Fermentative hydrogen and methane production from microalgal biomass (Chlorella vulgaris) in a two-stage combined process

This study investigated the hydrogen fermentation in a two-stage combined fermentation process (combination of dark fermentation for hydrogen (H2) production from microalgae and methane (CH4) fermentation from residues following H2 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 H2 g-VS−1 at different substrate dosages without enzymatic pre-treatment. A seven-fold increase in H2 production yields (19 ± 2.94–135 ± 3.11 ml H2 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.