Optimization of Batch Dark Fermentation of Chlorella sp. Using Mixed-Cultures for Simultaneous Hydrogen and Butyric Acid Production

This paper reports on the optimum conditions for simultaneous hydrogen and butyric acid production from microalgae (Chlorella sp.) using enriched anaerobic mixed cultures as inoculum. The fermentation was objectively carried out under acidogenic conditions to achieve butyric acid for further ABE fermentation in solventogenesis stage. The main effects of initial pH (5 and 7), temperature (35 degrees C and 55 degrees C), and substrate concentration (40, 60, 80, and 100 g-VS/L) for hydrogen and butyric acid production were evaluated by using batch fermentation experiment. The major effects on hydrogen and butyric acid production are pH and temperature. The highest production of hydrogen and butyric acid was observed at pH 7 and temperature 35 degrees C. Using initial Chlorella sp. concentration of 80 g-VS/L or 100 g-VS/L at pH 7 and temperature 35 degrees C could produce hydrogen with an average yield of 22 mL-H-2/g-VS along with high butyric acid production yield of 0.05 g/g-VS, suggesting that microalgae (Chlorella sp.) has potential to be converted directly to butyric acid by using acidogenesis under above optimum conditions.