The effect of pH on cooperation between dark-and photo-fermentative bacteria in a co-culture process for hydrogen production from starch

The effect of pH control in biohydrogen production from starch by co-culture of dark fermentative Clostridium acetobutylicum and photofermentative Rhodobacter sphaeroides bacteria was studied. It was compared with hydrogen production rate and H-2 yield obtained for single culture photo and dark fermentation. Development of stable bacteria co culture resulted in complete decomposition of starch without accumulation of volatile fatty acids. Moreover, the amount of produced hydrogen was 2.5 fold higher than for single dark fermentation process, where maximum H-2 production reached 0.939 L H-2/L-medium at pH 5.5. Acclimatization of C. acetobutylicum to starch and control of pH at 7.0 was found optimum for bacteria cooperation in the co-culture, resulting in simultaneous H-2 production by both bacteria species. Cumulative H-2 production and H-2 yield in this process reached 2.29 L H-2/L-medium and 5.11 mol H-2/mol(oucos)e, respectively. Higher amounts of hydrogen (2.67 L H-2/L-medium) were obtained in a co-culture process in which pH was raised from 6.0 to 7.5 after dark fermentation stage. However, under these conditions dark and photofermentation stages were separated in time. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.