Synergistic dark and photo-fermentation continuous system for hydrogen production from molasses by Clostridium acetobutylicum ATCC 824 and Rhodobacter capsulatus DSM 1710.

This study investigated synergistic dark and photo-fermentation using continuous fermentation system (CFS). The system relies on connecting several fermenters from bottom of one to top culture level of the next in a manner that allows for delaying movement of the substrate and thus for its full consumption. While H was collected, CFS allowed for moving liquid byproducts toward the outlet and hence continuous productivity. CFS could be efficiently used for: (1) Continuous dark and photo-fermentation H production by Clostridium acetobutylicum and Rhodobacter capsulatus producing 5.65moleHmole hexose; (2) Continuous dark-fermentation synergistic H, acetone, butanol and ethanol (ABE) production by C. acetobutylicum which produced per mole hexose, 2.43mol H along with 73.08g ABE (3) Continuous H and methane production by C. acetobutylicum and bacterial sludge producing, per mole hexose, 1.64mol pure H and 2.56mol CH mixed with 0.37mol H·The hydraulic retention time (HRT) for whole system was short where organic acids produced in dark-fermentation in first fermenter were synergistically utilized for H production by R. capsulatus in subsequent fermenters. CFS is suitable for fast-digestible sugars but not lignocelluloses or other hard-digestible organics, requiring prolonged HRT, unless such polymeric organics were hydrolyzed prior to fermentation.