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

•A simple continuous fermentation system (CFS) was developed.•CFS was efficient for continuous synergistic dark and photo-fermentation H2 production.•CFS was used efficiently for synergistic hydrogen and ABE production by continuous dark fermentation.•The system was also efficient for continuous H2 and methane production.

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 H2 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 H2 production by Clostridium acetobutylicum and Rhodobacter capsulatus producing 5.65 mole H2 mole− 1 hexose; (2) Continuous dark-fermentation synergistic H2, acetone, butanol and ethanol (ABE) production by C. acetobutylicum which produced per mole hexose, 2.43 mol H2 along with 73.08 g ABE (3) Continuous H2 and methane production by C. acetobutylicum and bacterial sludge producing, per mole hexose, 1.64 mol pure H2 and 2.56 mol CH4 mixed with 0.37 mol H2·The hydraulic retention time (HRT) for whole system was short where organic acids produced in dark-fermentation in first fermenter were synergistically utilized for H2 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.

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