Hydrogen generation in a pressurized photobioreactor: Unexpected enhancement of biohydrogen production by the phototrophic bacterium Rhodobacter capsulatus

Environmental concerns are generating a growing interest of the hydrogen sources, however hydrogen exhibits critical storage barriers. The production of pressurized biohydrogen would facilitate the gas storage and make it economically viable. In this work, Rhodobacter capsulatus in a closed photosynthetic reactor exhibited the ability to produce hydrogen to a pressure of 8.25 bars. The amount of hydrogen produced from synthetic media (lactate (35 mmol L-1) and glutamate (5 mmol L-1)) in a closed vessel was 1.8 times that obtained in a vessel open to the atmosphere. Hydrogen purity surpassed 90% with a lactate conversion rate of up to 70%. Influences of buffer composition in synthetic media and the illumination process (white LED or Na-lamp) are discussed. Moreover, pressurized hydrogen was successfully produced from a complex real effluent containing organic acids (lactate and acetate) generated by an initial dark biofermentation of hydrolyzed wheat straw. Therefore, under pressurized conditions, the stress increases the energetic demand and improves hydrogen production (survival vs growth). The energetic gain of the direct compression of biohydrogen d is equal to 1.3 kWh/kg H-2.