Effects of hydrogen partial pressure on fermentative biohydrogen production by a chemotropic Clostridium bacterium in a new horizontal rotating cylinder reactor.

peer reviewedHydrogen is widely considered as the most promising energetic carrier. At an industrial scale, steam reforming of methane is currently the major hydrogen producing process. But it may also be produced from renewable biomass. Indeed, the fermentative production of hydrogen from renewable biomass using anaerobic bacteria could at least partially reduce our dependence on fossil fuel, decrease the carbon dioxide emissions and produce “green” energy. It offers the potential production of usable hydrogen from a variety of renewable resources such as carbohydrates wastes from agriculture or agro-food industries. This technology is based on anaerobic fermentation, called dark fermentation, by chemotrophic bacteria. The investigations carried out at CWBI involve selection and characterization of bacteria strains able to produce biohydrogen efficiently and with a wide range of substrate. The selected strains at the laboratory has been characterised as Clostridium sp. In order to produce hydrogen at high yields and production rates, the biotechnological process needs to be further optimized and efficient bioreactors must be designed. At CWBI, a new reactor called “horizontal rotating cylinder bioreactor” allows the production of biohydrogen from glucose with our Clostridium sp. strain with a high yield and production rate. This reactor, working continuously, has an internal volume of 2.3l but a working volume (liquid phase) of 300ml. Firstly, it enhances the hydrogen production rate by partially fixing the bacteria on the porous cylinder and thus increasing the cell concentration in the bioreactor. Secondly, the rotative cylinder enables efficient gas transfer (mainly hydrogen) from the liquid phase where it is produced by the bacteria. This is an important way to enhance hydrogen production yield by allowing the bacteria metabolism to shift in a fermentation type that produces more hydrogen. This was confirmed by increasing or decreasing the total pressure in the bioreactor and observing the influence of hydrogen production. The liquid to gas hydrogen transfer is possibly an important factor to enhance the biogas production. Our investigation confirmed this by testing different liquid to gas transfer condition in BHP test (batch fermentation in 250ml serum bottles).This was made either by decreasing total and partial pressure or by increasing the mixing state of the media. Our work concludes the importance of providing good liquid to gas transfers in the biohydrogen producing reactors to enhance the hydrogen production and reach higher yields and production rates.MicroH