Photobiological hydrogen production using a new plate loop reactor

The photobiological production of hydrogen has been discussed as a possibility of solar energy conversion. This approach, however, seems to be economical only when a cheap and effective fermentation technology is available. A plate loop reactor was designed for photobiological processes with immobilized cells. The liquid flow was driven by the hydrogen bubbles and the thermal effects in the reactor, so that no external energy was needed for stirring. The maximum hydrogen production with suspended Rhodobacter capsulatus-cells in the sun was 2 l/h . m(2). The dependency of microbial growth and hydrogen evolution on different light qualities was examined. Rhodobacter capsulatus was sensitive against light of short frequencies, especially with glucose as a substrate. The cells were able to switch from photo metabolism to other metabolic pathways and produce formate, acetic acid and other organic acids. The decreasing pH led to cell damage. This problem can be diminished by using diverse filters. There was no reduction of hydrogen production even when all frequencies < 550 nm were eliminated. For concentrating the active biomass in the reactor and for exposing the cells to the light on an equal layer, the cells were immobilised as a biofilm on different surfaces. The biofilm dry weight depended on light intensity, and increased up to 2,64 mg/cm(2) at 180 W/m(2). The ATP-content in the film-fixed organisms was found to be five times higher than in the suspended organisms.