Photobiological hydrogen production: photochemical efficiency and bioreactor design

Biological production of hydrogen can be carried out by photoautotrophic or photoheterotrophic organisms. Here, the photosystems of both processes are described.The main drawback of the photoautotrophic hydrogen production process is oxygen inhibition. The few efficiencies reported on the conversion of light energy into hydrogen energy are low, less than 1.5% on a solar spectrum basis. However, these can be increased to 3–10%, by the immediate removal of produced oxygen.The photochemical efficiency of hydrogen production can be calculated theoretically, and is estimated to be 10% (on solar spectrum basis) for the photoheterotrophic process. With use of the theoretical photochemical efficiency, and the climatic data on sunlight irradiance at a certain location at a certain moment of the year, the theoretical maximum hydrogen production can be estimated.Data on H₂ yields and photochemical efficiency from experiments reported in the literature are summarized. Photochemical efficiencies, essentially based on artificial light, can reach 10% or even more, but only at low light intensities, with associated low-H₂ production rates.Some reflections on possible photobioreactors lead to two types of (modified) photobioreactors that might be successful for a large-scale biological hydrogen production.