The prospect of purple non-sulfur (PNS) photosynthetic bacteria for hydrogen production: The present state of the art

Hydrogen is the fuel for the future, mainly due to its recyclability and nonpolluting nature. Biological hydrogen production processes are operated at ambient temperature and atmospheric pressures, thus are less energy intensive and more environmentally friendly as compared to thermochemical and electrochemical processes. Biohydrogen processes can be broadly classified as: photofermentation and dark fermentation. Two enzymes namely, nitrogenase and hydrogenase play an important role in biohydrogen production. Photofermentation by Purple Non-Sulfur bacteria (PNS) is a major field of research through which the overall yield for biological hydrogen production can be improved significantly by optimization of growth conditions and immobilization of active cells. The purpose of this paper is to review various processes of biohydrogen production using PNS bacteria along with several current developments. However, suitable process parameters such as carbon and nitrogen ratio, illumination intensity, bioreactor configuration and inoculum age may lead to higher yields of hydrogen generation using PNS bacteria.