Photofermentative molecular biohydrogen production by purple-non-sulfur (PNS) bacteria in various modes: The present progress and future perspective

• This review covers photofermentative H2 production by purple-non-sulfur bacteria only.
• Dark fermentative & photobiological H2 production is outside the scope of this review.
• Photofermentative H2 production in various mode: batch, fed-batch & continuous operation.
• Photobioreactor designing & light conversion efficiency key points for lower cost.
• Immobilized-cell PBR increases cell concentration & H2 production rate.

Hydrogen is green fuel for the future, mainly due to its recyclability. Biohydrogen production processes are less energy intensive and environmental friendly in compared to chemical processes. Fermentative biohydrogen production can be broadly classified as: dark and photo fermentation. Two enzymes, nitrogenase and hydrogenase play important role in biohydrogen production. Purple Non-Sulfur bacteria (PNS) are mainly used in photofermentative hydrogen production through which the overall yield can be improved manifolds. The scope and objective of this review paper is to investigate the performance of various light driven photofermentative hydrogen production by PNS bacteria along with several developmental works related to batch, repeated batch, feed batch and continuous operation. However the study of Photobiological process by microalgae or cyanobacteria is outside the scope of this review. Optimization of suitable process parameters such as carbon and nitrogen ratio, illumination intensity, bioreactor configuration, immobilization of active cells in specific continuous mode and inoculum age may lead to higher yield of hydrogen generation.