Perspectives on cultivation strategies and photobioreactor designs for photo-fermentative hydrogen production

Photosynthetic bacteria have considerable biotechnological potential for biological hydrogen production due to higher substrate conversion efficiency and hydrogen yield. Phototrophic fermentation using photosynthetic bacteria has a major advantage of being able to further convert the byproducts originating from dark fermentation (e.g., volatile fatty acids) to hydrogen. Through the combination of dark and photo-fermentation processes, organic feedstock is fully converted into gaseous product (H2) at the highest possible H2 yield, with significant reduction of chemical oxygen demand (COD). The performance of photo-fermentation is highly dependent on the medium composition, culture conditions, and photobioreactor design. Therefore, this article provides a critical review of the effects of key factors affecting the photo-hydrogen production efficiency of photosynthetic bacteria, and also summarizes the strategies being applied in promoting the performance of photo-fermentation.