Biohydrogen: Chapter 7. Photofermentative Biohydrogen Production

There are many biological paths to hydrogen production, each with potential advantages, but also with its own challenges to implementation. Nonsulfur photosynthetic bacteria are able to capture solar energy and use it to drive the nearly complete conversion of substrate to hydrogen and carbon dioxide in a process called photofermentation. These organisms, which have the potential capacity to use a variety of feedstocks, are well known for their light-driven conversion of organic acids to hydrogen and carbon dioxide. Thus, they are ideal candidates for two-stage or coculture systems that derive additional hydrogen from the effluents of dark fermentations. In addition, various industrial and agricultural waste streams rich in organic acids can potentially serve as substrates for photofermentation. The metabolic and enzymatic properties underlying photofermentation, as well as possible waste streams that may be used successfully, are reviewed. Recent progress, including the use of immobilized systems and metabolic engineering, is highlighted.