Photofermentative hydrogen production from wastes

In many respects, hydrogen is an ideal biofuel. However, practical, sustainable means of its production are presently lacking. Here we review recent efforts to apply the capacity of photosynthetic bacteria to capture solar energy and use it to drive the nearly complete conversion of substrates to hydrogen and carbon dioxide. This process, called photofermentation, has the potential capacity to use a variety of feedstocks, including the effluents of dark fermentations, leading to the development of various configurations of two-stage systems, or various industrial and agricultural waste streams rich in sugars or organic acids. The metabolic and enzymatic properties of this system are presented and the possible waste streams that might be successfully used are discussed. Recently, various immobilized systems have been developed and their advantages and disadvantages are examined.

► Photofermentation can potentially produce hydrogen from a variety of feedstocks.
► Industrial and agricultural wastes rich in sugars can be treated in two stage systems.
► Organic acids and the effluents of dark fermentations are possible substrates.
► Immobilized systems are under development and may have some advantages.