Photofermentation

Photofermentation is the fermentative conversion of organic substrate to biohydrogen manifested by a diverse group of photosynthetic bacteria by a series of biochemical reactions involving three steps similar to anaerobic conversion.

For example, photo-fermentation with Rhodobacter sphaeroides SH2C (or many other purple non-sulfur bacteria[1]) can be employed to convert small molecular fatty acids into hydrogen[2] and other products.

[4] Photolytic producers are similar to phototrophs, but source hydrogen from water molecules that are broken down as the organism interacts with light.

[6][7] Photofermentation via algae instead of bacteria is used for bioethanol production, among other liquid fuel alternatives.

[8] The bacteria and their energy source are held in a bioreactor chamber that is impermeable to air and oxygen free.

[7] The bacteria are sustained with a carbohydrate diet consisting of simple saccharide molecules.

[5] Other explorations include expanding the bioreactor system to hold a combination of bacteria, algae or cyanobacteria.

[7][9] Ethanol production is performed by the algae Chlamydomonas reinhardtii, among other species, in cycling light and dark environments.

[10] The bacteria are typically fed with broken down agricultural waste or undesired crops, such as water lettuce or sugar beet molasses.

[12] The primary limitations of photofermentation as a sustainable energy source stem from the precise requirements of maintaining the bacteria in the bioreactor.

[7] Researchers have found it difficult to maintain a constant temperature for the bacteria within the bioreactor.