Dark-fermentation

In conclusion, the rates and efficiencies of hydrogen production by systems directly using photosynthesis fall short of even plausible economic feasibility. Since organic substrates are the ultimate source of hydrogen in photofermentations or indirect biophotolysis processes, it can be argued that it should be simpler and more efficient to extract the hydrogen from substrates using a dark fermentation process, an approach which is discussed next. 

Dark fermentation is the fermentative conversion of organic substrate to biohydrogen, it is a complex process manifested by a diverse group of bacteria by a series of biochemical reactions involving three steps similar to anaerobic conversion. Dark fermentation differs from photofermentation because it proceeds without the presence of light. 

Koskinen, P.E.P., Kaksonen, A.H., Puhakka, J.A. 2007. The relationship between instability of Hj production and compositions of bacterial communities within a dark fermentation fluidized-bed bioreactor. Biotechnol Bioeng 97 742-758. 

Bioprocesses for hydrogen production are in an early stage of development. Processes are usually split in those requiring incident sunlight (bio-photolysis and photo-fermentation) and those that can be carried out in the absence of light (dark fermentations). 

Dark fermentation is a catabolism anaerobic bacteria convert sugars and proteins to carboxylic acids, hydrogen, carbon dioxide, and solvents. This biological chemical reaction is carried out under anaerobic condition in which the presence of oxygen is prohibited. 

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