5. 4. 1 What is hydrogen fermentation?

Anaerobic fermentation is a reaction in which anaerobic microorganisms oxidatively decompose organic materials to get energy under anaerobic conditions. We call fermentative reactions in which hydrogen is the final product as hydrogen fermentation. In hydrogen fermentation, some organic materials and alcohols are produced with hydrogen. Although final electron acceptor is oxygen or inorganic materials in respiration, oxidatively degraded organic materials and carbon dioxide etc. from substrate materials are final products in fermentation. For example, final products are ethanol and carbon dioxide from glucose during ethanol fermentation. While ATP synthesis is coupled with electron transfer chain in respiration, ATP is produced in reactions at substrate level in fermentation. Energy gained from fermentation is smaller than that from respiration for the same amount of substrate.

5.4.2 Characteristics of hydrogen fermentation

The role of hydrogen production is to regulate oxidation-reduction level in bacterial cells by converting excess reducing power to hydrogen. There are bacteria which can take in and utilize such hydrogen. In order to increase hydrogen yields, the reverse reactions consuming hydrogen should be suppressed. Generally, it is needed to treat waste water from hydrogen fermentation, since hydrogen fermentation includes the production of some organic materials.