2.7　Hydrogen-producing Acetogenic Bacteria in Aqua of Biogas Fermentation

2.7.1　Hydrogen-Producing Acetogenic Bacteria in Biogas Fermentation Liquid

Apart from acetic acid, CO2and H2in the products of anaerobic fermentation of carbohydrate, lipids and protein, can be directly utilized by methane-producing bacteria. The rest, such as alcohol, volatile saturated organics, including butyric acid and propanic acid, can neither be used directly by methane producing bacteria, nor be served as resourses of energy and carbon unless they are further converted into acetic acid, CO2and H2.This group of bacteria, therefore, is of extreme importance in the colony of non-methane-producing microbes.

From 1980 to 1982, a study of hydrogen-producing microbes in biogas digester was performed by Chengdu Institute of Biology, Chengdu Branch of Chinese Academy of Science and the result showed that when adding Chinese yam to the abstracting media of biogas sludges, the production of hydrogen was abundant. And 24 strains of hydrogen-producing bacteria were isolated from the fermenting material in a biogas digester,which belong to Enter-bacteriaceae and Bacillaceae respectively. There were 5 species in Enter-bacteriaceae while there was only species in Bacillaceae.The propanotyl-alcohol-Clostridium isolated was of stronger hydrogen-producing capability and its starch-utilizing ability is also strong. By combining the media of hydrogen-producing bacteria and methane-producing bacteria for incubation, the production of methane can be raised while CO2content is reduced markedly.

2.7.2　Other Specific Bacteria

Some other specific bacteria were also found in anaerobic digestion.

①De-sulphoribric bacteria-reduce sulphates.

②Lactic acid utilizing bacteriamainly utilizes lactic acid to produce acetic acid and propanic acid,including Streptococcus Sp.,Bacteroides Sp.,and Clostridium Sp.

③Besides, photosynthesizing bacteria were also isolated from biogas digester by some investigators, but their actions involving anaerobic digestion still need further study.