Chapter 2　Biochemistry and Microbiology of Biogas Fermentation

Biogas generation is the process of catabolic metabolism of organic matter which is degraded by microorganism under the condition of air absence, certain moisture, certain temperature and pH value. The metabolic microorganism is called biogas fermentative microorganism, or anaerobic digestive microorganism. The process is called biogas fermentation, or anaerobic digestion, or methane fermentation.

Some characteristics of the biogas fermentation are as follows:

①The energy consumption of biogas anaerobic microorganism is 1/20 or 1/30 of aerobic microorganism. In the anaerobic digestion, we can obtain 100～300 calorie free energy, while we can obtain 3000 calorie free energy in the aerobic digestion with the degradation per gram COD.

②The biogas fermentation can treat organic waste water which has a COD value above 10000mg/L, while the aerobic digestion can only treat organic waste water with a COD value below 1000m/L.

③The biogas fermentative microorganism can degrade variety waste due to its low demand for nutrient.

④The biogas fermentation is more strongly influenced by temperature.

⑤The biogas fermentation residues can be separated from broth easily. Compared with ordinary compost, the biogas anaerobic fermentation not only uses methane, but also keeps nitrogen. The two metabolism processes are as follows (Fig.2.1):

Fig.2.1　The decompose process of organic waste