3.1　Strict Anaerobic Environment

All microbes that play an important role in biogas digestion are strict anaerobic bacteria. They include the acid-forming bacteria and methane-forming bacteria.

The methane-forming bacteria are very sensitive to oxygen and will die in the air within only a few minutes. The digestion would be handicapped by even the slightest trace of oxygen. Thus, the strict anaerobic environment is a prerequisite for biogas digestion.

The sealed digester has created an anaerobic environment for biogas microbes. The term “ORP” (oxidation-reduction potential) has been used generally to indicate the extent of anaerobic state.

As biogas digestion process is completed by a series of oxidative reduction reactions, it has a close relation with the “ORP” in the environment.

With the charging of raw materials, a lot of oxygen entered the digester and the ORP was high. But during the initial period in the sealed digester, the dissolved oxygen was quickly exhausted by aerobic and facultative anaerobic bacteria, which made the ORP gradually lower. Hence, if the digester is in a strict sealed condition, it is unnecessary to adjust the ORP.