Knowledge Base

The key difference between mesophilic and thermophilic digestion is the operating temperature of the digester. Mesophilic digestion takes place at around 40°C, while thermophilic digestion operates at approximately 55°C. Both approaches use naturally occurring micro-organisms to break down organic material and produce biogas, but they differ in speed, stability, and the types of feedstocks they manage most effectively.

HoSt biogas plants can operate in both conditions. In practice, thermophilic operation is usually applied only to after-digesters: running the primary digester, where most of the organic load is present, and around 70-80% of the organic matter is converted to biogas at thermophilic temperature is considered too risky, since the process runs faster and is less stable. This risk is greater still with high-nitrogen feedstocks, such as significant quantities of chicken manure, which can acidify the digestate and kill the bacteria inside the tank. For this reason, thermophilic conditions are generally reserved for after-digesters, while primary digesters are kept mesophilic. The right configuration is assessed case by case, based on feedstock type, project location, and the intended use of the digestate.