Dry anaerobic digestion of food waste at mesophilic and thermophilic temperature
Dry plug flow anaerobic digestion (AD) is a relatively new technology for the biological treatment of food waste. To avoid costly external hygienisation, most Swedish dry AD plants wish to operate under thermophilic conditions. However, source separated organics (SSO) with high nitrogen content increase the risk for ammonia inhibition at higher temperatures. This project studied how the operating temperature affects microbial community composition, sanitation, process stability and energy efficiency at existing dry AD plants using food waste as main substrate.
Process data, substrate and digestate samples from four dry AD plants were collected and analyzed. All plants used SSO as their main substrate but were operated at different temperatures (38–39, 42 and 54 °C). The microbial community analysis demonstrated that each process in the present study had different microbial profiles and that operating temperature strongly influenced the community structure. All processes operated at an ammonia level that is known to inhibit methanogens that directly use acetate for methane formation. The microbial community supported this and showed that a hydrogen-utilizing methanogen (Methanoculleus bourgensis) had an important role for efficient methane production in all processes.
The hygenisation analysis indicated that a temperature >42 and