Which temperature range is most commonly used for anaerobic digesters?

• A. Psychrophilic
• B. Thermophilic
• C. Hyperthermophilic
• D. Mesophilic

Answer: (D)

Digesters are run at different temperature ranges to favor different microbial communities, which affects how fast digestion occurs, how stable the process is, and how much energy is needed for heating. The most common approach for anaerobic digestion is mesophilic operation, which sits roughly in the 30–40°C range, with an optimum around 35°C. This temperature provides a reliable balance: solid methane production, good process stability in the face of feed variability, and moderate heating energy requirements. Thermophilic digestion, around 50–60°C, can speed up digestion and improve pathogen destruction but demands much more heating and tighter control, making it less forgiving. Psychrophilic and hyperthermophilic ranges are extreme and impractical for standard municipal digesters. So, mesophilic operation is by far the most widely used.