Temperature
Temperature plays an important role in bacterial digestion. The optimal function temperature for mesophilic bacteria are 32.2–43.3 °C and 48.9–60 °C for thermophilic bacteria. Thermophilic digestion eliminates more pathogenic bacteria but requires higher energy costs to achieve the higher temperatures required and may be less stable. Digestion slows down or stops completely when the temperature is below 15.6 °C. Maximum conversion occurs at about 35 °C in conventional mesophilic digesters. The amount of methane produced decreases with decreasing temperature [52,102]. Maintaining stable temperatures in the reactor is very important. Fluctuation of temperature inside the digester can cause system failure [52].