Common recurring problems associated with anaerobic digesters are loss of heating capability and maintenance of optimum digester temperature. An acceptable and uniform temperature should be maintained throughout the digester to prevent localized pockets of depressed temperature and undesired bacterial activity. Variations in temperature of even a few degrees affect almost all biological activity including the inhibition of some anaerobic bacteria, especially methane-forming bacteria. Adequate mixing of the digester content prevents the development of localized pockets of temperature variation. Most methane-forming bacteria are active in two temperature ranges. These ranges are the mesophilic range from 30 to 35°C and the thermophilic range from 50 to 60°C. At temperatures between 40°C and 50°C, methane-forming bacteria are inhibited. Digester performance falters somewhere near 42°C, as this represents the transition from mesophilic to thermophilic organisms. Although methane production can occur over a wide range of temperatures, anaerobic digestion of sludge and methane production at municipal wastewater treatment plants is performed in the mesophilic range, with an optimum
temperature of approximately 35°C Whenever digester temperature falls below 32°C, close attention should be paid to the volatile acid-to-alkalinity ratio. Volatile acid formation continues at depressed temperatures, but methane production proceeds slowly. Volatile acid production can continue at a rapid rate as low as 21°C, whereas methane production is essentially nonexistent. Therefore, 32°C is the minimum temperature that should be main-tained, and 35°C is the preferred temperature.
temperature of approximately 35°C Whenever digester temperature falls below 32°C, close attention should be paid to the volatile acid-to-alkalinity ratio. Volatile acid formation continues at depressed temperatures, but methane production proceeds slowly. Volatile acid production can continue at a rapid rate as low as 21°C, whereas methane production is essentially nonexistent. Therefore, 32°C is the minimum temperature that should be main-tained, and 35°C is the preferred temperature.
