Design of Anaerobic Digestion Systems

Two improvements made in digestion systems in the last generation are temperature control and digester mixing. Other environmental factors can also be more closely controlled to obtain better digester performance. Thorough digester mixing will permit total use of the digester volume for microbial activity. Return of sludge from a separation device to the mixed digester permits short liquid detention times in the digestion system without sacrificing the long solids retention time necessary for adequate stabilization of the organic load to the system. Sludge recycle increases the concentration of active organisms in the digester. Volatile acid concentration will vary because of environmental and operation changes. Increased loading rates increase the buffer capacity of the system at the same time making better use of digester volume. Illustrations of how these factor shave been used in the design of anaerobic systems are provided.