Digestion performance of various combinations of thermophilic and mesophilic sludge digestion systems

Various combinations of single- and multi-stage anaerobic and aerobic-anaerobic digestion systems were studied to evaluate their solids reduction potential with capabilities to control sulfur-based biosolids odor compounds. All the multi-stage digestion systems removed more volatile solids than the single-stage anaerobic digestion systems, even at the same overall retention time. However, digestion systems with mesophilic digestion as the final stage showed a much lower headspace organic sulfur content in the dewatered biosolids than the systems with thermophilic digestion as the final stage. This observation leads to the conclusion that placing a mesophilic anaerobic digestion system at the end of multi-stage digestion systems will enable greater sulfur-based odor reduction from dewatered biosolids with greater solid reduction than single-stage mesophilic or thermophilic digestion systems.