A comparison of two multi stage anaerobic digestion processes: 4 stage-thermophilic and 4 stage-anaerobic digestion with tapered temperature

Two multi-stage anaerobic digestion systems, 4 stage-thermophilic anaerobic digestion (4TAD) and 4 stage-anaerobic digestion with a tapered temperature configuration (4ADT), were studied to evaluate their solid, volatile organic sulfur compounds and indicator organism reduction potentials. The 4TAD showed better solid reduction than the 4DAT, but had a higher volatile organic sulfur content for the dewatered cake. Both 4-stage configurations were superior to single stage mesophilic or thermophilic digesters with the same detention time. However, the lowest organic sulfur content was for the single stage mesophilic digester. Both multi stage anaerobic digestion systems failed to reduce indicator organism DNA even though the standard culturing method (SCM) data satisfied EPA Class A biosolids requirement.