Thermophilic Anaerobic Digestion of Waste Activated Sludge versus Mesophilic Anaerobic Digestion

Dissimilarities between thermophilic and mesophilic anaerobic digestion of waste activated sludge (WAS) Typical WAS with total solids (TS) concentrations of 30 and 60 g/L were digested anaerobically in a batch digester at mesophilic and thermophilic temperatures. Solids reduction, total COD changes, the production of different volatile fatty acids (VFAs), the quality and quantity of the produced biogas were investigated and compared for both temperatures. The mesophilic digestion took place after 32 to 36 days with slightly more methane production and removal of organics than thermophilic digestion. The results showed that there was no significant difference between thermophilic and mesophilic digestion with respect to the gas composition. Among the VFAs, as the key intermediates, only propionate accumulated during sludge anaerobic digestion at mesophilic and thermophilic temperatures. Keywords—Thermophilic anaerobic digestion, Mesophilic anaerobic digestion, Waste activated sludge, Volatile fatty acids