Comparison of Single-stage Thermophilic and Mesophilic Anaerobic Sewage Sludge Digestion

In this study, single-stage continuous anaerobic reactors to treat sewage sludge were operated under different temperature (55 and 35 degrees C; R-TAD and R-MAD) to evaluate the reactor stability and performance of the thermophilic and mesophilic anaerobic digestion. During the overall digestion, both anaerobic reactors maintained quite stable and constant pH and total alkalinity (TA) values in the range of 6.5-8.0 and 3-4 g CaCO3/L, respectively. After the start-up period, RTAD showed 10% higher VS removal efficiency than that of R-MAD (R-TAD; 43.3%; R-MAD : 33.6%). Although organic acids such as acetic and propionic acid were detected in both anaerobic reactors at the start-up period, all organic acids in RTAD and RMAD were consumed at the steady state condition. Also RTAD showed 31.4 % higher methane production rate (MPR) than that of RMAD at the steady state condition (RTAD; 243 mL CH4/L/d; R-MAD : 185 mL CH4/L/d). Meanwhile, the experimental results indicated similar methane yield between R-TAD and R-MAD.