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 °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, R_TAD showed 10% higher VS removal efficiency than that of RMAD (RTAD; 43.3%; RMAD: 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 R_TAD and R_MAD 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 (R_TAD; 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.