Comparison of two advanced anaerobic digestions of sewage sludge with high-temperature thermal pretreatment and low-temperature thermal-alkaline pretreatment

Semi-continuous experiments were conducted to compare the performances and energy efficiencies of two advanced anaerobic digestions (AAD) of sewage sludge with high-temperature thermal pretreatment (HTTP, 160 +/- 1 degrees C and 0.55 MPa for 30 min) and low-temperature thermal-alkaline pretreatment (LTTAP, 60 +/- 1 degrees C and pH 12.0 +/- 0.1 for 30 min), which had similar sludge disintegration degree (9.44-9.48%). At the steady period of a SRT 20 d, the two AAD had similar methane production (150.22 +/- 9.55 ml/L/d and 151.02 +/- 12.56 ml/L/d) and organic matter removals (22.54 +/- 2.84% and 23.15 +/- 2.46% for volatile solids- VS). The results of high-throughput sequencing showed that the methanogenic pathways of the two AAD were strictly hydrogenotrophic (AAD with HTTP) and hydrogenotrophic/acetoclastic methanogenesis (AAD with LTTAP), respectively. The energy balance analysis suggested that the AAD with LTTAP was superior to that with HTTP because the former had a higher energy efficiency (1.610) than the latter (1.358).