Bioreactor performance and methanogenic population dynamics in a low-temperature (5-18 °C) anaerobic fixed-bed reactor

► Bioreactor performance and methanogenic population dynamics in a fixed-bed reactor under low-temperature conditions are firstly reported. ► The reactor has a good anaerobic sludge granules condition and showed stable and considerable methane content in biogas. ► 17 °C and 15 °C were temperature thresholds when the fixed-bed reactor was operated under low temperature conditions. ► Methanomicrobiales played an important role and might be the dominant methanogens in fixed-bed reactors. ► Large numbers of Methanomicrobiales and Methanosaetaceae stably adhered and proliferated to carbon fiber carrier.