A two-stage thermophilic hydrogen fermentation and mesophilic methane production from paper sludge was successfully explored. The maximum hydrogen and methane potential were 0.165 Lig VS and 0.376 Lig CODeffluent, respectively with Clostridium thermocellum augmentation. 63 L of hydrogen and 122 L of methane were recovered from 1 kg Paper sludge (PS, dry weight) with an energy yield of 4.5 MJ/kg PS, 50% higher compared to the single-stage anaerobic digestion (94 L CH4, 3.0 MJ/kg PS). The bacterial community of second-stage process was dominated by genus Propionispira, Mesotoga and Amino-becterium with stability, whereas the bacterial structure in single-stage process presented dynamic changes where genus Acetivibrio and Fibrobacter played an indispensable role. However, Genus Methanosaeta, Methanosarcina, Methanobacterium and Methanospirillum existed stably and predominantly in the archaeal community of single-stage and second-stage processes. The present study suggests the potential application of the established two-stage process in valorization of low-value waste biomass. (C) 2019 Elsevier Ltd. All rights reserved.