Energy yield optimization of co-hydrothermal carbonization of sewage sludge and pinewood sawdust coupled with anaerobic digestion of the wastewater byproduct

•Sewage sludge and pinewood sawdust were co-carbonized hydrothermally.•Wastewater byproduct was anaerobically digested to obtain methane.•Hydrothermal temperature was the primary influencing factor for total energy yield.•Maximum energy yield was obtained at 190 °C and 75% sawdust share.•The energy yield of hydrochar and methane reached 86.46% and 3.15%, respectively.