Manganese doped magnetic carbon (MDMC) was synthesized to enhance bio-hydrogen (H-2) process under the mesophilic and thermophilic conditions. MDMC characterization showed that MnFe2O4, Fe2O3 and few MnCO3 were adhered to activated carbon and formed MDMC whose specific surface area and average pore size were 110.92 m(2) . g(-1) and 3.2 nm, respectively. Suitable concentration of MDMC promoted while high dosage suppressed the H-2 production of glucose through anaerobic fermentation by heat-treated sludge. The highest yields of 211 and 148 ml H-2/g glucose were obtained at 400 mg/L (37 degrees C) and 600 mg/L MDMC (55 degrees C), being 55.8% and 19.3% higher than that of the control groups, respectively. Some possible mechanisms were proposed as follows: appropriate concentration of MDMC provided considerable and favorable sites for microbial colonization, released trace elements (e.g. Mn, Fe) into liquid for the microbial growth, and promoted the direct interspecies electron transfer. Moreover, MDMC could be recycled by magnetic separation after bio-H-2 process due to its magnetism. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.