© 2021 Elsevier LtdFermentation of cattle manure as the sole carbon source and along with the mixtures of switchgrass and wastewater biosolids by hyperthermophilic cellulolytic bacterium, Caldicellulosiruptor bescii was assessed for the first time in the literature. When cattle manure was used as the sole carbon source, a yield of 82.5 NmL/gVSadded was recorded and that is the highest yield reported from dark fermentation studies on cattle manure so far. The mixture of cattle manure with wastewater biosolids and switchgrass was also utilized by C. bescii and statistical analysis of batch tests indicated the highest (antagonistic) interaction when cattle manure and switchgrass were co-fermented. As a co-substrate, wastewater biosolids produced higher amount of hydrogen compared to switchgrass with a yield of 76.5 NmL/g VSadded. The major liquid end product was acetic acid in all fermentation reactors, which can further be used in a two-stage hyperthermophilic dark fermentation-microbial electrolysis cell system for increased hydrogen production.