Biohythane production via single-stage anaerobic fermentation using entrapped hydrogenic and methanogenic bacteria

[Display omitted] •Continuous and simultaneous production of H2 and CH4 in a single digester.•Mixture of separately-entrapped hydrogenic/methanogenic bacteria was used.•Tested biomass volume ratios of entrapped H2 and CH4 beads were 4/1–1/4.•Biohythane production rates were 381–480 mL/L-d with H2 content of 1–75%.•Biomass volume ratio 2/3 (weight ratio 1/1.5) had peak biohythane production. This study demonstrates the continuous biohythane production in a single-stage anaerobic digester using a biomass mixture of separately entrapped hydrogenic and methanogenic bacteria (H2- and CH4-producing bacteria, respectively). The entrapped hydrogenic/methanogenic bacteria biomass ratios of 1/4, 2/3, 3/2 and 4/1 were tested and shown to have a great effect on the single-stage biohythane production performance. At steady-states, the cultivations had biohythane production rates in the range of 381–480 mL/L-d, with H2 content in biohythane (HCH) varying from 1% to 75% (v/v) and chemical oxygen demand removal efficiencies (TCODre) of 57.6–81.9%. Biomass ratio 2/3 (weight ratio 1/1.5) resulted in peak biohythane production with H2 and CH4 production rates being 64.6 and 395 mL/L-d, respectively, HCH 15% and TCODre 74.4%. The novelty of this work is to show the potential of producing biohythane from an innovative single-stage dark fermentation system using entrapped hydrogenic and methanogenic bacteria.