Biohythane production via single-stage fermentation using gel-entrapped anaerobic microorganisms: Effect of hydraulic retention time

[Display omitted] •A single-stage biohythane production used entrapped hydrogenic/methanogenic microbes.•HRT markedly affected the biosystem performances.•Biohythane production rates were 0.44–15.8 L/L-d with H2 contents of 7.3–84.6%.•HRT 12 h resulted in peak biohythane production outcomes.•Caproiciproducens/Methanobacterium dominated H2/CH4 production. Research of single-stage anaerobic biohythane production is still in an infant stage. A single-stage dark fermentation system using separately-entrapped H2– and CH4-producing microbes was operated to produce biohythane at hydraulic retention times (HRTs) of 48, 36, 24, 12 and 6 h. Peak biohythane production was obtained at HRT 12 h with H2 and CH4 production rates of 3.16 and 4.25 L/L-d, respectively. At steady-state conditions, H2 content in biohythane and COD removal efficiency were in ranges of 7.3–84.6 % and 70.4–77.9%, respectively. During the fermentation, the microbial community structure of the entrapped H2-producing microbes was HRT-independent whereas entrapped CH4-producing microbes changed at HRTs 12 and 6 h. Caproiciproducens and Methanobacterium were the dominant genera for producing H2 and CH4, respectively. The novelty of this work is to develop a single-stage biohythane production system using entrapped anaerobic microbes which requires fewer controls than two-stage systems.