Combination of hydrogen fermentation and methanogenesis to enhance energy conversion efficiency from trehalose

•Trehalose was microwaved with dilute acid to improve glucose yield.•Hydrolyzed trehalose was fermented by hydrogenogens to improve dark H2 yield.•H2 yield from trehalose was markedly enhanced by dark- and photo-fermentation.•Cogeneration of H2 and CH4 increased energy conversion efficiency.

Trehalose was pretreated by microwave heating with dilute acid to improve glucose yield and hydrogen production during dark-fermentation. An optimal glucose yield of 0.95 ± 0.08 g/g-trehalose was obtained when trehalose was pretreated by microwave heating with 1% dilute H2SO4 for 25 min at 120 °C. The hydrolyzed trehalose was inoculated with HPB (hydrogen-producing bacteria) to produce hydrogen during dark-fermentation. The residual solution of dark-fermentation was reused by PSB (photosynthetic bacteria) during photo-fermentation. The residual solution of photo-fermentation was reused by MPB (methane-producing bacteria) during methanogenesis. The maximum yields of hydrogen and methane were 731.3 ± 33.6 ml/g-trehalose and 116.9 ± 4.3 ml/g-trehalose. The sequential generation of hydrogen and methane from trehalose remarkably enhanced the energy conversion efficiency from 47.2 ± 2.2% in hydrogen fermentation to 72.2 ± 3.1% in combined hydrogen fermentation and methanogenesis.