Biohydrogen production from barley straw hydrolysate through sequential dark and photofermentation

•Photobiological H2 production on barley straw dark fermenter effluent was realized.•High efficiency biohydrogen production is possible on the lignocellulosic feedstock.•Fe and Mo addition improves photofermentative hydrogen production by Rhodobacter capsulatus.•Omitting yeast extract from dark fermentation does not affect photofermentation.•The highest H2 production of 0.58 mmol/(Lc·h) was achieved with R. capsulatus YO3.

Biohydrogen production by sequential operation of dark and photo-fermentation processes is a promising method to produce hydrogen from renewable resources, in a sustainable way. In this study, barley straw hydrolysate (BSH) dark fermenter effluent (DFE) was used as the biomass feedstock for biohydrogen production through photofermentation. Two different dark fermentation effluents were obtained by performing fermentation with or without addition of yeast extract (YE), using hyperthermophilic dark fermentative bacteria, Caldicellusiruptor saccharolyticus. Photofermentative hydrogen production on BSH DFEs was carried out using purple non-sulfur (PNS) bacterial strains Rhodobacter capsulatus DSM1710 and Rhodobacter capsulatus YO3 (an uptake hydrogenase deleted MT1131 strain). The effects of YE addition during dark fermentation and Fe/Mo supplementation to DFEs on subsequent photofermentation were investigated. Presence of YE in DFEs did not influence the photofermentative hydrogen production. Fe/Mo supplementation of the effluents improved the H2 production on both DFEs, regardless of the strain used. The highest productivity of 0.58 mmol/(Lc·h) was achieved by R. capsulatus YO3 on Fe/Mo supplemented BSH DFE that had no YE. Biohydrogen production on BSH DFE was achieved at a high rate and yield, showing that it can be used as a feedstock for photofermentative hydrogen production.