Fermentative production of hydrogen from a wheat flour industry co-product

The global flour industry produces 96 million ton/year of wheatfeed, which is mainly used for animal feed. This co-product is high in carbohydrates and potentially a significant substrate for biohydrogen production. A 10 l bioreactor, inoculated with sewage sludge, was operated on wheatfeed (10 g l −1) at pH 5.5 and 35 °C in batch and semi-continuous mode (15 h hydraulic retention time (HRT)). Wheatfeed hydrolysate was also investigated in continuous mode (15 h HRT). NaOH–H 2O 2 treatment of 25 g l −1 wheatfeed resulted in hydrolysate containing on average 8.1 g l −1 total sugar. Hydrogen yields of 64 and 56 m 3 H 2 per ton dry weight were produced from wheatfeed in batch and 56 m 3 H 2 per ton dry weight of wheatfeed in semi-continuous mode. Hydrogen yields from hydrolysate were only 22 and 31 m 3 H 2 per ton dry weight, (or 0.9 mol H 2 per mol hexose degraded, assuming all sugar is hexose). Fermentation of unhydrolysed wheatfeed is therefore recommended. It is calculated that approximately 264 m 3/ton of CH 4 can be produced from a subsequent anaerobic digestion stage. The biohydrogen produced (diesel equivalents) from the 1.2 million ton/year of wheatfeed in the UK would be more than twice that required for transportation by the UK flour industry.