Hydrothermal hydrolysis of starch with CO2 and detoxification of the hydrolysates with activated carbon for bio-hydrogen fermentation

The imminent use of hydrogen as an energy vector establishes the need for sustainable production technologies based on renewable resources. Starch is an abundant renewable resource suitable for bio-hydrogen generation. It was hypothesised that starch hydrolysates from a large (250 mL) hydrothermal reactor could support bioH2 fermentation without inhibition by toxic byproducts.Starch was hydrolysed at high concentrations (40–200 g L−1) in hot compressed water (HCW) with CO2 at 30 bar in a 250 mL reactor, the largest so far for polysaccharide hydrolysis, at 180–235 °C, 15 min. Hydrolysates were detoxified with activated carbon (AC) and tested in biohydrogen fermentations. The maximum yield of glucose was 548 g kg starch−1 carbon at 200 °C. 5-hydroxymethyl furfural, the main fermentation inhibitor, was removed by AC to support 70% more hydrogen production than the untreated hydrolysates. The potential utilization of starch hydrolysates from HCW treatment for upscaled fermentations is promising.

► Starch was hydrolysed in hot compressed water supplemented with CO2. ► CO2 enhanced sugar generation from starch but also increased levels of toxic 5-HMF. ► Activated carbon removed 5-HMF from hydrolysates without affecting sugars. ► Detoxified hydrolysates made more H2 in fermentation with Escherichia coli HD701. ► Study of the larger, scalable reactor moves towards practical hydrolysis in HCW/CO2.