Direct fermentation of fodder maize, chicory fructans and perennial ryegrass to hydrogen using mixed microflora

This study examined the feasibility of producing hydrogen by direct fermentation of fodder maize, chicory fructooligosaccharides and perennial ryegrass (Lolium perenne) in batch culture (pH 5.2–5.3, 35 °C, heat-treated anaerobically digested sludge inoculum). Gas was produced from each substrate and contained up to 50–80% hydrogen during the peak periods of gas production with the remainder carbon dioxide. Hydrogen yields obtained were 62.4 ± 6.1 mL/g dry matter added for fodder maize, 218 ± 28 mL/g chicory fructooligosaccharides added, 75.6 ± 8.8 mL H2/g dry matter added for wilted perennial ryegrass and 21.8 ± 8 mL H2/g dry matter added for fresh perennial ryegrass. Butyrate, acetate and ethanol were the main soluble fermentation products. Hydrogen yields of 392–501 m3/hectare of perennial ryegrass per year and 1060–1309 m3/hectare of fodder maize per year can be obtained based on the UK annual yield per hectare of these crops. These results significantly extend the range of substrates that can be used for hydrogen production without pre-treatment.