Hydrolysis of by-products from cereal kernels for improved ethanol production

Sammanfattning: This work deals with the hydrolysis of lignocellulosic agricultural residues, by means of combined pretreatment and enzymatic hydrolysis, to be used for ethanol production. Four agricultural by-products, i.e. barley husk, wheat bran and the waste streams of a combined starch and ethanol factory, denoted wheat starch fibres and starch-free fibres B, were investigated. The starch in wheat bran and wheat starch fibres was removed by treatment with amylases, resulting in the materials denoted starch-free bran and starch-free fibres A. Pretreatment of these four materials was performed either by microwave or steam pretreatment with or without the addition of acid. The effect was assessed with enzymatic hydrolysis. A higher sugar yield was obtained with the addition of small amounts of sulphuric acid, although only the pretreatment conditions without the addition of acid were optimised for starch-free fibres A and B. The highest sugar yields obtained after hydrolysis of starch-free bran, starch-free fibres A, starch-free fibres B and barley husk corresponded to 80%, 69% 87% and 68% of the theoretical, respectively. The hydrolysates from starch-free bran and barley husks showed no inhibition in fermentability tests. Simultaneous saccharification and fermentation with S. cerevisiae of a 10% total DM steam-pretreated barley husk resulted in 81% of the theoretical ethanol yield, corresponding to 71% of the ethanol yield based on carbohydrate composition. The use of the wheat fibres and the wheat bran in the combined starch and ethanol factory would increase the ethanol yield in 25 and 20%, respectively. Utilisation of the husk fraction in plants producing ethanol from barley grain could increase the ethanol yield by more than 10%.