Effect of four pretreatments on enzymatic hydrolysis and ethanol fermentation of wheat straw. Influence of inhibitors and washing

•Four pretreatments were compared for bioethanol production from wheat straw.•Pretreatment efficiency is linked to structural changes in straw and lignin removal.•Water washing removes inhibitory compounds generated during pretreatment.•Basic pretreatment increases sugar release but also inhibitor production.•Alkaline peroxide is an efficient wheat straw pretreatment for producing bioethanol.

Pretreatment is essential in the production of alcohol from lignocellulosic material. In order to increase enzymatic sugar release and bioethanol production, thermal, dilute acid, dilute basic and alkaline peroxide pretreatments were applied to wheat straw. Compositional changes in pretreated solid fractions and sugars and possible inhibitory compounds released in liquid fractions were analysed. SEM analysis showed structural changes after pretreatments. Enzymatic hydrolysis and fermentation by Pichia stipitis of unwashed and washed samples from each pretreatment were performed so as to compare sugar and ethanol yields. The effect of the main inhibitors found in hydrolysates (formic acid, acetic acid, 5-hydroxymethylfurfural and furfural) was first studied through ethanol fermentations of model media and then compared to real hydrolysates. Hydrolysates of washed alkaline peroxide pretreated biomass provided the highest sugar concentrations, 31.82 g/L glucose, and 13.75 g/L xylose, their fermentation yielding promising results, with ethanol concentrations reaching 17.37 g/L.