10-13: Significance of inhibitors produced during dilute acid pre-treatment of wheat straw

Dilute acid hydrolysis is a relatively cost-effective technology for pre-treatment of recalcitrant biomass and production of cellulosic ethanol. However there are potential disadvantages which will limit its applications; such as production of degradation products that are inhibitory to subsequent biomass conversion.  The goals of our research is to determine the nature and concentration of inhibitors produced during dilute acid pre-treatment of wheat straw and their effect on subsequent enzyme hydrolysis. In this study, wheat straw was subjected to dilute sulphuric acid pre-treatment at high temperatures (140-160^oC), varying acid concentrations (0.5, 1.0, 2.0% v/v) and retention times (10, 20, 30, 45, 60 min). The pre-treated substrate was washed with 1.5X water volume and subjected to enzyme hydrolysis for 48h. The pre-hydrolyzate, wash water and enzyme hydrolyzate fractions were individually analyzed for the production of fermentable sugars namely glucose and xylose, and other degradation products using high performance liquid chromatography. It was determined that the optimal conditions for pre-treating the wheat straw were 140^oC, 1.0% v/v sulphuric acid concentration and retention time of 45 min. Degradation products formed during dilute acid pre-treatment were: formic acid, acetic acid, hydroxylmethylfurfural and furfural. Detoxification did not improve inhibitor removal, especially formic acid and acetic acid.  Increase in severity of pre-treatment conditions led to the increase in generation of inhibitors, while reducing sugar yields by 28% from enzymatic hydrolysis. Future research will focus on identifying which inhibitors generated during dilute acid pre-treatment must be avoided, such that the yield of fermentable sugars is increased.