Potential of barley straw for high titer bioethanol production applying pre-hydrolysis and simultaneous saccharification and fermentation at high solid loading

Abstract

Barley straw (BS) is considered a good candidate for fuel-ethanol production due to its abundance and high carbohydrate content. Economic viability of the process requires ethanol titer in fermentation broth >4% (w/v) which is considered to be the benchmark for an efficient distillation. Mild alkaline pretreatment of BS resulted in 74% and 45% lignin and hemicellulose removal, respectively. Alkali treated barley straw (ATBS) was hydrolyzed at 15% (w/v) substrate concentration, using commercial cellulases (Cellic® CTec2). Highest glucose release was 91.19 g/L (hydrolysis yield 82%). Models based on first and second order cellulase deactivation kinetics satisfactory predicted the behavior of glucose release during enzymatic hydrolysis of ATBS, however the first order model appears to fit better. ATBS, at high solids loading (15% and 20% w/v), was converted to bioethanol applying pre-hydrolysis and simultaneous saccharification and fermentation (PSSF). Highest ethanol production was achieved after 16 h pre-hydrolysis. As substrate loading increased from 15% to 20%, ethanol concentration increased from 39.55 to 46.62 g/L. Mass balance of PSSF showed that the reduction of ethanol yield when solid loading increases could be attributed to the decrease in cellulose enzymatic conversion.