Laccase-mediator assisted enzymatic hydrolysis of aqueous ammonia soaking pretreated sugarcane bagasse at high solids concentration and fermentation to bio-ethanol by Candida tropicalis

The most important step in bioethanol production process is enzymatic hydrolysis of lignocellulosic biomass to fermentable sugars. Production of >5% ethanol during fermentation is desirable for economically sustainable... [ view full abstract ]

The most important step in bioethanol production process is enzymatic hydrolysis of lignocellulosic biomass to fermentable sugars. Production of >5% ethanol during fermentation is desirable for economically sustainable bioethanol production process, which requires a minimum of ≥10% fermentable sugars in the hydrolysate. Formation of 10% fermentable sugars, mostly glucose and xylose from lignocellulosic biomass has been reported for enzymatic hydrolysis at ≥20% solids loading of lignocellulose. Enzymatic hydrolysis at high solid loadings involves certain challenges such as high stirring resistance in bioreactor and limitation of mass and heat transfer which results in reduced hydrolysis yields. In the present work fed-batch process has been optimized for biomass feeding time and enzyme loading to achieve >20% solid loading of low temperature aqueous ammonia pretreated sugarcane bagasse. Laccase – mediator assisted enzymatic hydrolysis was performed to enhance the sugar yields. The present method improved yields of sugars when compared with cellulase hydrolysis. The ethanol titer obtained from the biomass hydrolysate was more than 60 g/L. The ethanol concentration achieved in our study was higher than the level reported for 2^nd generation bioethanol produced from ammonia soaking pretreated biomass. The results also proved that low energy pretreatments also have the potential to produce high titer of bioethanol