Enhanced ethanol production from mild alkali-treated oil-palm empty fruit bunches via co-fermentation of glucose and xylose

Abstract

Poor or non-utilisation of the xylose fractions of lignocellulosic biomass is a serious impediment to the achievement of energy security through lignocellulosic ethanol. In this work, the potential of sustainable ethanol production from oil palm empty fruit bunches (OPEFB) by co-fermentation of its glucose and xylose components was assessed. Simultaneous co-saccharification and co-fermentation (SScF) was compared with three other fermentation techniques to evaluate bioconversion of mild-alkaline-treated OPEFB for efficient bioethanol production. Hydrolysis was done by the synergistic actions of commercial cellulase (50 FPU/gds) supplemented with on-site crude hemicellulase at unit ratio of 1 FPU: 5 U. After pre-treatment, 79.0% and 79.3% respectively of total glucan and xylan were recovered while 91.9% and 90.6% of the respective polymers were hydrolyzed to fermentable sugars. At 3.4% (w/v) substrate loading, 89.5% theoretical ethanol yield, equivalent of 0.33 g/g raw OPEFB (418.9 L/tonne) was achieved by using SScF. This was higher than 84.9% (0.31 g/g = 397.6 L/tonne raw OPEFB) achieved by separate co-hydrolysis and co-fermentation (SHcF) which is the closest among other fermentation techniques compared. By our knowledge, the yield achieved by the co-fermentation techniques used in this study has not been reported in any previous research which produced ethanol from OPEFB.