Enhancing bioethanol productivity using alkali-pretreated empty palm fruit bunch fiber hydrolysate

Abstract

Empty palm fruit bunch fiber (EPFBF) is a renewable resource in oil palm plantations that can be used for lignocellulosic bioethanol production. To enhance ethanol productivity with high-lignin-content EPFBF, the biomass was prepared with an alkali-thermal pretreatment (sodium hydroxide, 121°C, 60 min). The delignification yield was 55.4-56.9%, in proportion to the amount of sodium hydroxide, from 0.5 to 2.0 M. The lignin and hemicellulose contents of EPFBF were reduced by the pretreatment process, whereas the proportion of cellulose was increased. During enzymatic saccharification using Celluclast 1.5L and Novozyme 188 enzyme cocktails, about 62% of glucan was converted to a fermentable sugar. In simultaneous saccharification and fermentation, comparison among three ethanologenic yeast strains showed Saccharomyces cerevisiae W303-1A to be a candidate for maximum ethanol yield. In a batch fermentation with alkali-pretreated EPFBF hydrolysate, 21 g/L ethanol was obtained within 28h, for a production yield of 0.102g ethanol/g dry EPFBF or 0.458g ethanol/g glucose. Moreover, a fed-batch fermentation produced 33.8±0.5g/L ethanol with 1.57g/L/h productivity in 20h. These results show that the combination of alkaline pretreatment and biomass hydrolysate is useful for enhancing bioethanol productivity using delignified EPFBF.