Enhancing Bioethanol Yield from Ravenna Grass (<i>Saccharum ravennae</i>): Optimization of Pretreatment Strategies and Surfactant-Assisted Enzymatic Hydrolysis for Maximum Sugar Yield

Abstract

The high polysaccharide content of Ravenna grass (Saccharum ravennae) made it a viable choice for the generation of biofuel. However, sugar conversion must be optimized for its economic sustainability. The pretreatment of Ravenna grass biomass (RGB) was performed with 2% H2SO4(AC), 2% NaOH (AL), and subsequent H2SO4–NaOH (AC–AL) hydrothermal methods. Enzymatic hydrolysis of all of the pretreated samples, along with raw biomass, was conducted using cellulase from Trichoderma reesei with and without ionic (SDS, CTAB) and nonionic (Tween 20) surfactants (10 mg/mL). The AC–AL-treated RGB was hydrolyzed without the use of surfactants, yielding a maximum sugar yield of 624 mg/g. Regardless of the pretreatment techniques used, adding sodium dodecyl sulfate (SDS) to enzymatic hydrolysis significantly decreased the sugar yield. The inclusion of cetyltrimethylammonium bromide (CTAB) in the hydrolysate also reduced the sugar yield but only marginally. Tween 20 restricts enzyme adsorption to lignin fractions, increasing total sugar production for all of the pretreated samples. The cellulose and xylan digestibility of AL-treated RGB significantly improved by 16.72 and 34.33%, respectively. A maximum sugar yield of 816 mg/g was obtained from the enzymatic hydrolysis of AL-treated RGB using a Tween 20. The addition of Tween 20 produced 0.249 and 0.318 g of ethanol per 1 g of AL- and AC–AL-treated RGB using Saccharomyces cerevisiae as a fermenting organism, respectively. The optimized sugar yield from Ravenna grass enhanced its usability as a second-generation biofuel substrate in commercial uses and can be an alternative to sugar cane bagasse.