Ultrasonic assisted amaranth stem pretreatment for bio-ethanol production

Abstract

An investigation was undertaken to determine the effect of ultrasound on enzymatic hydrolysis rate and enhanced bioethanol yields. Compositional analysis of the feedstock reveals that amaranth lignocellulose contains 36.35% cellulose and 22.57 % hemicellulose. Two sets of experiments were conducted each involving the use of alkaline or acid solutions and ultrasonic irradiations. The effect of energy-input, sonication time, calcium hydroxide and sulfuric acid concentrations (10 and 30 g.kg-1) at a constant biomass loading (50 g.kg-1) was studied. 30 FPU equivalent of cellulolytic enzyme activity was added to each pretreated biomass and incubated at 50°C for 48 hours at pH 4.8. High Performance Liquid Chromatography (HPLC) was used to quantify the total monomeric sugars and ethanol, while the solid residues were characterized by Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). Results show that ultrasonic-assisted dilute acid pretreatment was the most favorable conditions to obtain more fermentable sugars. The highest total sugar yield (350 g.kg-1 substrate) was obtained at 270 kJ/g energy-input for 30 min in presence of 30 g.kg-1 of H2SO4 solution. Pretreatment of amaranth lignocellulose in dilute alkali solution yielded modest total sugar yield (240 g.kg -1 substrate) under similar conditions of 270 kJ.g-1 energy-input for 30 min at 30 g.kg-1of Ca(OH)2 loading. Significant disruption of biomass structure was observable after pretreatment with dilute acid than when dilute alkaline was applied. FTIR spectra show peaks associated with carbon-carbon double bonds, acetyl group and hydroxyl decreasing which is consistent with removal of sugars and oligomers from amaranth lignocellulose. Therefore, a combination of ultrasound irradiations and dilute acid has shown to be effective and promising approach for pretreatment of amaranth stem when fully optimized