ULTRASONIC ASSISTED AMARANTH STEM PRETREATMENT FOR BIO-ETHANOL PRODUCTION Idan Chiyanzu, Amanda Mditshwa, Sanette Marx Focus Area: Energy Systems, School of Chemical and Minerals Engineering, North-West University (Potchefstroom Campus), Potchefstroom, South Africa, Tel: +27 18 299 1988, Fax: +27 18 299 1535, Email:24043605@nwu.ac.za 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 -1 of 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. Keywords: Ultrasound, pretreatment, dilute alkaline, dilute acid, amaranth, bioethanol. 1 INTRODUCTION The global demand for energy is increasing rapidly because of high fuel consumption and growing industrialization. The increased energy demand has highlighted the limited supply of fossil based energy and the urgent need for renewable alternatives (Sunday, 2011). According to Sunday [1] approximately 2.4 billion people worldwide lack access to modern fuel. Fossil- based fuels are widely used for energy resources and are major contributors to environmental pollution [2]. Increasing environmental pollution has resulted in global climate change. Researchers have been driven to find alternative ways that produce a fuel that is ecological friendly, sustainable, and affordable. Biofuels are fuels derived from biomass such as renewable organic materials from plants or animals [3]. Biomass feedstock is classified into: first, second and third generation feedstock. The first generation feedstock are those crops that are used mostly as food and feed for humans and are rich in sugar, oil, and starch [4]. However the use of first generation feedstock biofuel production has raised arguments that fuels competes with food and is responsible for increase in food prices [5]. The latter has resulted in the shift towards using second generation feedstock. Second generation feedstock are dominated by lignocellulosic biomass such agricultural residues [6] and also municipal and industrial waste [5]. Lignocellulose consists of cellulose and hemicellulose, which are converted into sugars through chemical pretreatment and biological processes and eventually fermented to bioethanol [2]. However, second generation biofuels has raised concern over the land use requirements and changes and as a result researchers have directed the focus towards third generation fuels [6]. Third generation biofuels produced from microscopic organisms are considered to be viable alternative energy resource that do not possess the major drawbacks associated with first and second generation biofuels [7]. Third generation feedstock are non-food crops such as microalgae [2] and microbes [7]. Biofuel feedstock can be converted into solid, liquid, and gaseous form of biofuels. Amongst all the liquid biofuels, biodiesel and bioethanol, are the most studied and promising as alternative fuels or used as blends with petroleum petrol [8]. Ethanol (ethyl alcohol), one of the liquid fuels made from biomass, has for many years been applied as oxygenate to petroleum fuels providing significant reduction in particulate and NOx emissions from their combustion [9]. Many more preference for use of bioethanol include its high-octane number, high compression ratio and a shorter burn time, and thus it has a theoretical efficiency advantage over petrol in an internal-combustion engine. Currently, the most viable route for ethanol production is by means of first- generation feedstock such as sugar and starch. Amaranth is a potential second generation feedstock for ethanol production that is relatively cheap. Amaranth possesses characteristics such as fast growth rate, good tolerance to stress and high potential biomass yield [10]. It has a C4 photosynthetic pathway and nitrogen acquisition which makes it a fast growing plant. Amaranth is also known to absorb heavy metals from surrounding soil and can thus be used for the rehabilitation of contaminated soils [11]. Various types of pretreatment methods for production of bioethanol such as physical, physico-chemical, chemical and biological methods and combinations thereof [12] has been investigated. Application of ultrasound irradiation in combination with dilute acid or alkaline pretreatment strategies has been shown to me more effective in breaking down lignocellulose material into fermentable sugars than just the alkaline or acid pretreatment [13]. Application of ultrasound-assisted pretreatment under selected conditions can increase the overall bioethanol yield rapidly through the increased porosity of cellulose fibre [13] and the cleavage of glycosidic linkages in lignin [14]. It can also promote decrease of mass transfer limitations and improve hydrolysis [15]. 23rd European Biomass Conference and Exhibition, 1-4 June 2015, Vienna, Austria 356