SIMULTANEOUS SACCHARIFICATION AND FERMENTATION OF CASSAVA STEMS

SIMULTANEOUS SACCHARIFICATION AND FERMENTATION OF CASSAVA STEMS SACARIFICACIÓN Y FERMENTACIÓN SILMUTÁNEA DE TALLOS DE YUCA HADER CASTAÑO PELÁEZ MSc. Profesor, Politécnico Colombiano Jaime Isaza Cadavid. Medellin, Colombia. JUAN REALES ALFARO MSc. Profesor Universidad Popular del Cesar, Colombia. JOSÉ ZAPATA MONTOYA PhD. Profesor Universidad de Antioquia, Medellín, Colombia. Received for review November 24 th, 2011, accepted March 15th, 2013, final version March, 21 th, 2013 RESUMEN: La investigación evalúa el efecto del tamaño de inóculo y la actividad enzimática sobre la concentración de etanol obtenido a través de la estrategia de proceso Sacarificación y fermentación simultáneas de tallos de yuca pretratados con álcalis. La determinación y validación de las condiciones óptimas de producción de etanol y la evaluación del proceso en biorreactor fueron también objeto de esta investigación. Tallos de yuca con pretratamiento alcalino fueron utilizados como sustrato en una relación sólido: líquido 1:10; el complejo enzimático Accellerase 1500 y la levadura Ethanol Red fueron evaluados a dos niveles a una temperatura de 38 ° C y pH 4.0 a escala de erlenmeyer. Se evaluaron como controles del proceso: Sacarificación fermentación simultáneas sin pretratamiento de los tallos y Sacarificación fermentación independientes de tallos pretratados. Se realizó un análisis de regresión y el modelo obtenido fue maximizado empleando algoritmos genéticos. A las condiciones óptimas identificadas en erlenmeyer fue evaluada la producción de etanol en biorreactor de 5 litros. Se obtuvo una concentración experimental de etanol de 1.88±0.04 %v/v (1.99 %v/v óptimo simulado) con una concentración de inóculo de 1.59 g/L y una concentración de enzima de 13.3 FPU/g, valor aproximadamente 4 veces mayor a la cantidad de etanol producido sin pretratamiento por sacarificación y fermentación independientes de tallos de yuca pretratados. La evaluación del proceso en biorreactor alcanzo una concentración de etanol 20% inferior a la alcanzada a escala de erlenmeyer. PALABRAS CLAVE: Tallos de yuca, Sacarificación, Fermentación, Etanol, Optimización ABSTRACT: This research evaluates the effects of the inoculum size and enzymatic activity on the concentration of ethanol obtained through the simultaneous saccharification and fermentation of alkali-pretreated cassava stems. Other goals for this study include the determination and validation of the optimal conditions for and the evaluation of the process of ethanol production in a bioreactor. Alkaline-pretreated cassava stems were used as the substrate in a solid to liquid ratio of 1:10; the enzymatic complex Accellerase 1500 and the yeast Ethanol Red were evaluated at two levels at a temperature of 38° C and a pH of 4.0 in an Erlenmeyer flask. The following were evaluated as process controls: simultaneous saccharification and fermentation of non-pretreated stems and separate saccharification and fermentation of pretreated stems. A regression analysis was conducted, and the resulting model was maximized using genetic algorithms. At the optimal conditions identified in an Erlenmeyer flask, the production of ethanol in a 5-liter bioreactor was subsequently evaluated. An experimental concentration of ethanol of 1.88±0.04% v/v (1.99% v/v simulated optimum) was obtained using an inoculum concentration of 1.59 g/L and an enzyme concentration of 13.3 FPU/g. This value was approximately four times the quantity of ethanol produced without pretreatment or by the separate saccharification and fermentation of pretreated cassava stems. The evaluation of the process in the bioreactor yielded an ethanol concentration 20% less than that reached in the Erlenmeyer flask. KEYWORDS: Cassava Stems, Saccharification, Fermentation, Ethanol, Optimization 1. INTRODUCTION The threat of depleted oil supplies and environmental concerns have generated interest in biofuels, the production of which has increased dramatically in recent years [1,2]. Ethanol has traditionally been produced using starch and sugary materials [3]; however, given the high cost of these materials and their importance in the production of food and animal fodder, lignocellulosic materials have become interesting and attractive raw materials for the production of ethanol, due to their low cost and abundance [2,4,5]. Dyna, year 80, Nro. 180, pp. 97-104. Medellin, August, 2013. ISSN 0012-7353 98 Castaño et al Lignocellulosic materials are widely available throughout the world at low cost, and this source should be considered for ethanol production with as a way of avoiding competition with the food and agriculture sector. Cassava stems are one source of agricultural residues that could be considered for bioconversion in tropical countries [6,7]. Potential applications of these materials include activated carbon production, energy generation and animal feed; however, the cassava stems are often left in the field, due to their low monetary value, or are burned, causing environmental problems. Cassava stems can be considered to be an alternative source for the production of bioethanol, and the effects associated with leftover cassava could be mitigated [7-9]. Given that the conversion of lignocellulosic biomass into ethanol is difficult because of the complex structure of the plant cell wall, prior treatment is necessary to alter the structural and chemical composition of the lignocellulosic biomass to facilitate rapid and efficient hydrolysis of the carbohydrates into fermentable sugars [10]. Among the pretreatment methods, alkaline pretreatment has generally been used most frequently because it is more efficient for agricultural residues and herbaceous crops [11]. Various studies report that the products of saccharification hinder the complete conversion of cellulose in lignocellulosic materials [12]. Among the cellulose-based ethanol production systems, simultaneous saccharification and fermentation (SSF) has attracted many researchers [12-14]. The SSF process provides several advantages, such as a greater yield in the production of ethanol because the inhibitory compounds released during saccharification are reduced and also because this method eliminates the need for using separate reactors for saccharification and fermentation and reduces inhibitory processes [12]. Using cassava Colombia has an alternative source of biomass for producing bioethanol. In 2009, the production of this tuber was 1,984,427 tons from an area of 182,313 hectares [15]. To date, there are no records in Colombia concerning the use of agricultural residues from cassava crops for the production of ethanol. Implementing comprehensive, cassava-based production of ethanol (using tubers and stems) would enhance the productivity of the ethanol production process, a reality that is reflected in the increase in the energy index of the process. Evaluations of cassava-based ethanol production have produced energy index values between 1.34 and (...truncated)