Study of acid hydrolysis and submerged fermentation parameters in second generation ethanol production using cassava waste

Abstract

Biofuels are an alternative to reduce the environmental impacts caused by the use of petroleum-based fuels. Second generation ethanol comes from lignocellulosic materials that are little used or discarded in the environment, including agro-industrial waste. These residues are rich in sugars that can be converted by ethanol-producing microorganisms. In this context, the present work uses cassava waste (Manihot esculenta Crantz) obtained during the processing of starch as a raw material for the production of cellulosic ethanol, as well as evaluating different parameters in acid hydrolysis and during submerged fermentation using the strain Saccharomyces cerevisiae ATCC 26602. Experiments of acid hydrolysis of these residues with sulfuric acid in concentrations of 0.5% to 5.0% (v/v) were carried out. The results demonstrated that 2.0% H₂SO₄ for 10 min. reaction at 121 ºC/1.1 atm in an autoclave reached the highest release of reducing sugars present in the residue (131.09 g.L^-1). The ideal conditions for alcoholic fermentation using yeast were pH 6.5, temperature of 35 ºC, without rotation and initial reducing sugar concentration of 50 g.L^-1, resulting in 21.23 g.L^-1 of ethanol with productivity of 1.86 g.L^-¹.h^-¹ and theoretical yield of 96.5% after 12 hours of fermentation. The results indicated that the cassava waste serve as a potential substrate for the production of second generation ethanol. Thus, this study provides data on the most suitable conditions for the use of these industrial wastes aiming at the generation of a renewable fuel, an increasingly attractive feature for the world, where the economic and environmental concern is growing.