Kinetic study of ethanol production from different sizes of two-step pretreated oil palm trunk by fed-batch simultaneous saccharification and fermentation

Abstract

Importance of the work: The particle size of lignocellulosic material exerts a significant impact on pretreatment and enzyme hydrolysis. Objectives: To study the particle size impact of pretreated fibers on enzyme hydrolysis and ethanol production using simultaneous saccharification and fermentation (SSF). Materials & Methods: In this study, oil palm trunk (OPT) chips were pretreated using a two-step pretreatment. The pretreated fibers of varied sizes (40 mesh, 40-60 mesh, 60 mesh and non-milled fibers) were used as substrates with different enzyme and substrate feeding approaches for efficient ethanol production based on SSF. Results: The 40 mesh particles produced elevated levels of: ethanol concentration (CP), 43.07 g/L; ethanol productivity (QP), 0.47 g/L/hr; ethanol yield (YP/S), 0.47 g/g; and ethanol theoretical yield, 90.26%. A further reduction in pretreated particle size from 40 mesh to 40-60 and 60 mesh significantly reduced the ethanol production and ethanol productivity rate. The highest QP rate in the log phase was observed with 40 mesh (0.994 g/L/hr), followed by non-milled fibers (0.809 g/L/hr). The optimized particle fibers (40 mesh) were further used for fed-batch SSF, which was carried out using four different sets of experiments. Each set was based on a strategy of feeding enzymes (celluase and β-glucosidase) and sterilized fibers. Main finding: Out of studied sets of experiments, the strategy with enzymes fed at the start-up of fed-batch SSF and the addition of fibers at 12 hr, 24 hr and 36 hr produced a significantly higher ethanol concentration (41.65 g/L).