Developing a unique microbial hydrolysis process for converting lignocellulosic waste into reducing sugars

Abstract

This thesis attempted to develop a unique microbial hydrolysis process for converting lignocellulosic waste into reducing sugars for subsequent bioethanol or biochemical production. Five specific inoculated sources including 1-year compost (C1), 4-month compost (C4), aerated activated sludge (AAS), garden soil (GS) and guts of mealworm in tropical area were used to investigate the bioconversion of lignocellulosic waste to reducing sugars. Sixteen bacterial and 3 fungal strains were successfully isolated corresponding to most of the major bands detected by denaturing gradient gel electrophoresis analysis. The best microbial cocktail for high reducing sugars production, including the isolates of Microbacterium sp. F28, Tsukamurella sp. C35, Pseudallescheria sp. D42 and Bacillus sp. F4, was defined. The maximum reducing sugars yield by this combination was 165.2 mg/g-lignocellulosic waste within 24-h. A central composite design (CCD) and response surface methodology (RSM) were employed in designing the experiments to determine the optimum conditions for reducing sugars production, three types of pretreatment methods including organosolv pretreatment, liquid hot water pretreatment and diluted sulfuric acid pretreatment were explored to enhance reducing sugars yield. A maximum reducing sugars yield of 173.1 mg/g lignocellulosic waste was obtained under pH5.8, temperature 56.9ºC and 28.9 g/L of initial lignocellulosic waste concentration after organosolv pretreatment experiment. The maximum reducing sugars yield after optimization in this study was higher than some of enzymatic hydrolysis and meanwhile faster and cost effective. Microbial hydrolysis process could therefore be an alternative method for lignocellulose hydrolysis.