Investigating the Effects of Water Interactions in Lignocellulosic Materials on High Solids Enzymatic Saccharification Efficiency

Recent fluctuations in gas prices and growing concern over climate change brought on by the use of fossil fuels have lead to increasing development of alternative and renewable energy sources. One promising solution is the development of biofuels derived from lignocellulosic biomass, an abundant and relatively low cost material. Processing under high solids conditions will produce a higher final ethanol concentration, will require less energy to process and purify, and will generate less wastewater overall. Additional benefits includes a reduction in the size of the equipment needed, which lowers capital costs, a reduction in production costs, and increased conservation of a precious resource (water). Unfortunately, it has been found that increasing the solids loading reduces the rate of ethanol yield, which leads to the need for increased knowledge of the limitations in the conversion process.;One factor which has received relatively little consideration is how water organization changes within biomass materials as the solids content is increased and how this affects mass transfer resistances during saccharification. Water is essential to hydrolysis and conversion of lignocellulosic materials as it is both the medium through which enzymes diffuse to and products diffuse away from the reaction sites and a participant in the hydrolysis reaction of the glycosidic bonds of the polysaccharides. The complex structure of cellulose and the composition of the plant cell wall greatly affect ab- and adsorbed water, as water interacts both physically and chemically with components within the cell wall matrix. The goal of this study was to investigate the structuring and interactions of water in cellulose suspensions to determine how it affects saccharification and how these factors change with changing moisture content.;Nuclear magnetic resonance (NMR) spectroscopy was used to measure water structuring in bacterial cellulose suspensions at various solids contents and to compare this to water structuring in cellulose suspensions spiked with either glucose (a monosaccharide that is known to end-product inhibit beta-glucosidase) or mannose (a stereoisomer of glucose shown not to end-product inhibit beta-glucosidase). It was found that increases in solids content led to increases in the physical constraint of water in the suspensions. Moreover, the presence of either monosaccharide further increased water constraint at all solids contents to the same degree. Saccharification rates in suspensions spiked with either glucose or mannose were equally inhibited with no cellobiose detected, leading to the conclusion that decreases in saccharification efficiency are related to water constraint in cellulose suspensions as opposed to enzyme activity inhibition.;To understand if the impact of water constraint on decreases in saccharification rates was related to mass transfer resistances in the cellulose suspensions, the diffusivity of glucose (end-product of saccharification) and bovine serum albumin (BSA) (a non-cellulose-adsorbing protein of the approximate size of a typical fungal cellulase) in cellulose suspensions were assessed by NMR. Results showed decreases in intrinsic diffusivities of glucose and BSA with increasing solids content that was demonstrated to be the result of increased fluid viscosity within the cellulose suspension caused by increases in water constraint. This indicates that increased mass transfer resistances were the underlying mechanism for low sugar conversion rates under high solids conditions.;Other work discussed in this thesis includes the impact of a saccharification enhancing surfactant on water structuring and changes in water structuring within alkaline pretreated rice straw over the length of pretreatment time.