|M.Sc Student||Levy-Shalev Odelia|
|Subject||Hydrolysis of Mixed Agricultural Wastes to Sugars for|
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Carlos Dosoretz|
|Full Thesis text - in Hebrew|
Biofuels, and particularly bioethanol, produced by microbial fermentation of glucose, are considered a viable solution for the increasing energy supply demand. The most sustainable source of glucose is hydrolysis of pretreated lignocellulosic biomass by cellulases mixture. Pretreatment is required to split the crosslinking bonds of hemicellulose, separate the lignin layer and expand the cellulose crystals, allowing the enzymes to penetrate more easily. Among the most advantageous pretreatments is liquid hot water at subcritical conditions (temperature≥200°C). Water at pressure above saturation becomes acidic and an effective solvent.
In the present investigation, diluted organic acids were added to the subcritical treatment at temperatures between 100-170°C. The acids examined include formic and acetic acids, the smallest acids with the lowest pKa values, which are byproducts of thermal hydrolysis of plant biomass.
The raw materials studied included olive mill solid waste (OMSW), wheat straw (WS) and paper, separated or mixed. The experiments were conducted in a 170 ml laboratory batch reactor especially built for the research. The efficiency of the pretreatment was mainly tested by means of hydrolysis of the solid residue by cellulases. Composition analysis indicate that OMSW has good potential to be used as feedstock for producing bioethanol, although lower than WS, as it contains fewer structural carbohydrates and more lignin.
The addition of diluted acetic and formic acid to the pretreatment increased the enzymatic hydrolysis yield. Formic acid was found to be more efficient than acetic in the entire range of temperatures and concentrations tested. In all pretreatment sets a significant increase in the enzymatic utilization could be seen when pretreatment was conducted above 140 °C. Concomitant to the increase of sugar yield, the concentration of aldehyde byproducts in the liquid fraction increased with temperature and pressure, as well as concentration of organic acids. Aldehyde production was more affected by temperature than by the acidity. Nevertheless, the highest concentration detected (~1 g/L) did not surpass values reported in the literature as inhibitory of sugars fermentation to ethanol by yeast or bacteria. The change in plant cell wall structural carbohydrates tested by FTIR analysis of the solid residue of the pretreatment, displayed a similar pattern to those attained by the HPLC analysis of the liquid fraction of the pretreatment, which increased with the severity of the pretreatment conditions.
Concluding, the addition of formic acid to hydrothermal pretreatment exchanged temperature and pressure increases, resulting in a similar sugar yield during enzymatic hydrolysis.