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High consistency enzymatic hydrolysis of lignocellulose Qin, Wenjuan

Abstract

The work described in this thesis focused on the development of a practical, high consistency hydrolysis and fermentation processes utilizing existing pulp mill equipment. Carrying out enzymatic hydrolysis at high substrate loading provided a practical means of reducing the overall cost of a lignocellulose to ethanol bioconversion process. A laboratory peg mixer was used to carry out high consistency hydrolysis of several lignocellulosic substrate including an unbleached hardwood pulp (UBHW), an unbleached softwood pulp (UBSW), and an organosolv pretreated poplar (OPP) pulp. Enzymatic hydrolysis of OPP for 48 hours resulted in a hydrolysate with a glucose content of 158 g/L. This is among the highest glucose concentration reported for the enzymatic hydrolysis of lignocellulosic substrates. The fermentation of UBHW and OPP hydrolysates with high glucose content led to high ethanol concentrations in the final fermentation broth (50.4 and 63.1 g/L, respectively). These values were again as high as any values reported previously in the literature. To overcome end-product inhibition caused by the high glucose concentration resulting from hydrolysis at high substrate concentration, a new hydrolysis and fermentation configuration, (liquefaction followed by simultaneous saccharification and fermentation (LSSF)), was developed and evaluated using the OPP substrate. Applying LSSF led to a production of 63 g/L ethanol from OPP. The influence of enzyme loading and β-glucosidase addition on ethanol yield from the LSSF process was also investigated. It was found that, at higher enzyme loading (10FPU or higher), the ethanol production from LSSF was superior to that of the SHF process. It was apparent that the LSSF process could significantly reduce end-product inhibition when compared to a Separate Hydrolysis and Fermentation (SHF) process. It was also apparent that β-glucosidase addition was necessary to achieve efficient ethanol production when using the LSSF process. A 10CBU β-glucosidase supplement was enough for the effective conversion of the 20% consistency OPP by LSSF. The rheological property change of the different substrates at the liquefaction stage was also examined using the rheometer technique. The use of a fed-batch hydrolysis process to further improve the high consistency hydrolysis efficiency was also assessed.

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