Electronic Theses and Dissertations

Title

Preprocessing of Biomass Using Mechanical, Chemical and Microbial Techniques

Date of Award

2012

Document Type

Dissertation

Degree Name

Ph.D. in Engineering Science

First Advisor

Clint Williford

Second Advisor

Colin R. Jackson

Third Advisor

John O'Haver

Abstract

Biomass-derived fuels have acquired a lot of attention recently due to increasing emphasis on energy independence, efforts to utilize abundance of green resources and mitigation of greenhouse gas emissions. Grasses, agricultural residues, animal residues and waste, used oils, etc., can be used as starting materials in the production of biofuels. Various preprocessing techniques used in the preprocessing of biomass, such as microbial preprocessing, mechanical preprocessing and chemical pretreatment, are used for enhancing the digestibility of biomass to sugars for ethanol production. In this work, studies were conducted to improve the microbial, chemical and mechanical preprocessing of switch grass by decreasing the treatment time, optimizing the pretreatment temperature and enzyme requirements, and by developing a mechanical method to identify the heterogeneous fractions of switch grass. Switch grass was preprocessed with the fungus Phanerochaete chrysosporium and enzyme profiles were determined for various cellulase and lignin related enzymes. The enzyme profiles peaked at the 7th day during the 28 day treatment. Following the enzyme profile results, a seven day enzyme hydrolysis of switch grass resulted in a 5 % w/w increase in total sugar yields and 5 % increase in glucan % w/w by composition, and decreased the treatment time fourfold when compared to previous literature. A mechanical size separation method was developed for switch grass to identify the heterogeneous fractions in bulk and the pretreatment and enzyme requirements were estimated for individual fractions using design of experiments. This study demonstrated that each fraction had different composition in terms of glucan, xylan and lignin, and had different pretreatment and enzyme requirements for hydrolysis. The recalcitrant fraction, <1 mm, was identified based on greater pretreatment and enzyme requirements, lower glucose yields and higher crystallinity, suggesting biomass enrichment by about 10 % through its elimination from unpartitioned switch grass. Microbial preprocessing on size separated fractions of switch grass showed higher enzyme activity for >1 mm size fraction. The activity profiles varied by enzyme and by peak times during a 12 day preprocessing period for each of the fractions. Size separated fractions had lower glucose yields compared to the unpartitioned switch grass after microbial preprocessing. However, preprocessed samples had higher glucose yield compared to the raw samples for all fractions. The studies, improved the glucose yield of switch grass through various preprocessing techniques, decreased the microbial preprocessing time, and identified the recalcitrant fraction of switch grass.

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