BAE Graduate Student Seminar
Thursday, May 29, 2014
9-10 am, 2045 BAINER HALL
Topic: Development of Optimal Enzymatic and
Microbial Conversion Systems for Biofuel Production
Presenter: Natthiporn Aramrueang
PhD Candidate, Biological Systems Engineering
University of California, Davis
Abstract
The increase in demand for fuels, along with the concerns over the depletion of fossil fuels and the environmental problems associated with the use of the petroleum-based fuels, has driven the exploitation of clean and renewable energy. Through a collaboration project with Mendota Bioenergy LLC to produce advanced biofuel from sugar beets and other locally grown crops in the Central Valley of California through a demonstration and commercial-scale biorefineries, the present study focused on the investigation of selected potential biomass as biofuel feedstock and development of bioconversion systems for sustainable biofuel production. For an efficient biomass-to-biofuel conversion process, three important steps, which are central to this research, must be considered: feedstock characterization, enzymatic hydrolysis of the feedstock, and the bioconversion process.
Physical characteristics and composition were analyzed for the important crops and residues available in Central Valley of California, including four varieties of sugar beet, melons, tomato, Jose tall wheatgrass, wheat hay, and wheat straw. Melons and tomatoes are those discarded by the growers or processors due to poor quality. The mass-based ethanol potential of each feedstock was determined based on the composition. Sugar beet root shows a high ethanol yield (127 L/metric ton on a wet basis or 591 L/ metric ton on a dry basis), mainly resulted from the high sucrose content (71% d.b.). Sugar-containing biomass, such as melons and tomato, shows high soluble sugar content ranging 53-69% and 42 % on dry basis, respectively. Lignocellulosic biomass, including Jose Tall wheatgrass and wheat straw, are composed primarily of cellulose (27-39% d.b.) and hemicellulose (26-30% d.b.). The ethanol yields from these materials range from 470 to 533 L ethanol/metric ton d.b.
As remaining unused in great quantities during the large production of sugar beet as a sugar and energy crop, sugar beet leaves was studied as a potential feedstock for the production of biofuel and valuable products. The enzymatic hydrolysis of sugar beet leaves was optimized for the production of fermentable compounds. Response surface methodology was used to study the effects of enzyme loadings on the hydrolysis of sugar beet leaves at solids loading (10% TS), using a mix of cellulases, hemicellulases, and pectinases. A maximum sugar yield of 80% was achieved after 48h of hydrolysis. The statistical analyses show that cellulases and pectinases are important enzymes for the hydrolysis of sugar beet leaves.
The last part of the study investigated biogas production through the anaerobic digestion of microalgae as they have been received much attention as another potential biofuel feedstock. Anaerobic digestion of Spirulina (Arthrospira platensis) was conducted to investigate the biodegradability and conversion kinetics. The maximum biogas and methane yields for Spirulina are 0.514 L/g VS and 0.360 L CH4/g VS, respectively. The methane content of the biogas is 68%. Continuous digestion experiments in CSTR were conducted over one year to study the effects of hydraulic retention time (HRT) and organic loading rate (OLR). From the varying HRT (10-25 d) and OLR (1.0-4.0 g VS/L/d), biogas and methane yields were in the ranges of 0.276-0.502 L/ g VS and 0.163-0.342 L CH4/g VS, respectively. Methane content was 59-70% of the biogas. Ammonia inhibition and the accumulation of volatile fatty acids (VFA) were observed at high OLR. A novel mathematical model was developed for relating the kinetics degradation of the substrate obtained from batch digestion for the prediction of methane yield during a continuous process, in relation to HRT. The model can apply to the use of a CSTR for a digestion of high-protein organic materials such as manure and meat processing wastes.
Coffee and cookies will be served.
