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Permanent link (DOI): https://doi.org/10.7939/R3X410

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Optimization of biomass and lipid production in heterotrophic microalgal cultures Open Access

Descriptions

Other title
Subject/Keyword
Modeling
Heterotrophy
Biodiesel
Auxenochlorella protothecoides
Optimization
Raman Spectroscopy
Microalgae
Type of item
Thesis
Degree grantor
University of Alberta
Author or creator
De la Hoz Siegler, Hector Jr
Supervisor and department
William C. McCaffrey (Chemical and Materials Engineering)
Amos Ben-Zvi (Chemical and Materials Engineering)
Robert E. Burrell (Biomedical Engineering, Chemical and Materials Engineering)
Examining committee member and department
Robert E. Burrell (Biomedical Engineering, Chemical and Materials Engineering)
Julia M. Foght (Biological Sciences)
Sheldon J.B. Duff (Chemical and Biological Engineering, University of British Columbia)
J. Fraser Forbes (Chemical and Materials Engineering)
William C. McCaffrey (Chemical and Materials Engineering)
Amos Ben-Zvi (Chemical and Materials Engineering)
Department
Department of Chemical and Materials Engineering
Specialization

Date accepted
2011-11-24T22:52:02Z
Graduation date
2012-06
Degree
Doctor of Philosophy
Degree level
Doctoral
Abstract
Microalgae are a promising source of biofuels and other valuable chemicals. The low cell density and slow growth rate that have traditionally characterized microalgal cultures, however, have resulted in a reduced economical feasibility. To develop a sustainable microalgal process it is required to increase culture productivity, maximize production yield, and reduce production costs. To achieve these goals it is necessary to improve the current understanding of the dynamic behaviour of microalgal cultures. In this thesis, growth and oil production rates in heterotrophic cultures of Auxenochlorella protothecoides were evaluated as a function of the carbon and nitrogen source concentration. It was found that nitrogen plays a major role in controlling the productivity of microalgae. It was also shown that there exists a nitrogen source concentration at which biomass and oil production can be maximized. A mathematical model that describes the effect of nitrogen and carbon source on growth and oil production was proposed, considering the uncoupling between nitrogen uptake and growth, the possibility of luxurious uptake of nitrogen, and the time-delayed inhibitory effects caused by the transient spike in the intracellular nitrogen concentration. Using a non-linear model-based optimization approach, biomass and oil productivities were substantially increased. The use of an adaptive model predictive control strategy resulted in a 10-fold increase in the average biomass productivity and a 16-fold increase in the maximum productivity compared to batch experiments. The final cell density in the optimized culture was 144 g/L (dry weight), with 49.4%w/w oil content. The maximum lipid productivity was 20.2g/Ld, achieved during the exponential growth phase at an average cell density of 86g/L. The lipid productivity in the optimized microalgal culture was higher than any previously reported productivity value for other oleaginous microorganisms. Application of the adaptive optimization strategy to a two-stage glycerol/glucose culture resulted in an increased production yield (glucose to oil), from 0.267g/g in the optimized single-stage culture to 0.347g/g in the two-stage culture. The increased yield and productivity of the optimized cultures resulted in a largely improved economic feasibility. Composition analysis of the algal oil produced in the optimized cultures shows that the oil has a high quality as biodiesel precursor, in terms of the expected cetane number, iodine value, and cold filter plug point temperature. The higher productivity and excellent lipid profile of the optimized microalgal culture make A. protothecoides an exceptional source for biodiesel production and a potential source of single cell oil for other applications.
Language
English
DOI
doi:10.7939/R3X410
Rights
License granted by Hector Junior De la Hoz Siegler (delahozs@ualberta.ca) on 2011-11-24T22:05:07Z (GMT): Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of the above terms. The author reserves all other publication and other rights in association with the copyright in the thesis, and except as herein provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
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File title: Optimization of Biomass and Lipid Production in Heterotrophic Microalgal Cultures
File author: Hector De la Hoz Siegler
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