Date of Award
Doctor of Philosophy
Food Science and Human Nutrition
This body of research focuses on two major areas related to microalgae-based fuel and chemical production. The first area is to produce algal lipid by utilizing fractionated pyrolytic bio-oil as feedstocks. The second area is the use of agriculture by-products as substrates for fermentative production of eicosapentaenoic acid (EPA).
The hypothesis of the first part of this work was that fractionated bio-oil can be used as feedstock for lipid-based fuel production by the microalga Chlamydomonas reinhardtii. The acetic acid-rich fraction of bio-oil derived from fast pyrolysis of softwood contains myriads of other compounds, some of which are toxic to C. reinhardtii. To enhance the fermentability of the acetic acid-rich bio-oil fraction by microalgae, activated carbon treatment was used to reduce the toxicity of this bio-oil fraction, while metabolic evolution was used to enhance the toxicity tolerance of the microalgae strain. Combining activated carbon treatment and using adapted algal strains through metabolic evolution resulted in significant improvement to algal growth performance on acetic acid-rich bio-oil fraction. A viable approach was discovered to produce fuels and chemicals from lignocellulosic biomass through the hybrid (fast pyrolysis-fermentation) process.
The hypothesis of the second part of this work was that agriculture by-products, including rendered animal proteins and thin stillage derived from corn ethanol production, can be used as nutritional sources for microbial growth and EPA (omega-3 fatty acid) synthesis. Rendered animal proteins were hydrolyzed into small peptides and free amino acids to facilitate nutrient absorption by the microalga Schizochytrium limacinum and the fungus Pythium irregulare. The utilities of using protein hydrolysates for growing microorganisms depended on the hydrolysis method used and the type of microorganism. The enzymatic hydrolysates supported better cell growth performance than did alkali hydrolysates. P. irregulare displayed better overall growth performance on the experimental hydrolysates compared to S. limacinum. Under selected conditions for P. irregulare culture, cell growth, lipid synthesis, and omega-3 fatty acid production were similar to cultures using commercial yeast extract.
Thin stillage from dry-grind ethanol production contained various compounds that were ideal for fungal growth. Thin stillage concentration and temperature played important roles in fungal growth and EPA production. When 50% thin stillage was used in a stepwise temperature shift culture process, the cell density reached 23 g/L at day 9 with EPA yield and productivity of 243 mg/L and 27 mg/L·day, respectively. The fungal culture also generated a nutrient-depleted liquid by removing organic compounds from the raw thin stillage.
Liang, Yi, "Lipid products from agriculture by-products and pyrolytic oil" (2012). Graduate Theses and Dissertations. 12817.