Date of Award

Fall 1-1-2020

Degree Type

Thesis

Degree Name

Master of Science In Chemical Engineering Degree

Department

Chemical And Biomedical Engineering

First Advisor

Belovich, Joanne

Second Advisor

Dr. Jorge Gatica

Third Advisor

Dr. Chandra Kothapalli

Abstract

Microalgae are abundant unicellular photosynthetic organisms with more than 200,000 species. They are more efficient in harvesting solar energy than land-based plants with green microalgae having more than ten times higher biodiesel productivity than the next best land-based crop. Their ability to grow in harsh environments, non-agricultural lands, and make use of wastewater, and the diversity of the products that can be extracted from them, which include cosmetics, pharmaceuticals, food supplements, biofuels, and many others, gives them the potential to replace fossil fuels and revolutionize the biotech industry. In order to move onto large scale production, first, the growth rate of the cell culture must be increased, which requires screening of promising species, studying their growth kinetics, and selecting their most suitable environment. Second, microalgae use their internal energy reservoirs (lipid bodies) during dark periods; nighttime biomass loss must be prevented. In this study, we analyzed the effect of light intensity on the growth of Chlorella sorokiniana, a promising species for biofuel production. We constructed a growth model that accurately predicts the growth response of the cell culture to varying irradiance conditions and photoperiods. We incorporated the concept of Monod kinetics into our model and quantified the effect of light intensity on biomass accumulation under lightlimiting conditions. We determined that the empirically measured maximum growth rate v parameter has a value of 0.20 h-1 which is limited by the maximum photosynthetic rate. Additionally, we determined the Monod saturation constant to be 238 |imol s-1 m-2. We found that biomass loss rate due to respiration and other metabolic activities peaked during the day (8.7x10-3 h-1), and was constant during nighttime (1.8x10-3 h-1). We determined that 5% of the biomass gained during the 16-hour day period was lost during the following 8-hour dark period, which lead to a 16% lower biomass yield when compared to a continuously illuminated culture after nine days of cultivation at a constant temperature of 30°C in a well-mixed five-liter photobioreactor. Finally, we illustrated that illuminating the dark period with low-consumption red LEDs will prevent biomass loss and enhance cell replication.

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