A Continuous Bioreactor to Study the Persistence of Extracellular Biofuel Candidate Molecules in a Non-axenic Algae Culture

Open Access
Author:
Taylor, Christine Alana
Area of Honors:
Chemical Engineering
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Wayne Roger Curtis, Thesis Supervisor
  • Enrique Daniel Gomez, Honors Advisor
Keywords:
  • weed algae
  • product degradation
  • chemostat
Abstract:
Reverse engineering refers to an assessment of the successful outcome by first determining if it is able to persist in a non-axenic environment. In other words, our hypothesis is that many potential fuel candidates will be heterotrophically consumed by the surrounding microbial population in a commercial non-axenic production environment. Organisms can be genetically modified to secrete different biofuels; however, if these biofuels cannot withstand the common non-axenic and aerobic conditions of an industrial algae production facility, then they will not be successful on a commercial scale. A 30 L continuous culture of Chlorella vulgaris was maintained in non-sterile conditions to provide a realistic algae production environment. The “smart pond” was maintained as a repeated semi-batch process and was studied to better understand the pH fluctuations that are mediated by the CO2-bicarbonate equilibrium. A model was created to determine the stability of the pond if a “weed algae” with a 20% higher yield (to simulate competitive growth advantage) was to enter the system; the model predicted that the pond would remain stable indefinitely with the addition of 50 mL of axenic C. vulgaris with an OD equal to 5 (1.73 x 1010 cells). This simulation suggests that the addition of much smaller cell numbers (on the order of 108 cells) would be sufficient to maintain a stable “smart pond”. Due to limited time, degradation studies were performed in axenic and non-axenic C. vulgaris cultures only using the biofuel feedstock molecules sucrose and glucose, as these have also been proposed to be secreted by genetically modified organisms. The degradation of both feedstocks was higher in a non-axenic C. vulgaris culture compared to an axenic culture. Future work will conduct degradation experiments with biofuel molecules such as biobutanol and ethanol. These degradation rates will be compared to that of botryococcene, which is hypothesized to have a uniquely low degradation rate due to its natural extra-cellular persistence in non-sterile environments.