Quantitative Study of Stoichiometric Proton Imbalance in Phototrophic Algal Growth

Open Access
Wang, Jun
Graduate Program:
Chemical Engineering
Master of Science
Document Type:
Master Thesis
Date of Defense:
April 25, 2013
Committee Members:
  • Wayne Roger Curtis, Thesis Advisor
  • Andrew Zydney, Thesis Advisor
  • Antonios Armaou, Thesis Advisor
  • Janna Kay Maranas, Thesis Advisor
  • algae
  • biofuel
  • pH
  • process control
  • nitrogen
The high production of algae based biofuel requires high density of algae culture. One of the important issues associated with high density algae cultivation is pH instability, which is due to inherent proton imbalance in algae metabolism. Among different nitrogen sources in typical algae culture media, nitrate and ammonium lead to alkalinization and acidification of the media, respectively, as they are consumed. Compared to other pH control strategies such as buffering or acid-base addition, the metabolic control of pH based on feeding different nitrogen sources provides a potential pH control strategy that is technically feasible in large scale outdoor biofuel production. To accomplish this, a fed-batch nutrient feeding strategy would need to be adopted in a model-based pH control system. Due to the current lack of understanding of the magnitude of the stoichiometric pH imbalance under different nitrogen sources, this MS thesis presents a quantitative assessment of the proton imbalance for micro algae (Chlorella) grown on different nitrogen sources. Our results give tentative experimental values for the pH imbalance associated with nitrate and ammonium media, which can be used as initial parameters in a pH control system based on stoichiometric utilization of nitrogen during algae growth. This thesis also presents a preliminary interpretation of these results as they relate to the biology of nitrogen uptake and metabolism as well as the chemistry associated with media buffering.