Development of a Testbed for Flow-Through Measurements of Algal Metabolism Under Altered Pressure for Bioregenerative Life Support Applications

The utilization of algae is a widespread concept for bioregenerative life support systems in human spaceflight. Algae have the potential to combine the functions of air revitalization, wastewater treatment, and food production via photosynthesis. The potential benefits of using algae include high reliability, reduced mass, and psychological benefits to the crew. Due to the fast growth rate and ease of culturing, Chlorella vulgaris is well documented in terms of optimal growth parameters, such as carbon dioxide or oxygen concentration, growth medium, temperature, as well as light cycle, spectrum, and intensity. However, the feasibility of algal photobioreactors for air revitalization, wastewater treatment, and food production under relevant spaceflight environments is not fully assessed. In particular, algal growth under NASA’s proposed exploration atmosphere of 8.2 psia and 34 % oxygen for long-duration human spaceflight missions has not been characterized. Therefore, a flow-through photobioreactor that is capable of maintaining specified growth conditions for Chlorella vulgaris and controlling the pressure in the reactor between 56.5 and 101.3 kPa (8.2 and 14.7 psia) was developed and is presented in this paper. The sizing process of the small scale photobioreactor for gaining accurate oxygen and carbon dioxide measurements is described. Additionally, challenges, such as leak rates, measurement resolution, and water temperature alternating the solubility of carbon dioxide and oxygen, are discussed. In conclusion, the adaptations to more typical state-of-the-art, environmentally-open reactor designs, necessary to meet the minimal leak rate requirements for measuring the gas exchanges, are summarized. Preliminary metabolic measurements from the algal photobioreactor testbed are presented. Future characterization studies, using this testbed design, can lead to a better understanding of algal performance and more accurate system analysis for future life support system designs.