CO ₂ /O ₂ Recycling Through Micro Algae Culture for Life Support System in a Reduced Gravity Environment, Such as in Space 1999-01-1960

We have reported that Euglena, a photosynthetic alga, has the ability to grow in a high CO₂ atmosphere and yield great biomass due to the induction of chlorophyll biosynthesis under high CO₂ conditions. In the present study, we investigated some microalgal culturing systems for CO2 elimination and O₂ regeneration in closed air on the ground by using the photosynthetic alga, Euglena gracilis. z.

In the first part of our experiments, we focused on the effects of CO2 and light intensity in the present culture system. We investigated to determine the optimum culture conditions for a microalgal culture system that functions effectively in the controlled ecological life support systems (CELSS). We determined the maximum elimination rate under a high concentration of CO₂ with stirring of the supply gas by bubbling. We found that the maximum CO₂ elimination rate or gas exchange performance under a 10 % concentration of CO₂ was about 2.3 times higher than its low concentration of CO₂ (0.04 %). The results suggest that the CO₂ concentration in the supply gas rate limits the algal system performance. In the second part of present experiments, we developed a bioregenerative system for converting CO₂ to O₂ which uses two functional membranes because centrifuge did not seem good for a micro algal culturing system under low gravity conditions. As ordinary atmospheric air contains about 0.04 % CO₂, we introduced two different modules; one was a selective gas / water separation module which is able to separate CO₂ specifically from the atmospheric air, and the other was a non-selective gas/water separation module which supplies O₂ rich gas in the chamber after passing through the photobioreacti CO₂ generator. At present, we conclude that introduction of selective membrane for the separation of O₂ and CO₂ is necessary and efficient under microgravity conditions.