Bioregeneration in space.

ESA has been studying a small-scale bioregenerative system to support long-term biological experiments on-board spacecraft with oxygen, water, and food. Core component of this system is a special photo-bioreactor in which a maltose-producing strain of the green alga Chlorella is cultivated. In initial experiments this bioreactor has been tested, and the physiology of Chlorella has been studied. The optimal conditions for CO2 to O2 conversion and maltose production have been determined, and the possibility of controlling the culture so as to match the needs of the consumer has been established. A microgravity-compatible photo-bioreactor, and a maltose separator have been developed and are functioning on the ground according to the design specifications. Tests in weightlessness will have to be performed in the future. The components are to be integrated to a complete bioregenerative life support system, which will then be subjected to extensive testing. The EXEMSI project afforded an opportunity to study the mutual influence of a Chlorella culture and real biological oxygen consumers, the four crew members in the laboratory module of the isolation facility. Chlorella 241.80 was batch cultured in an airlift bioreactor by the crew for 25 days with air aspirated from the module. The crew members determined pH and cell density in samples withdrawn from the culture. Microscopic observations showed no evidence of contamination of the culture by other organisms. Growth rates were smaller than those observed in laboratory conditions. This is attributed to the relatively low average CO2 concentration in the module atmosphere: 0.1% against 0.5% in the air supply during the laboratory experiments. The data show no evidence of trace contaminant accumulation in the Chlorella culture. The results are encouraging and suggest the value of further simulated operational testing of the system.