The regulation of CO2 levels in a BLSS by controlling the solid waste treatment unit

• Optimal fermentation conditions of the solid waste bio-convertor were determined.
• The output CO2 and the fermentation temperature were in a positive correlation.
• The gas balance in BLSS can be regulated by changing the fermentation temperature.

A bioregenerative life support system (BLSS) is an artificial closed ecosystem which provides basic human life support for long-duration and far-distance space activities such as lunar bases. “Lunar Palace 1”, an experimental facility, was constructed by our team for the integration research of the key technologies in BLSS, and then a continuous 105-day closed integrative BLSS experiment was carried out in “Lunar Palace 1”(Stage I) successfully last year. In such a system, O2 produced by higher plants is supplied for the breathing of the crew, as well as the respiration of microorganisms which decompose the solid wastes such as inedible plant biomass and human wastes, while CO2 produced by the crew and microorganisms is provided for plants to grow. In the system, an excessively high CO2 level can affect plant growth and may harm human health, however, if the CO2 level is too low, plant growth may also be inhibited. Thus, keeping the balance between CO2 and O2 levels is essential to the gas regulation in the system, and is one of the key points for the operation stability of the system. In this study, an efficient and controllable solid waste bio-convertor was built based on the microbial fermentation in “Lunar Palace 1”, and the CO2 generation of the bio-convertor under the optimum fermentation conditions in the 105-day airtight experiment was monitored. Moreover, the changes of CO2 production along with increasing or reducing the temperature of the bio-convertor from 33 to 45 °C (or from 45 to 33 °C) were also investigated, and a positive correlation between the CO2 output and the fermentation temperature was obtained accordingly. Therefore, the CO2 production can be adjusted effectively by changing the temperature of the bio-convertor, which implies that it is feasible to regulate the balance between the CO2 and O2 concentrations in BLSS by controlling the fermentation conditions of the solid waste treatment unit. The results of this study could lay a foundation for the following researches conducted in “Lunar Palace 1”.