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Thermophilic aerobic digestion was investigated as a potential waste treatment technology for biodegradable wastes generated in a long-term closed eco-system. The overall objectives of this research were to contribute to a regenerable closed-loop system for food production and water, air and waste treatment, while also minimizing the mass, volume, power, cooling and crewtime needs of the overall system. Biological treatment becomes more feasible due to resupply constraints with longer mission scenarios. The primary objectives of this research included the evaluation of the system, including effects of influent solids loadings, hydraulic retention time, oxygen transfer, and the influence of operational parameters such as pH, ORP, and temperature. Investigation into the effect of mechanical changes in the system on oxygen transfer was evaluated.

The application of biological treatment to solid waste is very promising to facilitate recycling of water, carbon, and nutrients and to reduce the resupply needs of long-term crewed space missions. Degradation of biodegradable solid wastes generated during such a mission is under investigation as part of the NASA Center of Research and Training (NSCORT) at Purdue University. Processing in the solids thermophilic aerobic reactor (STAR) involves the use of high temperature micro-aerobic slurry conditions to degrade solid wastes, enabling the recycling of water, carbon, and nutrients for further downstream uses. Related research presently underway includes technical development and optimization of STAR operations as well as a complementary evaluation of post-STAR processing for gas-stream purification, water recovery by condensate purification, and residuals utilization for both mushroom growth media and nutritional support for fish growth.