A Prototype Torrefaction Processing Unit (TPU) for Human Solid Waste in Space

This paper describes work on the development of a Torrefaction Processing Unit (TPU) that can be used to recover moisture and sterilize feces, resulting in a stable, odor-free solid product that can be easily stored or recycled. This TPU is designed to be compatible with the Universal Waste Management System (UWMS), now under development by NASA. A stand-alone TPU could be used to treat the waste canister from the UWMS, thus allowing the waste canister to be reused and significantly reducing the number of canisters required on board. The prototype design process included an initial trade-off study that examined the advantages and disadvantages of full integration of the TPU with the UWMS. In the first scenario, the TPU would be incorporated into the base of the UWMS, where the canister would be heated in-situ. In the second scenario, the TPU would be a standalone unit that could be operated independently of the UWMS. While the former approach has the advantage of reducing the overall footprint, it would be more complex and would likely interrupt operation of the UWMS if operated in a batch mode. Consequently, the latter approach of an independent TPU has been retained. In this case, two major design approaches were considered, one which incorporated a Gas Circulation Reactor (GCR) and another which incorporates an In-situ Compaction Reactor (ICR). These were compared based on several factors, including energy consumption, temperature uniformity, crew labor, cleanliness, and consumables.