Water Recovery from Human Metabolic Waste: System Design, Analysis, and Preliminary Results

Paragon Space Development Corporation is developing a system to recover water from human metabolic waste, i.e. feces, in support of NASA's Water Recovery Technology Roadmap. Through a NASA Phase II Small Business Innovation Research (SBIR) award, the Separation Technology of On-Orbit Liquid and Excrement (STOOLE) system uses heated air to drive recoverable water off of fecal deposits through gas permeable bags. Drying and stabilization of feces can reduce odor generation and prevent microbial proliferation if the water activity level is less than 0.6. In use on a spacecraft, water vapor would be returned to cabin air through a series of filtration and ionomer membrane distillation steps and collected by the existing condensing heat exchangers. The system is designed to recover >80% of the available water content, with built-in modularity to facilitate compatibility with existing waste collection hardware (i.e. the Universal Waste Management System (UWMS)). The cost for recovering fecal water in terms of mass, power, volume, and crew time equivalents must not outweigh the benefits of the mass savings obtained from water recovery over the balance of a mission, for example. This paper will discuss the progress to date on system design and analysis, materials selection, fecal simulant development, and system component testing.