Extraction of Potable Water from Urine for Space Applications

by Peter J. Holland, US Air Force Acad, United States,
Donald M. Bird, US Air Force Acad, United States,
Carolyn L. Miller, US Air Force Acad, United States,



Document Type: Proceeding Paper

Part of: Engineering, Construction, and Operations in Space III

Abstract: A regenerative technology capable of managing water and wastewater on-board long-term manned space platforms is essential if the Bush Administration's Space Exploration Initiative (SEI) objectives are to be met. The viability of one such wastewater regenerative technology is currently being investigated at the United States Air Force Academy, Colorado by an interdisciplinary faculty-cadet research team. The technology is based on the principles of freeze-drying or 'lyophilization' using the abundant and available vacuum and cold of space. In much the same fashion as coffee manufacturers extract moisture from ground coffee, moisture or water vapor can be extracted from frozen wastewater by sublimation, condensed on a cold surface and recycled to meet potable water requirements. In this research, human urine was frozen in liquid nitrogen, subjected to 15 micron of mercury vacuum for 14-24 hours, and recovered on a cold probe at a temperature of -90°C. The resulting ice was aseptically removed, melted, weighed, and analyzed for solids content, ammonia-nitrogen concentration, and bacterial presence. Several product water samples were passed through a 0.2 micron filter prior to analysis. The total solids, total suspended solids, and total dissolved solids contents in unfiltered lyophilized product water measured 50.5 mg/L, 12.5 mg/L, and 38.0 mg/L, respectively. The total solids, total suspended solids, and total dissolved solids contents in filtered lyophilized product water measured 34.7 mg/L, 1.7 mg/L, and 33.0 mg/L, respectively. The ammonia-nitrogen levels in the unfiltered and filtered product water measured 1.5 mg/L and 2.2 mg/L, respectively. E. Coli was not detected in the unfiltered or filtered product water lyophilized from either the raw urine or the 3.0 × 107 colony forming units (CFU)/mL spiked urine samples. These results compared favorably with NASA's proposed water quality requirements for the Space Station Freedom, and published data on the treatment of urine using reverse osmosis and freeze-crystallization technologies. Future research will involve validating the results of this screening study, as well as expanding upon the lyophilized product water's analytical parameters, lyophilizing and testing other wastewaters, and initiating process design for harnessing the vacuum and cold of space aboard space platforms.

Subject Headings: Water quality | Dissolved solids | Space life support systems | Space exploration | Drinking water | Wastewater management | Filters | Freezing | Solid mechanics | North America | United States | Colorado

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