Space exploration will require new life support systems to support the crew on journeys lasting from a few days to several weeks, or longer. These systems should also be designed to reduce the mass required to keep humans alive in space. Water accounts for about 80 percent of the daily mass intake required to keep a person alive. As a result, recycling water offers a high return on investment for space life support. Water recycling can also increase mission safety by providing an emergency supply of drinking water, where another supply is exhausted or contaminated.

These technologies also increase safety by providing a lightweight backup to stored supplies, and they allow astronauts to meet daily drinking water requirements by recycling the water contained in their own urine. They also convert urine into concentrated brine that is biologically stable and non-threatening, and can be safely stored onboard. This approach eliminates the need to have a dedicated vent to dump urine overboard.

These needs are met by a system that provides a contaminant treatment pouch, referred to as a “urine cell” or “contaminant cell,” that converts urine or another liquid containing contaminants into a fortified drink, engineered to meet human hydration, electrolyte, and caloric requirements, using a variant of forward osmosis (FO) to draw water from a urine container into the concentrated fortified drink as part of a recycling stage. An activated carbon pretreatment removes most organic molecules. Salinity of the initial liquid mix (urine plus other) is synergistically used to enhance the precipitation of organic molecules so that activated carbon can remove most of the organics. A functional osmotic bag is then used to remove inorganic contaminants. If a contaminant is processed for which the saline content is different than optimal for precipitating organic molecules, the saline content of the liquid should be adjusted toward the optimal value for that contaminant.

A first urine treatment method converts urine into a fortified sports drink, resembling Gatorade, using a first urine cell. A membrane filter that is hydrophilic allows water to diffuse through the filter but blocks most contaminants using a micropore construction. Water is drawn through the membrane by a forward osmotic pressure differential, generated by the liquid feed, sugars, and electrolytes contained in a concentrated sports drink, which is positioned on the product (output) side of the membrane. Water, initially contained in urine, diffuses through the membrane to approximately balance the concentration gradient. As a result, the sports drink will become diluted and the urine will become concentrated. The maximum number of urine recycling sessions is about ten. The process is a modification of a process used in a water treatment cell from Hydration Technologies X-Pack.

A second urine treatment method uses osmotic distillation and a hydrophobic, microporous membrane filter, with a product (output) side exposed to a second liquid phase that is capable of absorbing wastewater that is presented on the input side of the filter. The method is sometimes referred to as isothermal membrane distillation and is driven by a vapor pressure gradient rather than by a temperature gradient.

This work was done by Michael T. Flynn of Ames Research Center and Sherwin J. Gormly of the National Space Grant Foundation. ARC-15890-1

NASA Tech Briefs Magazine

This article first appeared in the November, 2012 issue of NASA Tech Briefs Magazine.

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