1992-07-01

Recovering Potable Water from Wastewater in Space Platforms by Lyophilization 921323

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 environment 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 and a NASA standard wastewater cocktail were characterized, frozen, subjected to a vacuum of 0-15 microns of mercury for 14-24 hours, and recovered on a condensation surface controlled at a temperature of -55°C. The resulting ice plug was aseptically removed, melted, weighed, and analyzed for bacterial presence, pH, solids content, and ammonia-nitrogen concentrations. The results showed that non-encapsulated Escherichia coli and encapsulated Klebsiella pneumoniae did not survive the lyophilization process. Bacillus subtilis, an endospore-forming bacterium, did survive although its viability was reduced by over 99%. These bacterial strains were chosen due to their presence in human urinary tract infections (UTIs) and their use as water quality indicators. Additionally, they are also the best representative of the non-encapsulated, encapsulated, and endospore-forming bacteria. The pH of lyophilized human urine and wastewater cocktail measured 6.7 and 6.6, respectively, while their total solids (TS), suspended solids (TSS), and dissolved solids (TDS) concentrations were all less than 50 mg/L. This represents greater than 99% reduction of the urine's and 96% reduction of the cocktail's initial TS, TSS, and TDS concentrations. Fixed and volatile solids fractions also exhibited low concentrations, many below the experiment's predetermined detection level of 10 mg/L. Ammonia-nitrogen levels in the urine's and cocktail's lyophilized product waters were reduced from 651 mg/L and 459 mg/L to 2.2 mg/L and 0.3 mg/L, respectively. Lyophilization reduced the urine's and cocktail's initial ammonia-nitrogen feed concentrations by over 99% as well. These results compared favorably with EPA's current drinking water standards and NASA's proposed water quality requirements for the Space Station Freedom.

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