1995-07-01

Further Characterization and Multifiltration Treatment of Shuttle Humidity Condensate 951685

On the International Space Station (ISS), humidity condensate will be collected from the atmosphere and treated by multifiltration to produce potable water for use by the crews. Ground-based development tests have demonstrated that multifiltration beds filled with a series of ion-exchange resins and activated carbons can remove many inorganic and organic contaminants effectively from wastewaters. As a precursor to the use of this technology on the ISS, a demonstration of multifiltration treatment under microgravity conditions was undertaken. On the Space Shuttle, humidity condensate from cabin air is recovered in the atmosphere revitalization system, then stored and periodically vented to space vacuum. A Shuttle Condensate Adsorption Device (SCAD) containing sorbent materials similar to those planned for use on the ISS was developed and flown on STS-68 as a continuation of DSO 317, which was flown initially on STS-45 and STS-47. The experiment investigated the effectiveness of this device for in-flight treatment of Shuttle humidity condensate for removing organic and inorganic contaminants. Ground-based analyses of samples returned from the STS-68 mission showed that as much as 77% of the organic carbon in Shuttle condensate was removed by the SCAD. Concentrations of total organic acids (mainly acetic, formic, lactic, and propionic acids) and of total semivolatile organic compounds in the SCAD effluent were consistently reduced by 88% or more. The SCAD sorbents also effectively reduced concentrations of anions, cations, and trace metals to part-per-billion levels; the most notable of these were zinc, silicon, and ammonium, whose levels in the untreated condensate were as high as 28, 15, and 12 mg/L, respectively. Concentrations of ethanol, propanol, butanol, formaldehyde, and propylene glycol (1,2-propanediol) were reduced less effectively by the SCAD. Methanol levels did not seem to be reduced by treatment. By the ninth day of the flight, the throughput had exceeded the design specification of 3 liters and the amount of total organic carbon in the SCAD effluent was greater than that of the untreated condensate (a chromatographic effect). Analysis of specific organic compounds indicated that alcohols, specifically ethanol and propanol, made up a significant portion of this effect.

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