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Disinfection of Spacecraft Potable Water Systems by Passivation with Ionic SilverMicrobial growth is common on wetted surfaces in spacecraft environmental control and life support systems despite the use of chemical and physical disinfection methods. Advanced control technologies are needed to limit microorganisms and increase the reliability of life support systems required for long-duration human missions. Silver ions and compounds are widely used as antimicrobial agents for medical applications and continue to be used as a residual biocide in some spacecraft water systems. The National Aeronautics and Space Administration (NASA) has identified silver fluoride for use in the potable water system on the next generation spacecraft. Due to ionic interactions between silver fluoride in solution and wetted metallic surfaces, ionic silver is rapidly depleted from solution and loses its antimicrobial efficacy over time. This report describes research to prolong the antimicrobial efficacy of ionic silver by maintaining its solubility. Three types of metal coupons (lnconel 718, Stainless Steel 316, and Titanium 6AI-4V) used in spacecraft potable water systems were exposed to either a continuous flow of water amended with 0.4 mg/L ionic silver fluoride or to a static, pre-treatment passivation in 50 mg/L ionic silver fluoride with or without a surface oxidation pre-treatment. Coupons were then challenged in a high-shear, CDC bioreactor (BioSurface Technologies) by exposure to six bacteria previously isolated from spacecraft potable water systems. Continuous exposure to 0.4 mg/L ionic silver over the course of 24 hours during the flow phase resulted in a >7-log reduction. The residual effect of a 24-hour passivation treatment in 50 mg/L of ionic silver resulted in a >3-log reduction, whereas a two-week treatment resulted in a >4-log reduction. Results indicate that 0.4 mg/L ionic silver is an effective biocide against many bacteria and that a prepassivation of metal surfaces with silver can provide additional microbial control.
Document ID
20110014435
Document Type
Conference Paper
Authors
Birmele, Michele N. (NASA Kennedy Space Center Cocoa Beach, FL, United States)
McCoy, LaShelle e. (NASA Kennedy Space Center Cocoa Beach, FL, United States)
Roberts, Michael S. (NASA Kennedy Space Center Cocoa Beach, FL, United States)
Date Acquired
August 25, 2013
Publication Date
July 17, 2011
Subject Category
Man/System Technology and Life Support
Report/Patent Number
KSC-2011-153
Meeting Information
41st International Conference of Environmental Systems(Portland, OR)
Funding Number(s)
CONTRACT_GRANT: NNK11EA08C
CONTRACT_GRANT: NAS10-02001
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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