P11: Disinfection of Spacecraft Potable Water Systems with Ultraviolet Light Emitting Diodes, Titanium Dioxide, and Ionic Silver

The National Aeronautics and Space Administration (NASA) seeks technology to improve microbial control in order to maintain life support systems and increase reliability during long duration missions. This research describes proof-of-concept testing of a commercial, high power ultraviolet-A light emitting diode (UV-A LED) (250mW λ_365nm) for excitation of the photocatalyst titanium dioxide as a point-of-use disinfection device in a potable water system. In order to address the lack of residual disinfection effect from the UV light, the efficacy of ionic silver as a biocide was also tested. Three types of metal coupons made of materials previously 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. Coupons were then challenged in a high-shear CDC reactor by exposure to six bacteria previously isolated from spacecraft potable water systems. UV-A LEDs with anatase titanium dioxide generated a >7-log reduction of the challenge bacteria in <180 minutes of contact time.  In the absence of UV-A and titanium dioxide, continuous exposure to 0.4 mg/L ionic silver over the course of 48 hours also 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. With continued advancement in the manufacture and design of UV-A LEDs, this technology has promise for application in spacecraft and surface habitats.