Assessment of Silver Based Disinfection Technology for CEV and Future US Spacecraft

Silver biocide offers a potential advantage over iodine, the current state-of-the-art in US spacecraft disinfection technology, in that silver can be safely consumed by the crew. As such, silver may reduce the overall complexity and mass of future spacecraft potable water systems, particularly those used to support long duration missions. A primary technology gap identified for the use of silver biocide is one of material compatibility. Wetted materials of construction are required to be selected such that silver ion concentrations can be maintained at biocidally effective levels. Preliminary data on silver biocide depletion rates in heritage spacecraft potable water system wetted materials of construction has been gathered as part of a multi-phase test project aimed at the characterization of silver based biocide technology through: development of preferred materials lists, investigation of silver biocide forms and delivery methods, down-selection of silver biocide technologies, and integrated testing. Preliminary test data has shown a 10 to 20% loss in silver ion concentration per day for acid passivated Nitronic 40 tubing tested at surface area to volume (S/V) ratios approximating 4.59 cm^-1. The Nitronic tubes were tested both with and without biocide pretreatment. Silver biocide depletion was also observed at approximately 0.1% per day for the first 35 days of exposure to acid passivated Inconel 718 coupons tested at low S/V ratios, ∼ 0.14 cm^-1. Surface analysis by scanning electron microscopy (SEM) suggested deposition of silver metal on both test materials. SEM analysis also provided evidence of potential variability in the passivation process when using materials tested in a tube format. These preliminary results are presented and discussed herein, along with the current project status.