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This work describes the microbiological assessment and materials compatibility of a silver-based biocide as an alternative to iodine for the Crew Exploration Vehicle (CEV) and future spacecraft potable water systems. In addition to physical and operational anti-microbial counter-measures, the prevention of microbial growth, biofilm formation, and microbiologically induced corrosion in water distribution and storage systems requires maintenance of a biologically-effective, residual biocide concentration in solution and on the wetted surfaces of the system. Because of the potential for biocide depletion in water distribution systems and the development of acquired biocide resistance within microbial populations, even sterile water with residual biocide may, over time, support the growth and/or proliferation of bacteria that pose a risk to crew health and environmental systems.

Our long term objective is to utilize the photocatalytic property of titanium dioxide (TiO2) to convert volatile organic compounds (VOC) in contaminated air to carbon dioxide as a measure of total organic carbon (TOC) for risk assessment in space crafts. Photocatalytically active TiO2 surfaces prepared using Degussa P25 and sol-gel methods were evaluated for this purpose. Photocatalytic oxidation (PCO) of representative air contaminants (e.g. ethanol, toluene, dichloromethane, and acetaldehyde) by Degussa P25 immobilized on aluminum substrate revealed several shortcomings that are not suitable for our intended application. A series of experiments were conducted to optimize parameters during TiO2 sol preparation and thin film deposition.

This project sought to develop a photocatalytic oxidation (PCO) based total organic carbon (TOC) analyzer for real time monitoring of air quality in spacecraft. Specific requirements for this application were to convert volatile organic contaminants (VOC) into CO2 stoichiometrically in a single pass through a small reactor with low power requirement. One of the greatest challenges of this TiO2-mediated PCO was the incomplete oxidation of some recalcitrant VOCs leading to less reactive intermediates that deactivate the catalyst over time. Dichloromethane (DCM) is one of these VOCs. The effect of some design factors (e.g. TiO2 catalyst surface area to volume ratio and UV photon flux field) as well as operating conditions of an annular reactor (e.g. VOC residence time and relative humidity) on the efficiency in converting DCM to CO2 were investigated.