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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.

With the installation of the Water Recovery System (WRS) during mission STS-126 in 2008, the International Space Station (ISS) added the capability to recover clean water for reuse from crewmember urine and atmospheric humidity condensate, including EVA (Extravehicular Activity) wastes. The ability to collect, store and process these waste streams is required to increase potable water recovery and support the ISS crew augmentation planned for 2009. During ground testing of the Urine Processing Assembly (UPA), one of two primary component subsystems that comprise the WRS, significant fouling was repeatedly observed in stored urine pretreated with 0.56% of chromium trioxide and sulfuric acid. During initial observation, presumptive microbiological growth clogged and damaged flight-rated hardware under test as part of a risk-mitigation Flight Experiment (FE).

A multitude of personal cleaning products, each of which typically contains multiple surfactants, are available for terrestrial use. Selection of surfactant(s) for use in extended space missions should consider, in addition to human comfort and cleansing power, potential impacts on biological processing systems under consideration for such missions. This paper reviews the surfactants present in commercial formulations, their proper nomenclature, and relevant properties such as foaming, biodegradability of organic fractions (both with respect to rate and pathway), presence of inorganic components (e.g., sulphate or counter ions such as sodium), and analytical methods for monitoring their concentrations in waste stream. The background information and results from preliminary testing are used to draw conclusions about the proper approach for selecting surfactants for use in space missions containing biological waste treatment systems.