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Small, highly polar organics such as urea, alcohols, acetone, and glycols are not easily removed by the International Space Station's Water Recovery System. The current design utilizes the Volatile Removal Assembly (VRA) which operates at 125°C to catalytically oxidize these contaminants. Since decomposition of these organics under milder conditions would be beneficial, several ambient temperature biocatalytic and catalytic processes were evaluated in our laboratory. Enzymatic oxidation and ambient temperature heterogeneous catalytic oxidation of these contaminants were explored. Oxidation of alcohols proceeded rapidly using alcohol oxidase; however, effective enzymes to degrade other contaminants except urea were not found. Importantly, both alcohols and glycols were efficiently oxidized at ambient temperature using a highly active, bimetallic noble metal catalyst.

The destruction of organic contaminants in waste water for closed systems, such as that of the International Space Station, is crucial due to the need for recycling the waste water. A cocurrent upflow bubble column using oxygen as the gas phase oxidant and packed with catalyst particles consisting of a noble metal on an alumina substrate is being developed for this process. This paper addresses the development of a plug-flow model that will predict the performance of this three phase reactor system in destroying a multicomponent mixture of organic contaminants in water. Mass balances on a series of contaminants and oxygen in both the liquid and gas phases are used to develop this model. These mass balances incorporate the gas-to-liquid and liquid-to-particle mass transfer coefficients, the catalyst effectiveness factor, and intrinsic reaction rate.