An improved water-sterilizing aqueous-phase catalytic oxidation system (APCOS) is based partly on the electrochemical generation of hydrogen peroxide (H2O2). This H2O2-boosted system offers significant improvements over prior dissolved-oxygen water-sterilizing systems in the way in which it increases oxidation capabilities, supplies H2O2 when needed, reduces the total organic carbon (TOC) content of treated water to a low level, consumes less energy than prior systems do, reduces the risk of contamination, and costs less to operate. This system was developed as a variant of part of an improved waste-management subsystem of the life-support system of a spacecraft. Going beyond its original intended purpose, it offers the advantage of being able to produce H2O2 on demand for surface sterilization and/or decontamination: this is a major advantage inasmuch as the benign byproducts of this H2O2 system, unlike those of systems that utilize other chemical sterilants, place no additional burden of containment control on other spacecraft air- or water-reclamation systems.

This system produces H2O2 in an electrochemical/electrodialytic process that consumes only electrical energy and oxygen; that is, unlike some other systems, this system consumes no expensive chemicals. The system includes an H2O2 generator, an H2O2-pervaporation membrane, and an APCOS reactor.

Tests have verified that H2O2 can be easily transferred and delivered from a stream identical to that in the central compartment of an electrodialytic cell to a required process stream. Test results have also shown that at stoichiometric concentrations, H2O2 promotes the increased destruction of urea and of NH3 (the chief byproduct of urea) in wastewater. Heretofore, NH3 has been considered one of the more intractable contaminants for oxidation purposes. Data indicate that oxidation occurs at high rates at low temperatures — an important advantage in that the consumption of energy is reduced and safety increased, relative to prior oxygen-boosted systems that must operate at higher temperatures. Moreover, the ability of this system to oxygenate highly contaminated wastewater was proved by the nearly complete oxidation of 500 mg/L of acetic acid (TOC = 200 mg/L). Considered together, these data are a convincing argument for using electrochemically produced H2O2 to boost APCOS oxidation rates in highly contaminated wastewater.

This work was done by James R. Akse, John O. Thompson, and Leonard J. Schussel of Umpqua Research Co. for Johnson Space Center. For further information, contact the Johnson Commercial Technology Office at (281) 483-3809.


NASA Tech Briefs Magazine

This article first appeared in the February, 2004 issue of NASA Tech Briefs Magazine.

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