Electrochemical systems that are especially well suited for the small-scale generation of ozone and ozonated water for local use have been invented. These systems can operate with very little maintenance, and the only inputs needed during operation are electric power and water. These systems are closely related to the ones described in "Electrochemical Systems Generate Ozone and Ozonated Water" (MSC-23046), NASA Tech Briefs, Vol. 26, No. 3 (March 2002), page 68. Ozonated water produced by these systems can be used in diverse industrial applications: A few examples include sterilization in the brewing industry, general disinfection, and treatment of sewage and recycled water.
The basic principle of operation admits of several alternative system configurations, of which one is depicted schematically in the figure. The heart of the system is a stack of electrolytic cells, each containing a proton-exchange membrane (which serves as a solid electrolyte) sandwiched between a catalytic anode and a catalytic cathode. Preferably, the proton-exchange membrane is made of a perfluorinated sulfonic acid polymer. During electrolysis, a mixture of O2 and O3 gases is generated at the anode and H2 is generated at the cathode. Some of the O3 generated at the anode becomes dissolved in the water. The proportion of O3 in the O2/O3 mixture can be maximized by the selection of suitable electrode materials and the use of a high overpotential. Although the proton-exchange membrane conducts protons, it does not conduct electrons. It is also impermeable by gases; consequently, it maintains separation between the O2/O3 mixture evolved at the anode and the H2 evolved at the cathode.
Water circulates upward through the anode and cathode compartments of the stack of electrolytic cells. Water from the bottom of an anode and a cathode reservoir is gravity-fed to the bottom inlet of the anode and cathode compartment, respectively. From the tops of the anode compartments, the mixture of water and O2 and O3 gases and water containing dissolved ozone can flow freely upward, through a standpipe that ends in the anode reservoir, and from the tops of the cathode compartments, the mixture of water and H2 gas can flow freely upward, through standpipe that ends in the cathode reservoir. The reservoirs double as liquid/gas separators: O2 and O3 diffuse out of the water in the anode reservoir, are collected at the top of the reservoir, and are either vented or sent to an ozone-consuming process. Similarly, H2 diffuses out of the water in the cathode reservoir, is collected at the top of that reservoir, and can be flared, vented, or sent to an H2-consuming process.