The markets for ozone in industrial water and wastewater treatment are quite small. Industrial applications for ozone could grow. The use of ozone for treating photoprocessing solutions is a novel application that has been limited, but might grow. In this process, silver is recovered electrolytically; then the spent bleach baths of iron ferrocyanide complexes are ozonated. Iron cyanide complexes are stable to ozonation so that the ferrous iron is merely oxidized to ferric, which is its original form. Thus, the bleach is "regenerated" and is ready for recycling and reuse by the photoprocessor.
Ideally, 20.2 pounds of the ferrocyanide can be converted to 11.7 pounds of ferricyanide by one pound of ozone. Indeed, ozone oxidation efficiency is nearly 100 percent for ferrocyanide concentrations above 1.0 g/1. A typical ozone system consists of 100 g/hr at a concentration of 1.0 percent to 1.5 percent in air fed to the bottom of bleach collection tanks through ceramic spargers (pore size of approximately 100 ~t). The system contains air compression and drying equipment, automatic control features, and a flat-plate, air-cooled ozone generator. Regeneration of bleach wastes totaling about 10,000 gallons a year, and recovery of other chemicals can also be cost effective.
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