Activated Carbon and Carbon Black Catalyzed Transformation of Aqueous Ozone into OH-Radicals

In an ozone-containing water a suspension of a few milligrams per liter of activated carbon (AQ or carbon black (CB) initiates a radical-type chain reaction that then proceeds in the aqueous phase and accelerates the transformation of O<SUB>3</SUB> into secondary radicals, such as hydroxyl radicals (°OH). This results in an Advanced Oxidation Process (AOP) that is similar to an O<SUB>3</SUB>-based AOP involving application of H<SUB>2</SUB>O<SUB>2</SUB> or UV-irradiation. We have studied these phenomena by observing the effect of suspensions of AC and CB on the rate of transformation of O<SUB>3</SUB> in lakewater and in well-characterized solutions. In addition, the stoichiometric yield factor of the AC-catalyzed conversion of O<SUB>3</SUB> into °OH has been shown to be comparable to that which is achieved by a slower process in the absence of AC. This comparison has been based on the measured depletion of an O<SUB>3</SUB>-resistant organic °OH probe that was added as a trace reference compound and that competed with a kinetic excess of solutes that controlled the lifetime of °OH. The AC-catalyzed transformation of O<SUB>3</SUB> into °OH for creating an O<SUB>3</SUB>-based AOP may be of practical interest to water utilities as an alternative to extended reaction times, to hydrogen peroxide addition, or to UV- catalyzed transformation of O<SUB>3</SUB>. We propose the name "Carbozone Process" for this new type of AOP.

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