Two-phase ozonation of hazardous organics in single and multicomponent systems

The destruction of pentachlorophenol (PCP), oxalic acid, chlorendic acid, and a mixture of pentachlorophenol, 1,3-dichlorobenzene (DCB), and trichloroethylene (TCE) were studied using a two-phase ozonation system. A two-phase ozonation system consists of water containing the pollutant and a second solvent phase which houses the ozone. The solvent phase is an inert fluorinated hydrocarbon (FC40) that is nonpolar and reusable. The solvent phase is desirable because it has a high ozone stability (k = 0.0033 min^-1) and an ozone solubility of 120 mg/L at 25°C, 10 times that of water. In addition to an enhanced oxidation rate of PCP, less ozone was utilized. At high pH (10.3), a first-order rate constant of 200 min^-1 in the two-phase system was found for PCP degradation compared to k(app) = 0.154 min^-1 in a single aqueous-phase system. Within 15 s, the concentration of PCP (100 mg/L initially) was degraded more than 90%, and 100% dechlorination was obtained with longer reaction times. This system also demonstrated the ability to selectively oxidize PCP while in the presence of free radical scavengers existing in the water phase. PCP was also successfully oxidized using actual wastewater which contained alkalinity, hardness, many inorganics, and trace hazardous organics. Oxalic acid, an intermediate formed during the degradation of PCP, was also degraded by two-phase ozonation. Preliminary work with chlorendic acid showed that two-phase ozonation was faster than single aqueous-phase ozonation at dechlorinating the compound. TCE and DCB degraded slightly faster when PCP was added to the mixture, possibly due to the production of other radicals during the oxidation of PCP.