Advanced oxidation processes for the degradation of p-hydroxybenzoic acid 1:: Photo-assisted ozonation

The oxidation of p-hydroxybenzoic acid in aqueous solution by UV radiation and by photoassisted ozonation (UV+O-3) has been studied. The effects of temperature (10, 20, 30 and 40 degreesC), pH (2, 5, 7 and 9) and ozone partial pressure (0.10-0.38 kPa) on the conversion of p-hydroxybenzoic acid were established. Experimental results indicated that the kinetics for both oxidation processes fit pseudo-first-order kinetics well. In the combined process, the overall kinetic rate constant was split into two components: direct oxidation by UV radiation (photolysis) and oxidation by free radicals (mainly OH.) generated in the system. The importance of these two reaction paths for each specific value of ozone partial pressure, temperature and pH was quantified. Lastly, a general expression is proposed for the reaction rate which takes into account the two reaction pathways and is a function of known operating variables. (C) 2001 Society of Chemical Industry.