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 te mperature (10, 20, 30 and 40 degreesC), pH (2, 5, 7 and 9) and ozone partia l pressure (0.10-0.38 kPa) on the conversion of p-hydroxybenzoic acid were established. Experimental results indicated that the kinetics for both oxid ation processes fit pseudo-first-order kinetics well. In the combined proce ss, the overall kinetic rate constant was split into two components: direct oxidation by UV radiation (photolysis) and oxidation by free radicals (mai nly OH.) generated in the system. The importance of these two reaction path s 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 kn own operating variables. (C) 2001 Society of Chemical Industry.