Degradation of selected pharmaceuticals in aqueous solution with UV and UV/H 2O 2

Abstract

The degradation of four pharmaceutical compounds (PhACs), ibuprofen (IBU), diphenhydramine (DP), phenazone (PZ), and phenytoin (PHT) was investigated via ultraviolet (UV) photolysis and UV/H 2O 2 process with a low-pressure (LP) UV lamp. For each PhAC tested, direct photolysis quantum yields at 254 nm were found to be ranging from 6.32 × 10 −2 to 2.79 × 10 −1 mol E −1 at pH 7. The second-order rate constants of the reaction between the PhACs and OH were determined to be from 4.86 × 10 9 to 6.67 × 10 9 M −1 s −1 by using a competition kinetic model which utilized para-chlorobenzoic acid ( pCBA) as a reference compound. The overall effect of OH radical scavenging from humic acid (HA) and anions HCO 3 −, NO 3 − was measured utilizing R OH,UV method through examining the aqueous photodegradation of pCBA as a probe compound. Moreover, these fundamental direct and indirect photolysis parameters were applied in the model prediction for oxidation rate constants of the PhACs in UV/H 2O 2 process. It was found that the predicted oxidation rate constants approximated the observed ones. The results indicated that the new R OH,UV probe compound method was applicable for measuring background OH radical scavenging effects in water treatment process of UV/H 2O 2. Furthermore, by GC–MS analysis, most of the intermediates created during the photodegradation of the selected PhACs in UV/H 2O 2 process were identified. For the photodegradation of PZ, a competition mechanism existed between the direct UV photolysis and the oxidation of OH. An appropriate dosage of H 2O 2 could hinder the occurrence of the direct photolysis.