Degradation of selected pharmaceuticals in aqueous solution with UV and UV/H2O2

The degradation of four pharmaceutical compounds (PhACs), ibuprofen (IBU), diphenhydramine (DP), phenazone (PZ), and phenytoin (PHT) was investigated via ultraviolet (UV) photolysis and UV/H2O2 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 × 109 to 6.67 × 109 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 HCO3−, NO3− was measured utilizing ROH,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/H2O2 process. It was found that the predicted oxidation rate constants approximated the observed ones. The results indicated that the new ROH,UV probe compound method was applicable for measuring background OH radical scavenging effects in water treatment process of UV/H2O2. Furthermore, by GC–MS analysis, most of the intermediates created during the photodegradation of the selected PhACs in UV/H2O2 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 H2O2 could hinder the occurrence of the direct photolysis.