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) LTV lamp. For each PhAC tested, direct photolysis quantum yields at 254 nm were found to be ranging from 6.32 x 10(-2) to 2.79 x 10(-1) mol E-1 at pH 7. The second-order rate constants of the reaction between the PhACs and (OH)-O-center dot were determined to be from 4.86 x 10(9) to 6.67 x 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)-O-center dot radical scavenging from humic acid (HA) and anions HCO3-, NO3- was measured utilizing R-OH,R-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 R-OH,R-UV probe compound method was applicable for measuring background (OH)-O-center dot 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)-O-center dot. An appropriate dosage of H2O2 could hinder the occurrence of the direct photolysis. (C) 2009 Elsevier Ltd. All rights reserved.