Photodegradation of Sulfamethoxazole Applying UV- and VUV-Based Processes

Abstract

The efficiency of UV- and VUV-based processes (UV, VUV, UV/H2O2, and VUV/H2O2) for removal of sulfamethoxazole (SMX) in Milli-Q water and sewage treatment plant (STP) effluent was investigated at 20°C. The investigated factors included initial pH, variety of inorganic anions (NO 3 − and HCO 3 − ), and humic acid (HA). The results showed that the degradation of SMX in Milli-Q water at both two pH (5.5 and 7.0) followed the order of VUV/H2O2 > VUV > UV/H2O2 > UV. All the experimental data well fitted the pseudo-first order kinetic model and the rate constant (k) and half-life time (t 1/2) were determined accordingly. Indirect oxidation of SMX by generated •OH was the main degradation mechanism in UV/H2O2 and VUV/H2O2, while direct photolysis predominated in UV processes. The quenching tests showed that some other reactive species along with •OH radicals were responsible to the SMX degradation under VUV process. The addition of 20 mg L−1 HA significantly inhibited SMX degradation, whereas, the inhibitive effects of NO 3 − and HCO 3 − (0.1 mol L−1) were observed as well in all processes except in UV irradiation for NO 3 − . The removal rate decreased 1.7–3.6 times when applying these processes to STP effluent due to the complex constituents, suggesting that from the application point of view the constituents of these complexes in real STP effluent should be considered carefully prior to the use of UV-based processes for SMX degradation.