The photolysis of the antibiotic sulphamethoxazole (SMX) using a low pressure ultraviolet (UV) lamp with emission of monochromatic wavelength at 254 nm was evaluated in Milli-Q water and the effluent from a real sewage treatment plant (STP). The effects of various parameters including initial SMX concentration, solution pH, a variety of inorganic anions (Cl(-1), SO4(2-), NO3- and HCO3-) and humic acid (HA) have been assessed. The results showed that 10 mg L(-1) of SMX was removed within 30 min of irradiation in Milli-Q water. The removal of SMX fitted the pseudo-first-order kinetic model with the rate constants in the range of 0.170 to 0.932 min(-1) for initial SMX concentrations of 1.0 to 10 mg L(-1). Solution pHs of 2.0-5.5 were more favourable for SMX degradation, compared with caustic conditions. On the other hand, slight improvements in SMX degradation in water matrixes with Cl-, SO4(2-) and NO3- anions at 1.0 mM concentration and HA (when used at 5 mg L(-1)) were observed. However, HCO3-(used at 1.0 mM) and HA (when used at concentrations of 20, 50 and 100 mg L(-1)) slowed down the degradation rate. The complete degradation of SMX was almost achieved in STP effluent spiked with 10 mg L(-1) of SMX after 60 min of irradiation, and the rate constants showed that the turbidity in STP effluent had no significant adverse effect on SMX removal. Total organic carbon was hardly changed even after 8 h of irradiation, showing negligible mineralization of its intermediates under UV254 irradiation.
The efficiency of UV-and VUV-based processes (UV, VUV, UV/H 2 O 2 , and VUV/H 2 O 2 ) 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/H 2 O 2 > VUV > UV/H 2 O 2 > 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/H 2 O 2 and VUV/H 2 O 2 , 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.
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