The Efficiency And Mechanism Of Photocatalytic Oxidation Of Acetanilide Drugs Based On UV-LED

In response to the frequent detection of non-steroidal anti-inflammatory drugs（NSAIDs）in surface water and water treatment processes,ultraviolet-light-emitting diodes（UV-LED）with a wavelength of 365 nm were applied as light source in this study.Two typical NSAIDs,including phenacetin（PNT）and acetaminophen（ACT）,were employed as the target contaminants which were degraded by three oxidants in this study,including hydrogen peroxide（H₂O₂）,free active chlorine（FAC）,and persulfate（PS）.The effects of oxidant dosage,light intensity,and p H on the degradation of NSAIDs by UV₃₆₅-LED/H₂O₂,UV₃₆₅-LED/FAC,and UV₃₆₅-LED/PS were investigated.In UV₃₆₅-LED/H₂O₂ system,the removal and k_obs of ACT degradation in 60 min reached the highest values of 29.2%and 5.9×10^-3 min^-1 at p H 3.0,respectively.The removal and k_obs of PNT in60 min reached highest values of 31.2%and 6.0×10^-3 min^-1 at p H 5.0,respectively.In UV₃₆₅-LED/FAC system,the removal efficiency of pollutants was the highest at p H 8.5,and the removal of PNT and ACT are 100%and 100%in 15 min,corresponding to k_obs of 2.3×10^-1and 4.7×10^-1 min^-1,respectively.In UV₃₆₅-LED/PS system,the best removal efficiency of pollutants was observed at p H 8.5,and PNT and ACT were completely degraded within 60min,corresponding to the k_obs of 1.8×10^-1and 1.2×10^-1 min^-1,respectively.Qualitative and quantitative identification of reactive oxygen species（ROS）in each system were conducted by electronic spin-resonance（ESR）spectroscopy and alcohol suppression experiments.The results showed that the main type of ROS is hydroxyl radical（·OH）in UV₃₆₅-LED/H₂O₂ system.The dominated ROS species in UV₃₆₅-LED/FAC system are·OH,ozone（O₃）and reactive chlorine radical（RCS）.Additionally,the types of ROS in UV₃₆₅-LED/PS system are mainly·OH,sulfate radical（SO₄·^-）,singlet oxygen（¹O₂）and superoxide radical（O₂^-·）.In UV₃₆₅-LED/FAC system,the average contribution of RCS was the highest of 57.4%for PNT degradation.For ACT removal,FAC accounted for the highest contribution with contribution of 51.3%.However,in UV₃₆₅-LED/PS system,SO₄·^-accounted for the highest average contribution for PNT（52.9%）and ACT（3.0%）decomposition.The mineralization of three systems were further tested in study,and the actual mineralization rate in three systems was lower than the pollutant removal.The concentration and toxicity of disinfection by-products of UV₃₆₅-LED/FAC system at p H 8.5 were significantly reduced compared to the system of FAC alone.At p H 5.5 and 7.0,after UV₃₆₅-LED/PS system pre-oxidation,the concentration and toxicity of disinfection by-products also decreased significantly.Through economic analysis,the range of EE/O values in the UV₃₆₅-LED/H₂O₂,UV₃₆₅-LED/FAC,and UV₃₆₅-LED/PS systems were in ranges of 1.80～2.97,0.046～0.086,and 0.089～0.137 k Wh/m³/order,respectively,indicating that UV₃₆₅-LED activated oxidant process could be feasible in actual water treatment projects.