Degradation Of Typical PPCPs By UV-LED/NaClO Advanced Oxidation Process

As a typical pharmaceuticals and personal care products?PPCPs?pollutant,acetaminophen?AAP?has potential harm to human body and aquatic organisms.Traditional water treatment process was poorly to remove AAP,and more toxic pollutants will be generated in the removal process.Therefore,the combined process of UV-LED and NaClO was applied to degraded AAP.The degradation of AAP by UV-LED/NaClO was systematically explored and the study was divided into four sections,including reaction kinetics,water quality factors,degradation mechanism and toxicity evaluation.The results are summarized as follows:The UV-LED/NaClO process significantly increased the degradation of AAP compared with UV-LED radiation and NaClO oxidation alone.Meanwhile,the ultraviolet light source with a wavelength of 278 nm had a better efficient to remove AAP than 308 nm and 365 nm,and had a lower cost(Cost/O_total).The degradation of AAP significantly increased with increasing the concentration of NaClO,whereas overdosing inhibited the degradation of AAP during the UV-LED/NaClO process.A comparative study of four different UV-LED-based advanced oxidation processes?UV-LED/NaClO,UV-LED/PS,UV-LED/H₂O₂,and UV-LED/NH₂Cl?showed that UV-LED/NaClO was the most efficient process for AAP degradation.In the UV-LED/NaClO system,free radicals quenching experiment showed that the AAP degradation was involved in the participation the hydroxyl radical?HO×?and reactive chlorine radicals?RCS?.The second-rate constants of HO×with AAP was calculated to be 8.87?10⁹M^-1s^-1and the relative contribution rates of UV-LED radiation,HO×,NaClO,and RCS to AAP degradation were 0.66%,4.23%,33.78%and 61.33%.The degradation rate constant(k_obs)first increased and then decreased with the p H increased from 3.0 to 11.0,and neutral condition was conducive to AAP degradation.The presence of HCO₃^-and NO₃^-could promoted the AAP degradation.However,AAP degradation was significantly inhibited with increasing concentration of HA.The AAP degradation in tap water and real water was inhibited compared with that in ultrapure water.The intermediates of AAP degradation in UV-LED/NaClO process were identified by LC/MS and GC/MS,and the possible degradation pathways were proposed.The major intermediates were 1,4-benzoquinone,hydroquinone,1,2,4-Trihydroxybenzene and 2-hydroxy-4-?N-acetyl?-aminophenol,the proposed mechanism were mainly the substitution,addition and oxidation reaction of HO×,NaClO and RCS.For the acute toxicity test,the inhibition rate of the AAP solution increased from 25%to 32%and finally decreased to 18%with the increase of the reaction time.The concentration of 1,4-benzoquinone and hydroquinone increased first and then decreased,which was similar to the change of acute toxicity.ECOSAR software evaluated the acute and chronic toxicity of AAP and intermediates to aquatic organisms.The results showed that the ecotoxicity of intermediates was higher than AAP,but the ecotoxicity of the final products was significantly lower than AAP.