Study On Degradation Characteristics And Mechanism Of Indomethacin In Water By Electron Beam Irradiation And UV/H₂O₂

Pharmaceutical and Personal Care Products?PPCPs?were emerging contaminants,and the accumulation of pharmaceutical compounds in the environment increased the risk to humans and ecosystems.Indomethacin?IDM?is a common nonsteroidal anti-inflammatory drug.A large number of IDM was discharged into the sewage treatment plant.In the traditional municipal wastewater treatment plant,the removal rate of IDM was less than 10%.In the natural environment,IDM is stable and difficult to be degraded.IDM could exist in natural environment for a long time,and even accumulate in organism through bioaccumulation.In order to solve the problem of indomethacin wastewater generated by production and life.In this paper,UV/H₂O₂ and electron beam irradiation technology was used to study the degradation of indomethacin,and the removal efficiency was compared.The degradation characteristics of indomethacin by three degradation techniques were studied.The technical conditions of degradation were optimized,and the impact of environmental factors on degradation was investigated.The attack sites of free radicals on IDM were studied and the degradation products were analyzed in the electron beam irradiation system.The degradation pathway of indomethacin was clarified,and the toxicity of intermediate products was evaluated.The results of the present research follow:?1?Natural light,UV and UV/H₂O₂were applied to degrade IDM.The degradation effects of IDM by various methods are as follows:UV/H₂O₂>UV>Natural light.?2?The degradation of indomethacin by UV/H₂O₂ follows pseudo-first-order kinetics.With the increase of IDM concentration,the consumption of·OH increased,the degradation efficiency decreased,and the apparent kinetic constant decreased.With the increase of the concentration of H₂O₂,the number of·OH increased and degradation efficiency was enhanced.Since too much H₂O₂ can quench·OH,it was difficult to improve the degradation efficiency.Adopting proper H₂O₂ concentration could improve the reaction rate while ensuring the technical economy.?3?In the UV/H₂O₂ degradation system,as the p H increased from 5 to 10,the apparent kinetic constant decreased from 0.159 to 0.122.Acidic conditions were conducive to the formation of·OH in the UV/H₂O₂ degradation system and promoted the degradation of indomethacin.Common anions in the environment,such as NO₃^-,NO,CO₃^2-,HCO₃^-,SO₃^2-,can inhibit the degradation of IDM by competing for·OH.The inhibitory effects of these anions on IDM degradation were ranked as follows:NO₂^->acid would inhibit the degradation of indomethacin.?4?Electron beam irradiation technology can efficiently and rapidly degrade IDM,and completely removed 300?M IDM in tens of seconds.The degradation process of IDM accorded with pseudo-first-order kinetics.As the concentration of indomethacin increases,the dose constant decreases,which could be expressed in the form of a power function,k=376.61C₀^0.927.The higher the initial concentration of IDM was,the higher the radiation chemical yield?G-value?,that is,the more IDM that can be degraded per unit of energy.Adjusting the appropriate concentration of IDM was necessary to achieve the desired removal efficiency and a high radiation chemical yield at the same time.The economic degradation scheme was obtained by optimization.?5?According to the quenching experiment,the dose constant ratios of oxidative radicals?·OH?and reductive radicals?e_a^-_q and·H?could be calculated as k_·OH:k^-_{ea q and·H}=4.79:1.The three active species?·OH,eand·H?produced by irradiation could attack indomethacin and lead to dechlorination.At 10 k Gy,the dechlorination rate was91.7%.When the solution was aerated with oxygen,the degradation efficiency and dechlorination rate of IDM can be improved.With the increase of p H value from 5 to10,the dose constant decreased from 1.979 k Gy^-1 to 1.587 k Gy^-1.Under acid condition,it was more favorable for the formation of·OH and the degradation of IDM.As the concentration of H2O2 increased from 0 m M to 10 m M,the dose constant increased from 1.883 k Gy^-1 to 2.582 k Gy^-1.If the concentration of H2O2 continued to increase,which could quench·OH in the system,the dose constant would decrease.Several common anions(NO₃^-,NO₂^-,CO₃^2-,HCO₃^-,SO₃^2-)and humic acids can inhibit the degradation efficiency by competing for active species.The inhibition rate of·OH,e_a^-_qand·H by typical anions and organic matter in different medium were calculated,which showed that more anions and organic matter,which can act as inhibitors in the wastewater,have a stronger inhibitory effect on the degradation of IDM.In various water medium,the degradation efficiency was ranked as:pure water>surface water>wastewater.?6?Compared with the electron beam irradiation and UV/H₂O₂ degradation technology,it took more than 20 minutes for UV/H₂O₂ to degrade 50?M IDM,while it only took tens of seconds for a higher concentration of 300?M IDM.Electron beam irradiation had obvious advantages in the treatment of high concentration and high load IDM wastewater.Due to the existence of various active substances in the degradation system of electron beam irradiation,compared with the UV/H₂O₂ degradation technology,there were more degradation pathways for IDM by electron beam irradiation,which had a stronger ability to resist stress changes to the influence of ions or organic matter in wastewater.?7?14 kinds of intermediate products were detected by high-resolution mass spectrometer during the electron beam irradiation process.The molecular structure of indomethacin was optimized by Gaussian 08.The reactive sites of each active substance were calculated by condensed Fukui function,including the reactive sites corresponding to nucleophilic attack,electrophilic attack,and free radical attack.The degradation pathway of IDM by the attack of various active species was clarified.The attack of·OH mainly resulted in the cleavage of amide bond,indole ring opening,demethoxylation and·OH addition.Dechlorination and the reduction of the carbonyl group occurred on IDM molecular through the reduction of e_a^-_q and·H.The intermediates could continue to be degraded to small molecule acid,such as formic acid,acetic acid,oxalic acid.?8?ECOSAR program calculations showed that the degradation intermediate P6is more toxic than the parent compound.However,it could continue to be degraded into P7.When IDM was completely removed,P6 was also completely degraded.Therefore,highly toxic IDM transformed into less toxic products during the irradiation process,which reduced the risk to the ecological environment.