Treatment Of Antibiotic Wastewater By Dielectric Barrier Discharge Coupled With Persulfate

Tetracycline hydrochloride（TCH）,as a typical broad-spectrum antibiotic,is widely used in clinical medicine and aquaculture industry.Because the traditional sewage treatment process is difficult to completely degrade tetracycline hydrochloride in wastewater,in recent years,a certain concentration of tetracycline hydrochloride and its by-products have been continuously detected in natural water bodies,which are toxic to humans and other organisms.Therefore,it is urgent to find an effective method to deeply treat it.Dielectric barrier discharge plasma technology is a new advanced oxidation technology,which can rapidly degrade tetracycline hydrochloride molecules by using active radicals and high-energy particles generated by discharge.However,its large-scale application is hindered by high energy consumption and low energy utilization efficiency.Therefore,in this study,persulfate（PS）is coupled with dielectric barrier discharge plasma technology,and persulfate is activated by ultraviolet light,ultrasound and high-energy particles generated by discharge,so that the whole reaction system generates more sulfate radical(SO₄^·-)and hydroxyl radical（·OH）to improve the removal rate and mineralization rate of tetracycline hydrochloride,and reduce energy consumption.The specific research contents are as follows:A new coaxial cylindrical reaction device was designed and manufactured.The reaction device improved the gas-liquid mass transfer efficiency by producing a uniform water falling film,increased the contact area between active oxidation substances and TCH molecules,and repeatedly treated wastewater through the solution circulation system,greatly improving the removal rate of TCH and the degree of mineralization.The simulated wastewater of TCH was treated by DBD plasma technology.The results show that the kinetic process of the reaction conforms to the second-order reaction kinetic model;In a certain range,the increase of input power is conducive to the improvement of the removal rate of TCH,but too high input power will lead to a decline in the degradation effect;The change of circulating flow rate of solution will also cause the fluctuation of removal rate.With the increase of circulating flow rate,the removal rate will first increase and then decrease.The circulating flow rate at the highest removal rate is 90m L/min;When the initial concentration is within the range of 100mg/L～150mg/L,the removal rate is high.When the initial concentration is lower than 100mg/L or higher than 150mg/L,the removal rate will decrease;With the increase of initial conductivity,the removal rate of TCH first increased and then decreased,and the conductivity of the solution continued to increase with the reaction;Alkaline and neutral environments were more conducive to the removal of TCH,and the p H of solution continued to decline during the treatment process,and finally stabilized at about 1.60;A large number of intermediate by-products were generated in the treatment process,and only a few TCH were completely mineralized;The results of liquid chromatography-mass spectrometry（LC-MS）showed that during the treatment process,TCH intermediates were mainly formed through three ways:the defunctioning reaction,the ring opening reaction and the hydroxylation reaction through the addition or substitution of·OH.Seven major degradation intermediates of TCH were identified,according to which an approximate pathway for the degradation of TCH was proposed.The simulated wastewater of TCH was treated by DBD plasma coupled PS technology.The results showed that the kinetic process of TCH degradation in DBD/PS system could be described by the second-order reaction kinetic model;The increase of input power is beneficial to the improvement of TCH removal rate.Under the conditions of PS:TCH=20:1 and input power of 170W,the degradation rate reaches 86.69%;When PS:TCH increases from 0:1 to 80:1,the removal rate of TCH increases significantly,especially when PS:TCH=80:1,the removal rate reaches the maximum of 87.90%,indicating that the addition of PS is conducive to the degradation of TCH,while the initial conductivity of the solution has little effect on the degradation of TCH;DBD/PS system can effectively degrade TCH in a wide p H range,among which the removal efficiency of TCH is the highest in acidic environment,followed by neutral environment,and the lowest in alkaline environment;Adding Fe²⁺and PS to the simulated wastewater of TCH can promote the degradation of TCH molecules by plasma,because plasma Fenton reaction and PS activation will produce more·OH and SO₄^·-,so it can be seen that DBD,Fe²⁺and PS have obvious synergistic effects;The addition of Cl^-inhibited the degradation of TCH in DBD/PS system.After adding PS,most TCH and its degradation intermediates in the solution are completely mineralized into CO₂,H₂O and other small molecular inorganic substances;The different degradation performance degradation caused by Et OH and TBA in DBD and DBD/PS systems showed that·OH and SO₄^·-played an important role in the degradation of TCH;When 0.5m M NO₃^-was added to DBD and DBD/PS systems,the degradation rate of TCH in the solution decreased by 7.16%and 4.68%,respectively,indicating that electrons played an important role in the generation of·OH and the activation of PS;Both O₃and H₂O₂are consumed in the treatment process,so they have oxidative degradation effect on TCH;LC-MS results show that aromatic rings,double bonds and amino groups in the molecular structure of TCH are vulnerable to attack by strong oxidizing free radicals.Intermediates are mainly formed through three ways:addition,hydrogen atom separation and electron transfer,which lead to ring opening and bond breaking reactions of organic compounds.In addition,five major degradation intermediates of TCH have been identified,and a possible degradation path of TCH molecule has been proposed accordingly.