Study On Activating Persulfate By Water Falling Film DBD Plasma For Degradation Of Antibiotics

In recent years,antibiotic pollutants are frequently detected in various water environments.Because of bacteria and other microorganisms are sensitive to antibiotics,the commonly used biological treatment methods in wastewater treatment plants have poor treatment effect on antibiotic pollutants.A variety of active substances（such as hydroxyl radical（·OH））produced by plasma technology can react with antibiotics in water to degrade pollutants.Plasma has the advantages of convenient operation and quick reaction,but it needs high energy consumption.Therefore,improving the energy efficiency of pollutant degradation in discharge plasma is a research hotspot of this technology.It has been found that the degradation efficiency of pollutants can be improved significantly after persulfate in the advanced oxidation technology is activated as a strong oxidation radical of sulfate（SO₄·^-）.The redox potential of SO₄·^-is slightly higher than that of·OH,but the lifetime of SO₄·^-is much longer than that of·OH,so it is easier to oxidize pollutant molecules in water.Because of the physical and chemical effects of persulfate activation can be produced due to the formation of discharge plasma.In this study,Peroxymonosulfate（PMS）and peroxydisulfate（PS）were introduced into a water falling film dielectric barrier discharge（DBD）plasma system to improve the degradation effect of pollutants and reduce energy consumption by using SO₄·^-and·OH.Main research content and results:（1）The water falling film DBD reactor was designed.The effects of different experimental parameters on the degradation of sulfamethoxazole（SMX）in water falling film DBD plasma system were investigated,and the generation of long-lived active substances in the discharge process was studied.The results show that the degradation rate of SMX increases with the increase of pulse discharge voltage;The air flow rate and liquid circulation flow rate have little effect on the degradation of SMX in water;The degradation of SMX was favorable under alkaline conditions;The initial concentration of SMX increased,which would reduce the degradation effect of SMX;The degradation effect of solution conductivity on SMX was not significant.The ozone and hydrogen peroxide generated by discharge can produce more·OH,and the content of·OH increases with the increase of p H value.（2）The effects of different experimental parameters on the degradation of SMX in PMS and PS system and the effects of PMS/PS on the long-lived active substances produced by discharge were studied.When the discharge voltage was 24 k V and the discharge time was 30min,the removal rate of SMX was only 22.8%,while the degradation rates of SMX were 77.1%and 85.1%at 26 k V and 28 k V,respectively.After adding PMS/PS,the degradation rate of PS system and PMS system is 30.1%and 34.9%respectively at 24 k V;At 26 k V,the degradation rate of PS system and PMS system is 80.3%and 88.9%,respectively;At 28 k V,the degradation rate of PS system and PMS system is 95.4%and 98.9%,respectively;The results show that the degradation effect and energy utilization of SMX are PMS system>PS system>single DBD system at the same voltage;When the discharge power is fixed,the degradation effect of SMX is almost unchanged,whether the frequency is increased to keep the voltage constant or the voltage is increased;With the increase of PMS/PS concentration,the degradation of SMX first increased significantly,then increased slowly until unchanged;The degradation effect of SMX increased with the increase of p H value.PMS/PS promoted the dissolution of ozone from gas phase to liquid phase,which increased the concentration of ozone in liquid phase.The concentration of hydrogen peroxide in liquid phase had no significant difference under the three discharge systems;the SO₄·^-activated by PMS/PS promoted the concentration of·OH.（3）The existence of SO₄·^-and·OH in PMS and PS system was proved by electron spin resonance（EPR）;The free radical capture experiments of ethanol and tert butyl alcohol showed that SO₄·^-and·OH were significantly involved in the degradation process of SMX;the experiments of p-benzoquinone showed that the active substance O₂·^-produced by discharge played an important role in the degradation of SMX in the three systems;Nitrate ion capture experiments showed that hydrated electrons did not directly participate in the degradation of SMX,and CCl₄ could enhance the degradation effect of SMX.The results of TOC and LC-MS showed that after adding PMS and PS,the mineralization degree of SMX was higher and the decomposition of pollutants was more thorough,and the mineralization degree of PMS to SMX was higher than that of PS to SMX.