Removal Of Tetracycline In Simulated Water By Plasmas With Three Kinds Of Power Supplies

As a new advanced oxidation technology in waste water treatment,plasma treatment attracts lots of attention in recent.In plasma treatment process,the particle bombardment,including energetic electrons and ions,the reactions of active free radicals(such as hydroxyl),ozone and hydrogen peroxide with the organic,and irradiation of ultraviolet,all will degrade pollutants.The advantages of plasma treatment are non-selectivity,high efficiency,no secondary pollution(or less),higher efficient decomposition of organic molecules,and room temperature and atmospheric pressure process.Generally,no external reagents are added in the whole process.In this thesis,the simulated antibiotic tetracycline wastewater was treated by dielectric barrier discharge(DBD)plasma,which driven by three kinds of power sources.The main research contents are as follows:(1)The design of a novel plasma treatment system.The system consists of power supply and reactor.The coaxial cylinder dielectric barrier discharge(DBD)reactor is adopted,which generates a strong electric field benefiting to the direct interaction of plasma with the liquid.With the circulation of water,furthermore,the mass transfer between the species in plasma and pollutants in water is much efficient.The dielectric covered on the electrode avoids arc discharge,and the electrolysis and Joule heat effects during discharge.We mainly focus on comparison of the high-voltage-pulse power supply and the medium-frequency-continuous power supply,where the pulse power supply can provide a narrow rise/fall edge and short pulse width,which it is thought to easily form high-energy electrons.In addition,some plasma diagnostic equipment are equipped to monitor plasma parameters in real-time.(2)A coaxial cylinder DBD plasma can effectively degrade tetracycline in wastewater.The effects of process parameters on the removal efficiency of tetracycline were studied experimentally,including power waveforms,peak voltage,frequency,pulse width and discharge gas.It was obtained that the removal rate of tetracycline was up to 90%,the removal rate of chemical oxygen demand was in the range of 45 ~58%,and the maximum energy efficiency was up to 5.3g/kWh when the tetracycline pollutant was treated for 10 min.Besides,it was found that the reaction fellow the first-order reaction kinetics.(3)The reaction mechanism of organic matter degradation of in plasma.The free radicals in gaseous plasma were detected by on-line optical emission spectroscopy(OES).The hydroxyl radicals,the strong oxidant,was detected in the plasma which is believable to play critical role in the TC degradation after combining with results of the use of hydroxyl radical inhibitors in water.The treated water was analyzed by means of ultraviolet-visible spectrophotometer,pH meter,COD analyzer,conductivity meter and liquid chromatography-mass spectrometry.It was found that at the beginning 2 min plasma treatment or 5 min after plasma discharge treatment the reaction mechanism was quite different.At the beginning the radicals interacted with tetracycline molecules to degrade the main chain,the molecular structure of tetracycline was cracked in a short time and new substances(N-de-dimethyl-4-epi-tetracycline,anhydrotetracyclin,etc.)were appeared.After 5 min,the formed active radicals by plasma reacted with the middle substances in the liquid,the degradation was continued along with the discharge time,until the tetracycline was almost completely degraded to the inorganic.