Synergistic Effect Of Catalysts On Aqueous Gemfibrozil And Norfloxacin Degradation Combined By Dielectric Barrier Discharge Plasma

Pharmaceuticals and personal care products?PPCPs?have received a great attention due to their extensive used and long-term threat to the ecological environment and human health.Gemfibrozil?GEM?is a triglyceride-regulated medication to treat coronary disease and improper disposal contaminates the environment.Given to the widely detected of GEM in municipal effluents and surface water around the world,and the low efficiency of removal via waste water treatment plants,it is essential to design effective techniques to remove GEM,and biodegradation is less efficient when dealing with the refractory and toxic organisms.Norfloxacin?NOR?is a member of fluoroquinolones?FQs?family,which exhibits high antimicrobial activity in viro-against a wide variety of gam-negative and gram-positive bacteria.Due to the tolerance,persistence of NOR,the removal of NOR by conventional water treatment technologies is generally inefficient.Hence,there is an increasing demand for developing more effective ways to remove such antibiotics from waters.Dielectric barrier discharge plasma?DBD?is a kind of advanced oxidation technology which integrates ultraviolet radiation,ozone oxidation and hydroxyl radical oxidation.The produced ultraviolet light and active material can react with the target organic pollutants in water,resulting in the fully mineralized to CO₂ and H₂O.DBD has been widely studied by domestic and foreign scholars and has broad application prospects.The gas-liquid DBD plasma is characterized by optical emission spectroscopy?OES?and the concentration of reactive species?RS,such as H₂O₂,O₃and NO₃^-?are measured with spectrophotometer which increased with the discharge time.This study researched the potential degradation effect and efficiency of the DBD/catalyst system on GEM and NOR and try to elucidate the degradation mechanism.The CNTs/?Fe₂O₃ catalyst is combined with DBD to degrade GEM.The CNTs/?Fe₂O₃ is prepared by liquid precipitation and characterized by X-ray diffraction?XRD?and transmission electron microscope?TEM?.The catalytic property,effects of the discharge power,and initial concentration on the GEM degradation rate and the energy efficiency are determined.Compared to the sole gas-liquid DBD plasma treatment for 2 minutes,addition of CNTs/?Fe₂O₃ to the gas-liquid DBD plasma reactor improves the degradation rate of GEM by 30.5%.Moreover,a possible reaction pathway was proposed based on the intermediates identified by mass spectrometry?MS?.All these results confirmed that DBD/CNTs/?Fe₂O₃ might be an appropriate method for effective degradation of GEM in waters.Various discharge voltages,initial pH values as well as two catalysts H₂O₂ and Fe²⁺were applied.Both H₂O₂ and Fe²⁺at low concentration were observed contributing to the improvement on the degradation rate,while restraint would occur at high concentration.10 mg/L Fe²⁺+DBD system was found the optimized condition to achieve the maximum degradation rate 99.0%after 60 s.Mineralization efficiency of NOR was measured by TOC analyzer and 84%TOC was removed after 4 min of discharge at 60.3 W in 10 mg/L Fe²⁺+DBD system.Possible degradation mechanisms of NOR were proposed,where the defluorination,the cleavage of piperazine ring and quinolone ring was considered the major degradation pathways,leading the DBD/catalyst system to be an effective and promising pharmaceutical wastewater treatment method.