Study On Degradation Of Metronidazole By Thermally Activated Persulfate System

Metronidazole(MNZ),a nitroimidazole antibiotic derivative,is commonly applied in clinical to prevent and treat infectious diseases caused by a wide range of bacteroides,anaerobic bacteria,and protozoal diseases.Moreover,MNZ is used as an additive in fish and poultry feed to eliminate parasites.Thus,MNZ always accumulates in animals,fish farm water,and wastewater from meat processing industries.Recently,advanced oxidation technology based on sulfate radials has widely used to degrade refractory organic pollutants in wastewater.In comparison with hydroxyl radicals,sulfate radicals,with higher oxidative potential,are more efficient in degrading organic matter,sulfate radicals,which are of longer half-life period and high stability,can react completely with organic matter and degrade organic matter at a higher reaction rate.Because of the high solubility,oxidative potential and stability,persulfate(PS)commonly serves as a precursor that leads to sulfate radicals formation.In this paper,MNZ degradation by thermal activated persulfate(TAP)was studied.The main research contents and results are as follows:(1)This paper investigated the performance of TAP on MNZ removal under different conditions including temperature,initial solution pH,PS dosage,initial MNZ concentration,and common components in water(chloride,bicarbonate and humic acid).The results show that MNZ degradation is fitted well with pseudo-first-order reaction kinetics(R~2>98.8%)under these influence factors.The rate constant of MNZ degradation increases with the initial dosage of PS,as well as the temperature.The degradation rates of MNZ is also fitted well with the Arrhenius equation under the influences of temperature,the activation energy calculated is 100kJ/mol by the fitting equation.The rate constants of MNZ degradation decreases with the increases of the concentration of contaminants and common components in water.(2)Based on the single factor experiments,Box-Behnken Design(BBD)of Response Surface Methodology(RSM)was used to optimize experimental conditions of MNZ degradation,and the experimental results were fitted with a quadratic polynomial.The variance analysis results show that the quadratic polynomial model is meaningful.The correlation coefficient of model(R~2=0.9989)showing that experimental value and predicted value of MNZ degradation ratio are of good consistency.(3)The mechanism of MNZ degradation by TAP was studied.Sulfate radicals and hydroxyl radicals were identified as the major predominant free radicals by the electron paramagnetic resonance(EPR)spectrum in this system,and radicals quenching study revealed that sulfate radicals was mainly responsible for MNZ removal.The mineralization of MNZ reached more than 97.2%during the 10 h reaction process.It was established and verified that the kinetic model of MNZ degradation by TAP under the optimal condition.The model conforms to the pseudo-first-order reaction kinetic.