Degradation And Transformation Mechanism Of Residual Veterinary Drugs During Advanced Oxidation Process In Aqueous Matrices

There is a growing use of veterinary drugs in terms of the dosage, varieties and scope with the rapid development of China’s livestock industry. The extensive use of these additives causes a series of environmental problems, even harm the human body. Advanced oxidation processes can mineralize various robust micro-organic contaminants into carbon dioxide, water and other inorganics, so as to solve environmental problems fundamentally. Several typical veterinary drugs (sulfaquinoxaline sodium,3,5-dinitrobenzamide and thiampehenicol) used in livestock and poultry breeding were selected as the target contaminants, and the mineralization of sulfaquinoxaline sodium,3,5-dinitrobenzamide and thiampehenicol during advanced oxidation processes was investigated in this paper. The mechanism and the influence of environmental factors on the mineralization of these veterinary drugs during UV/H2O2 or UV/TiO2 oxidation processes were investigated.Sulfaquinoxaline sodiumin aqueous solution could be effectively degraded by UV/H2O2 oxidation process, which fits the model of pseudo-first-order kinetics. The influence of environmental conditions on the decomposition of sulfaquinoxaline sodium during UV/H2O2 systerm was investigated, the variation in total organic carbon (TOC) and the amount of the generated ions was determined, the intermediate products and the decomposition pathway were proposed according to the analysis of liquid chromatography with an ion trap and time-of-flight mass spectrometry (LCMS-IT-TOF). The decomposition of sulfaquinoxaline sodium via UV/H2O2 process was favorable under acidic and neutral conditions, but was inhibited under strong alkaline conditions (pH≥ 11). The presence of HCO3-, Cl- and NO3- ions were shown to have slight inhibition on the decomposition, but humic acids significantly decreased the decomposition rate.3,5-dinitrobenzamide in aqueous solution could be decomposed by UV/H2O2 and UV/TiO2 oxidation process. The decompositon of 3,5-dinitrobenzamide using UV/H2O2 and UV/TiO2 systerm fit the model of pseudo-first-order kinetics. The comparision of UV/H2O2 and UV/TiO2 processes for the decompositon of 3,5-dinitrobenzamide in aqueous solution was investigated. The variation in TOC and the amount of the generated ions were determined. The primary decomposition products of 3,5-dinitrobenzamide were identified using LCMS-IT-TOF. Based on these products, a possible decomposition pathway of 3,5-dinitrobenzamide during the UV/H2O2 and UV/TiO2 processes were proposed. The decomposition of 3,5-dinitrobenzamide in UV/H2O2 and UV/TiO2 processes was restrained under alkaline condition, but this inhibiting effect in the UV/H2O2 system was more obvious. The presence of inorganic anions ions had significant effect on the decomposition of 3,5-dinitrobenzamide, and the inhibiting effect on 3,5-dinitrobenzamide degradation followed the order of SO42-< Cl-< NO3-< HCO3-< CO32-. In addation, the UV/H2O2 process showed more inhibition than UV/TiO2 process.The decomposition of thiamphenicol in aqueous solution using UV/H2O2 process fits the pseudo-first-order kinetics model. In this paper, the influence factors of UV/H2O2 process on the decomposition of thiamphenicol were investigated. The release of Cl- and CH3COO- ions were detected in UV/H2O2 systerm. Under strong alkaline conditions, the decomposition of thiamphenicol in UV/H2O2 systerm was strongly inhibited, and this inhibition was mainly affected by the concentration of hydroxyl radical which influenced by environmental pH. The presence of Cl-, SO42-and NO3- ions in the environment had slight effect on the decomposition of thiamphenicol, but the presence of CO32- ion strongly decreased the decomposition rate. The UV/H2O2 systerm was suitable for treatment of thiamphenicol in natural water.