Removal Of Halogenated Steroid Glucocorticoid From Aqueous Solution By Calcium Peroxide:Efficiency And Mechanism

Nature and synthetic glucocorticoids（GCs）of water environment pollution are frequently reported all around the world in the recent ten years,which become the frontier research field of international environment.Very low concentration of glucocorticoid exposure can cause biology appear a series of physiological disorder,such as immune response inhibition,growth inhibition,and physical deterioration,etc.However,due to the attention of glucocorticoid is still in its infancy,the relevant glucocorticoid environmental behavior research is still lacking.In this study,Performance of calcium peroxide（CaO₂）in removing glucocorticoid contamination was investigated with triamcinolone acetonide（TA）as the representative target compound.The effect of different experiment parameters（CaO₂ dosage,initial TA concentration,and solution pH）on their degradation by CaO₂ Oxidation was studied and the degradation mechanism in CaO₂ Oxidation process was explored.An experimental design based on the surface response methodology was applied to assess the individual and interaction effects of several operating parameter on the treatment efficiency.Based on the experimental data,the role of reactive oxygen species（ROS）in TA degradation was tested.Specifically,TA degradation intermediates during CaO₂ oxidation were detected by UHPLC-QTOF and the change of GC toxicity during TA degradation was deduced according to the intermediate structures.The main results were as follows:（1）Effects of CaO₂ dosage,initial TA concentration,and solution pH were investigated.A pseudo-first-order kinetic model was used to describe the TA degradation during CaO₂ oxidation.The results showed that TA removal efficiencies increased with the increase of CaO₂ dosage and initial TA concentration.Higher removal efficiencies were achieved at initial pH values of 6.8 and8.6.An experimental design based on the surface response methodology was applied to assess the individual and interaction effects of several operating parameters（CaO₂ dosage,initial pH value,reaction time,and glucocorticoid concentration）on the treatment efficiency.The degradation of TA model is that:Y=-67.04+26.59×A+16.11×B+6.57×C+963.9×D-1.25×AB-0.48×AC+103.16×AD-0.18×BC+22.75×BD-27.14×CD-2.91×A²-1.03×B²-0.09×C²-8502.08×D².Based on the experimental design data,the optimal conditions were obtained as follows:CaO₂ dosage at4 g/L,initial pH=5.7,and reaction time=15.7 min.Moreover,additional experimental result obtained under optimal conditions（82.8%）was found to be very close to the predicted value（88.6%）.（2）Effects of 5 anions contained in water matrix on TA removal during CaO₂ oxidation were evaluated.The results showed that HCO₃^-,Cl^-,and NO₃^-had inhibitive effects on TA degradation while SO₄^2-had no effect and PO₄^3-had promotive effects.Humic acid（HA）had positive influence on TA removal which could be attributed to its obvious effects on adsorption.（3）The role of reactive oxygen species（ROS）in GC degradation was tested by electron paramagnetic resonance spectroscopy（EPR）.Further confirmed that the ROS released by CaO₂（HO·and·O₂-）are the main factors contributing to TA removal,among which HO·radicals play the most important role.（4）The adsorption effects of CaO₂ particles during CaO₂ oxidation were verified using SEM-mapping of CaO₂ particles before and after oxidizing methyl orange.The adsorption effects of CaO₂ decreased with the increase of reaction time.The results showed that the comprehensive effects of adsorption and active surface sites led to the decrease of TA removal rates.（5）TA degradation intermediates during CaO₂ oxidation were detected by UHPLC-QTOF and the change of GC toxicity during TA degradation was deduced according to the intermediate structures.Six intermediates were revealed during TA degradation for the first time.Possible intermediate structures and degradation mechanisms of TA during CaO₂ oxidation were proposed.The degradation intermediates showed that the epoxidation of the double bond,the oxidation of ester and acetal groups at the D-ring,and the dehalogenation（defluorination）of the B ring occurred during CaO₂ oxidation of TA,which indicated the decrease in GC activity.The results showed that CaO₂ treatment can be a practical and effective technology for removal of GC and decrease of GC toxicity.