Catalytic Ozone Degradation Of Sulfamethoxazole In Wastewater Enhanced By High-Gravity

Sulfamethoxazole（SMX）is a broad-spectrum type of sulfonamide antibiotic,which has a significant impact on the ecological environment because of its strong environmental persistence,difficulty in biodegradation,carcinogenicity,teratogenicity and mutagenicity.The conventional wastewater treatment methods are not ideal for the removal of SMX from wastewater.As an advanced oxidation technology,catalytic ozone oxygen method can generate more oxidizing hydroxyl radicals（·OH）,which can effectively solve the problem of incomplete degradation of organic matter in water treatment,and has the advantages of no secondary pollution is widely used in the field of water treatment.However,ozone as the commonly oxidant in this method has the disadvantages of low solubility in water and low ozone utilization rate.Based on the better mass transfer characteristics of high-gravity technology,the catalytic ozone degradation of sulfamethoxazole in wastewater enhanced by high-gravity was proposed.This paper presents the high-gravity technique to catalyze the ozone oxidation of SMX in wastewater using metal ions as catalysts and to investigate its degradation effect.Using SMX as the target pollutant,different metal ions were used as catalysts in an aeration reactor（BR）to investigate the effect of ozone-catalyzed degradation and to seek the best metal catalysts;the effect of operating parameters on the enhanced ozone degradation for the removal of SMX in a high-gravity environment with the best catalyst was also investigated.Finally,tert-butanol was introduced as·OH trap to further investigate the mechanism of SMX degradation,and the intermediate products of SMX degradation were detected by liquid chromatography-mass spectrometry（LC-MS）,and the possible degradation pathways of SMX were inferred from the intermediate products.The main research contents and results are as follows:（1）The degradation rate of SMX(η_SMX)was 74.66%and the removal rate of TOC(η_TOC)was 22.92%when using ozone oxidation alone to treat SMX wastewater.There was a problem of lowη_TOC during ozone oxidation of SMX,so metal compounds were added to the system as catalysts to improve its mineralization rate.The catalytic effects of metal salts on SMXη_SMXandη_TOC were cobalt salt,cerium salt,manganese salt,copper salt,iron salt,and nickel salt in descending order.Among them,cobalt salt has the best catalytic effect on ozone-catalyzed degradation of SMX wastewater.And the second metal was selected for two-component catalysis with cobalt salt,and the best catalytic conditions were finally screened as follows:the total metal ion concentration C_TOT was 1.2 mmol/L,the copper-cobalt bimetallic component was catalyzed,and the copper-cobalt ratio was 1:3,and theη_SMX was 98.69%and theη_TOC was78.35%at 60 min of catalytic reaction.The ozone utilization rate（R_u）measured in BR was36.02%for the ozone oxidation system alone（BR-O₃）and 51.16%for the catalytic ozone oxidation system（BR-Cat-O₃）,neither of which had high R_u.Therefore,the high-gravity enhancement technique was chosen for better ozone transfer and decomposition,and for better use of ozone..（2）To investigate the efficiency of high-gravity enhanced catalytic ozone degradation of SMX in a rotating packed bed（RPB）.The optimal operating conditions were optimized for involving an O₃ initial concentration(C_O3)of 30 mg/L,a liquid flow rate（Q_L）of 80 L/h,an initial p H of 5.8,and a high-gravity factor（β）of 30 under the initial SMX concentration of 50mg/L.In the RPB,theη_TOC was 77.64%with 25 min of reaction.Comparing theη_TOC in BR and RPB under similar experimental conditions,theη_TOC in RPB was enhanced by 24.02%for the same reaction time（25 min）compared to using the BR reactor;the reaction time in RPB was reduced by 15 min for similarη_TOC.In RPB,the R_u for the catalytic ozone oxidation system（RPB-Cat-O₃）had a R_u of 85.84%,which was 34.68%higher than that of BR-Cat-O₃ system,and was 31.19%higher than that of RPB-O₃ system.The comparison shows that the catalytic ozone oxidation technology enhanced by high-gravity technology has a significant effect on the mass transfer of ozone,which is beneficial to improve the mineralization of organic matter.（3）The free radicals in the system were captured by free radical capture experiments using tert-butanol,and theη_SMX was reduced by 26.43%,and then the signal peak of·OH was detected by electron spin resonance spectrometry（EPR）,which proved that the system followed the·OH mechanism.And ten intermediates in the catalytic degradation process were detected by LC-MS,and three possible degradation pathways were inferred based on the intermediates:hydroxylation of benzene ring,breakage of S-N bond and ring opening of isoxazole ring,through which SMX was mineralized to CO₂,H₂O,etc.