Study On Mechanism And Efficiency Of Tetracycline Degradation In Water By Carbon Based Electrocatalytic Membrane

Water resources are the material foundation and basic premise for human survival.However,due to the large application of antibiotics,the antibiotics pollution in aquatic environment is becoming seriously over the past few years.The antibiotics residual in aquatic environment will cause a series of serious problems like drug-resistant bacteria and chronic toxic effect,which may damage the ecological environment and human life.At present,the conventional methods to treat antibiotics wastewater such as adsorption and biological methods are not as effective as anticipated.Membrane filtration technologies like reverse osmosis(RO)and nanofiltration(NF)have been found to be with a good performance in removal of antibiotics in water.However,both RO and NF are energy intensive and suffering from severe membrane fouling.Therefore,it is a mandatory issue to develop alternative processes to remove antibiotics from the aquatic environments.Electrocatalytic membrane is a new water treatment technology coupling of electrocatalytic oxidation and membrane separation technology.Electrocatalytic membrane has shown the advantages of efficiency,flexibility and weak membrane fouling on treating organic contaminants in water,which improves the efficiency of organic degradation.Therefore,it deserves great value and realistic significance to study the treatment of antibiotics in water by electrocatalytic membrane technology.At present,the commonly used electrocatalytic membrane materials are coal based carbon,CNT,graphene,Ti4O7 and titanium.Compared with coal based carbon membrane(CM),the other materials like CNT,graphene,Ti4O7 and titanium membrane possess the disadvantages like complex preparation process and expensive,which hinder their large application in water treatment.Though the CM has the advantages of good conductivity,adjustable pore size and low cost,there are also some disadvantages such as low oxygen evolution potential and poor electrocatalytic activity.The electrocatalytic activity of CM could be significantly improved by surface modification technology.Tetracycline(TC),as a typical antibiotic,is one of the most used antibiotics and has been detected in different waters.Based on this,aquatic tetracycline is treated by CM which modified by nano catalyst.Thus provide a new and feasible method for treating antibiotics pollution in water environment.In this study,the preparation and properties of Ti O2/CM were first studied.The CM as basement membrane and tetrabutyl titanate as titanium source,CM supported with nano TiO2 catalyst was prepared by sol-gel method.TiO2/CM had certain adsorption capacity to tetracycline,and the flow rate had a great influence on the adsorption capacity of tetracycline.The breakthrough adsorption capacity of tetracycline by TiO2/CM was better under slow flow rate due to the longer contact time between tetracycline and TiO2/CM.The tetracycline breakthrough adsorption capacity by TiO2/CM was 2.425,2.312 and 2.144 mg/g while that of CM was 1.814,1.779 and 1.639 mg/g when the flow rate was 0.5,1.0 and 1.5 m L/min,respectively.The breakthrough adsorption capacity of tetracycline was increased by 33.7%,30.0% and 30.8% due to the larger specific surface area of TiO2/CM than that of CM.The tetracycline adsorption process by TiO2/CM and CM were both in accordance with Thomas model.Moreover,the breakthrough adsorption capacities were all in agreement with the experimental data.Under the electric field,the degradation of tetracycline was significantly improved owing to the better electrocatalytic activity of TiO2/CM.The removal rate of tetracycline by CM was 80.5% while that of TiO2/CM was as high as 93.8% under the same operation conditions.Furthermore,the factors affecting the removal of tetracycline by TiO2/CM were analyzed.The high removal rate of tetracycline could be achieved at low initial concentration and slow flow rate.The removal rate of tetracycline increased firstly and then decreased along with the increase of voltage while temperature had little effect on the removal rate of tetracycline.Secondly,the preparation and properties of Sb-SnO2/CM were studied.Stannous chloride and antimony chloride as raw material and CM as basement membrane,Sb-SnO2/CM was successfully prepared by sol-gel method.The optimum conditions for preparing Sb-SnO2/CM were as follows: the sol concentration was 0.3 mol/L,molar ratio of Sb: Sn was 1:10,coating times was 3 and calcination temperature was 600℃.The prepared Sb-SnO2 particles size was about 7.1 nm and uniformity distributed on the surface of CM through the chemical bond of C-O-Sn.The porosity of CM declined and the specific surface area of CM increased after surface modification by Sb-SnO2.The oxygen evolution potential,electrocatalytic activity and stability of the Sb-SnO2/CM were also improved.The Sb-SnO2/CM also had certain adsorption effect on tetracycline.The breakthrough adsorption capacity of tetracycline by Sb-SnO2/CM was 2.40 mg/g,which was higher than that of original CM.The removal rate of tetracycline by Sb-SnO2/CM was significantly higher than that of the original CM under the electric field.After 6 h operation,the removal rate of tetracycline by Sb-Sn O2/CM was still as high as 96.5% while that of was only 72.8%.Finally,the bacteriostatic circle method was carried out to demonstrate that the degradation products of tetracycline by Sb-SnO2/CM had no bactericidal effect on Staphylococcus aureus and Escherichia coli which means the degradation products have favorable biosafety.Then,the optimization of operating conditions for tetracycline degradation by carbon based electrocatalytic membrane was studied.Single factor experiments were studied to investigate the TOC removal efficiency in tetracycline solution and energy consumption along with voltage,flow rate,temperature and concentration as operating conditions.The results showed that the removal rate of TOC increased with the increase of voltage while decreased with the increase of flow rate and concentration.The energy consumption increased with the increase of the voltage and decreased with the increase of flow rate and concentration.In addition,temperature had little effect on the TOC removal rate and the energy consumption.In order to optimize the operating conditions,the influence of multi factors on the TOC removal rate and energy consumption were studied based on the single factor experiment results.According to Box-Behnken central composite design principle,the regression model of TOC removal efficiency and energy consumption were studied for tetracycline degradation by Sb-SnO2/CM by using response surface method.Then,a regression model was established based on the factors of voltage,flow rate,temperature and concentration.The variance analysis showed that the determination coefficient R2 of the regression model of TOC and energy consumption were 0.9885 and 0.9919,respectively.The high fitting degree of the model means it will have good fitting accuracy.The model reveales the interaction between multiple factors and can predict the operation conditions to achieve optimal TOC removal rate and minimum energy consumption.The optimum parameters of Sb-SnO2/CM for treating tetracycline were voltage of 3.07 V,flow rate of 1.5 m L/min,reaction temperature of 35℃ and initial concentration of 30 mg/L.Under these conditions,the removal rate of TOC was 84.5%,and the energy consumption was 33.50 kWh/kgTOC,which shows good agreement with the predicted values of TOC removal rate of 84.3% and energy consumption of 33.58 kWh/kgTOC.Finally,the degradation mechanism of tetracycline by carbon based electrocatalytic membrane was studied.As can be seen from the result of chronoamperometry,the flow model obviously improved the efficiency of mass transfer between electrodes and organic matters.The first order kinetic constants of tetracycline degradation by flow and batch model were 1.61 min-1 and 3×10-3 min-1.It is further proved that the flow model could improve the mass transfer rate.The process of tetracycline degradation by carbon based electrocatalytic membrane is the result of adsorption and electrochemical degradation.The adsorption rate of tetracycline on carbon based electrocatalytic membrane was improved because the external pump enhanced mass transfer process.Finally,tetracycline was degraded by direct and indirect oxidation.During the indirect oxidation process,H2O2 has little effect on the tetracycline degradation and ·OH radicals rather than ·O2-play the dominant role.In the process of tetracycline degradation,the intermediates were mainly decomposed by the loss of functional groups and ring-opening reaction during the electricalcatalytic oxidation process.Finally,the intermediates were degraded into CO2 and H2 O.In summary,on the basis of CM,the carbon based electrocatalytic membranes were prepared by using TiO2 and Sb-SnO2 as electrocatalysts which were used to degrade aqueous tetracycline.A multifactor regression model was established based on the experimental data.In addition,the process and mechanism of tetracycline degradation by carbon based electrocatalytic membrane were also analyzed.The above research investigated the effects of surface modification on the electrochemical and tetracycline degradation properties,explicated the effects of various operating conditions and their interactions on the tetracycline degradation and elucidated the process and mechanism of aqueous tetracycline degradation by carbon based electrocatalytic membrane.It will provide a theoretical basis and technical support for the treatment of real wastewater containing antibiotics by electrocatalytic membrane.