Enhanced Electrokinetic Remediation Of Sulfamethoxazole Contaminated Soil By Green Tea Synthesized Nanoscale Zero Valent/Copper Activated Persulfate

Due to the excessive use of antibiotics in pharmaceutical,medical and other industries,China is facing serious environmental antibiotic pollution.Long-term abuse of antibiotics contaminated soil,water,food,and even produced drug resistance genes,which ultimately causes serious and irreversible damage to human health and the ecosystem.In this study,green tea extracts synthesized nanoscale zero valent/copper（GT-nZVI/Cu）activated persulfate（PS）enhanced electrodynamics（EK）was used to remediate sulfamethoxazole（SMX）contaminated soil.The effects of anolyte type,PS concentration and voltage gradient on SMX degradation were studied.The removal efficiency and content of SMX contaminated soil,the changes of soil physical and chemical properties and power consumption were evaluated,and the degradation mechanism of SMX in the system was analyzed.The specific conclusions of the study are as follows:（1）In GT-nZVI/Cu activated persulfate combined EK remediation,GT-nZVI/Cu suspension was innovatively used as an anolyte,and PS or H₂O₂ was added to it.When the voltage was 0 V/cm and GT-nZVI/Cu activated PS was used alone,SMX removal rate was36.87%.In the absence of GT-nZVI/Cu activation,PS could only remove 63.42%of SMX.Compared with H₂O₂ catalysis,PS activation has higher current,electroosmotic flow rate and SMX removal efficiency.Because SO₄^·-had shorter half-life,longer migration distance and selectivity than·OH,the experimental effect of adding PS was better than that of adding H₂O₂.（2）When using best technology of the voltage was 2 V/cm,the anolyte was 1.5g/L GT-nZVI/Cu suspension and 0.1 mol/L Na₂S₂O₈,the maximum removal rate of SMX reached94.09%,and the energy consumption was 297 k W·h·t^-1.The loss caused by adhesion and deactivation of GT-nZVI/Cu was effectively avoided by adding PS to GT-nZVI/Cu suspension.On the contrary,when PS was used as anolyte and GT-nZVI/Cu was added to it,the average removal rate of SMX was only 85.68%.（3）1.5 g/L GT-nZVI/Cu suspension as the anolyte could provide an activator to enhance the activation and decomposition of PS.Then adding 0.1 mol/L Na₂S₂O₈ to the system significantly improved the electroosmotic flow and removal rates of SMX.For the same concentration of GT-nZVI/Cu suspension,adding 0.1 mol/L PS solution could accelerate the corrosion rate of GT-nZVI/Cu material more than 0.05 mol/L PS,promote the formation of more SO₄^·-and·OH and improve the transport efficiency.In GT-nZVI/Cu activated persulfate combined EK process,applying a voltage gradient of 2 V/cm significantly increased the current intensity,resulting in the increase of electrolyte hydrolysis reaction rate and electroosmotic flow.The high voltage gradient has a positive effect on water transport and promotes the migration of soil solution,so S₂O₈^2-has a strong migration ability.Under the action of electric field,the electrokinetic effect is enhanced and the electrochemical oxidation is strong,which accelerates the removal of SMX.（4）The effect of electric field promoted the migration of oxidants and active radicals SO₄^·-and·OH produced by GT-nZVI/Cu activated PS in soil,and fully contacted with SMX.S₂O₈^2-can migrate throughout the soil chamber and eventually accumulate in the cathode electrolytic chamber.SO₄^·-and·OH also chemically degraded the highly hydrophobic organic matter SMX in situ,significantly increasing the removal efficiency.When the anolyte pH was less than 2,the dissolution of GT-nZVI/Cu accelerated and more Fe²⁺and Cu²⁺were produced.With the continuous decomposition of PS by activation of GT-nZVI/Cu,SO₄^·-and·OH synergistically oxidized and degraded SMX,showing a good degradation effect from 85.86%to 99.07%in soil cross sections from S1 to S5.（5）GT-nZVI/Cu activated PS enhanced EK technology can effectively remediate the surface,middle and bottom regions of each sampling point between the two electrodes.The average C/C₀ of sampling points in each layer was 94.11%,90.95%and 95.10%,respectively.The concentration of residual pollutants in the middle layer was generally higher,while the removal rate of SMX in the bottom soil was not significantly higher than that in the surface soil.The decrease of SMX in the bottom area was attributed to the higher moisture content and electroosmotic transport.However,the evaporation of water and the decreade of moisture content in the upper layer leaded to the weakening of SMX adsorption capacity,which could migrate and accumulate to the middle soil.