Research On Effect And Influence Factor On Sulfamethoxazole Pollution Control Via Modified Clay In Seawater

With the increasing abuse of antibiotics in mariculture in recent years,antibiotic pollutants and red ride disaster in mariculture have brought serious harm to water quality safety and product health,and even threatened the sustainable development of the industry.Faced with the widespread problem of antibiotic pollution in seawater,effective treatment methods are urgently needed.Although the methods of antibiotic pollutants in urban water and wastewater have been widely studied,the characteristics of seawater,such as high salinity and richness in various ions and microorganisms,causing the lack of effective methods of antibiotic control in seawater so far.Modified Clay（MC）is an environmentally friendly material that can effectively control red tide,but there is a lack of focused research on its effectiveness in controlling antibiotic pollutants.In order to ensure the healthy and sustainable development of mariculture,safe and effective synergistic treatment methods are urgently needed for the frequent occurrence of antibiotic pollution in mariculture.In this study,sulfamethoxazole（SMX）was used as the antibiotic model pollutants,and heterosigma akashiwo was used as the representative microalgae of red tide outbreak in cultured water.The treatment efficiency of three types of modified clays against SMX was compared.A type of modified clay（Fe-PMS-MC）with effective SMX control was selected after the addition of Fe（Ⅱ）to the selected peri-monosulfate（PMS）oxidation composite modified clay.And then the main characteristics of seawater and the effects of heterosigma akashiwo on SMX removal efficiency were analyzed.The mechanism of Fe-PMS-MC on SMX control was explored,and the application method of Fe-PMS-MC was further optimized.It provided a green and effective method for the treatment of antibiotic pollution in seawater.（1）The efficiency difference of varied modified clays in SMX removal was compared,and the modified clay which could control SMX effectively was selected.The effects of modified clay,such as inorganic modified clay,organic modified clay and oxidized composite modified clay,which are commonly used for red tide control,were tested on SMX removal.It was found that the oxidized composite modified clay with peroxymonosulfate（PMS）as the oxidant had the highest removal rate of SMX.Transition metal Fe（Ⅱ）was introduced into PMS-MC to form Fe-PMS-MC complex,and the SMX treatment ability was further improved.The effect of the ratio of PMS and Fe（Ⅱ）in Fe-PMS-MC on the SMX removal efficiency was further compared by single factor experiment,and the optimal ratio of Fe-PMS-MC was determined as Fe（Ⅱ）:PMS:MC=0.135:0.15:1.0（g:g:g）.When the dosage of Fe-PMS-MC was 1.0g/L in the optimal ratio,the SMX removal rate reached 90.3%within 6 h.Therefore,Fe-PMS-MC is a kind of modified clay which can effectively control SMX in water.（2）The factors influencing the SMX removal by Fe-PMS-MC were analyzed in seawater conditions.In order to optimize the application method of Fe-PMS-MC in the treatment of SMX pollution in seawater,experiments tested the effects of the main characteristics of seawater,such as temperature,initial pH,salinity and inorganic anions,as well as the effects of heterosigma akashiwo and AOM on the effect of SMX control.The SMX removal rate increased from 28.6%to 77.9%within 6h as the temperature increased from 25 to 55℃.Initial pH in the range of 3.0-9.0 had no significant influence on the SMX control,while the SMX control was inhibited significantly at pH11.0.With the increase of salinity from 0‰to 35‰,the SMX removal rate increased from 40.1%to 75.6%within 6h.The SMX control efficiency was significantly improved by the addition of three inorganic anions,Cl^-,HCO₃^-,and SO₄^2-,respectively.There was essentially no effect of heterosigma akashiwo at 10³and 10⁵ cells/m L algal densities on SMX control,in contrast AOM promoted the SMX control in the concentration range from 5.40 mg/L to 21.61 mg/L.By combining the effects of various factors in seawater,Fe-PMS-MC was applied to seawater and found to be more effective in the SMX control in seawater compared to freshwater.Also Fe-PMS-MC was highly effective in the control of heterosigma akashiwo and which was completely removed at a dose of 0.2 g/L.（3）The action mechanism of Fe-PMS-MC was investigated in the SMX control in seawater.The experiments tested that the change pattern of PMS and Fe（Ⅱ）content in Fe-PMS-MC is similar to that of SMX,indicating that the main roles in the treatment of SMX include the strong oxidation of PMS and the activation of Fe（Ⅱ）.The main active species of Fe-PMS-MC are·OH,SO₄^-·and ¹O₂,so its action process on SMX mainly consisted of the radical oxidation pathway dominated by·OH and SO₄^-·,and the non-radical oxidation pathway dominated by ¹O₂.Environmental factors affected SMX removal by influencing radical oxidation and non-radical oxidation of Fe-PMS-MC.The increase in temperature produced more SO₄^-·and·OH by promoting the breaking of asymmetric peroxide bonds in PMS.In contrast,the high pH（≥11.0）converted SO₄^2-to SO₅^2-with lower oxidation and inhibited the conversion of O₂ to ¹O₂.The addition of some inorganic anions such as Cl^-,HCO₃^-,and SO₄^2-,improved the SMX removal efficiency.The phenolic groups from AOM could activate PMS to form ¹O₂ to remove antibiotics.By studing the addition sequence,times and time interval of Fe-PMS-MC for removing SMX,it was found that adding PMS-MC first and then adding Fe（Ⅱ）was the best addition sequence.The SMX removal rate was higher with more times of addition,and the shortest SMX removal time was at the addition time interval of 5 minutes.