Study On Co-activation Of Potassium Persulfate By Ferrous Sulfate For The Removal Of Microcystis Aeruginosa

With global warming,the eutrophication of rivers,lakes and other water bodies has increased,and cyanobacterial blooms occur frequently.Cyanobacterial blooms not only pose a serious hazard to drinking water,but also have a negative impact on human production and health.Existing cyanobacterial bloom treatment techniques are not quite efficient in removing cyanobacterial cells,and the algal toxins released during the inactivation process can be potentially harmful to the quality of water sources.Therefore,it is necessary to find an efficient,safe and low loss treatment technology towards cyanobacterial bloom.In this paper,the effect of Na Cl O,K₂Fe O₄ and FeSO₄ on the removal of Microcystis aeruginosa cells in cooperation with potassium persulfate was investigated.Finally,the mechanism of algal cell removal by FeSO₄-PMS was investigated.The main research results are as follows.（1）FeSO₄-PMS combination was the most effective in removing Microcystis aeruginosa while causing the least adverse effects.FeSO₄-PMS was effective in removing algal cells while reducing turbidity and MC-LR concentrations.At a fixed PMS dosing rate of 0.1 mmol·L^-1,the algal cell removal rate,turbidity and MC-LR removal rate were 94.66%,3.8 NTU and 78.12%respectively at 120 min when FeSO₄ was dosed with 0.1 mmol·L^-1.At a Na Cl O dosing rate of 0.15mmol·L^-1,the algal cell removal rate,turbidity and MC-LR removal rate were62.86%,26.86%and 26.12%respectively.When K₂Fe O₄ was dosed at 0.05mmol·L^-1,the algal cell removal rate,turbidity and MC-LR removal rate were45.51%,14.68 NTU and 58.42%,respectively;in addition,Na Cl O-PMS and K₂Fe O₄-PMS had environmental risks such as excess chlorine residuals and residual Fe,respectively.The analysis showed that FeSO₄-PMS was more suitable for cyanobacterial water bloom treatment.（2）The alkaline environment and inorganic ions(HPO₄^2-,Cl^-,HCO₃^-and NO₃^-)adversely affected the removal of algal cells by FeSO₄-PMS.As the initial p H increased,the algal cell removal rate gradually decreased to 97.37%,95.69%,94.25%,92.48%and 89.79%when the p H 6.0,7.0,8.0,9.0 and 10.0,respectively.HPO₄^2-,Cl^-,NO₃^-and HCO₃^-ions consumed the SO₄^-·and·OH radicals in the system through a competitive mechanism,but there was An inhibitory effect found on the removal of algal cells by FeSO₄-PMS during the investigation.（3）Using FeSO₄ dosing rate,PMS dosing rate and rotational speed as response values,the optimal parameters for algae removal by FeSO₄-PMS were obtained using the response surface methodology（RSM）,in which FeSO₄ and PMS dosing rate were both 0.102 mmol·L^-1 and rotational speed was 309 r·min^-1.Under these conditions,the predicted value of algal cell removal was 94.78%and the actual value was 94.91%,and the accuracy of was 99.87%.（4）FeSO₄-PMS could effectively degrade algal-derived organic matter（AOMs）with fluorescence characteristics in the solution of Microcystis aeruginosa,and the green and yellow fluorescence intensity decreased sharply or even disappeared in theⅠ,ⅡandⅣspectral regions,indicating that microbial metabolites and humic acid substances can be effectively degraded.When FeSO₄and PMS were both dosed at 0.1 mmol·L^-1,with the increase of FeSO₄ dosage,the removal rates of algal cells,DOC and UV₂₅₄ were 94.66%,58.92%and41.52%,respectively,and the zeta potential decreased to a minimum of 0.33 m V.（5）The reasons for the efficient removal of algal cells are oxidation and flocculation.On the one hand,FeSO₄ catalyzed the decomposition of PMS to produce a large amount of SO₄^-·and·OH,which oxidatively degrades the AOMs in the solution,on the other hand,the Fe³⁺was formed by oxidation effectively neutralizes the negative charge on the surface of algal cells,and the net zeta potential was continuously reduced.In addition,the contribution of the oxidation and flocculation stages to the removal of algal cells was 30.50%and 69.50%,respectively,and SEM analysis showed that there was no large-scale lysis of algal cells before and after treatment.In summary,FeSO₄-PMS can remove Microcystis aeruginosa from water in an efficient,safe and low loss manner,and has a wide application prospect in the field of cyanobacterial water bloom treatment.