Study On The Purification Of Microcystin-LR And Its Degradation By Electrocatalysis Oxidation

Frequent outbreaks of algal blooms and the aggravation of harmfulness induced by its secondary metabolism products-microcystins(MCs) have directly threatened the safety of human drinking water. So,technologies for MCs removal have been the hot spot in current research.Electrocatalysis which is easy to control,simple to operate and has no secondary pollution,has obtained more and more attention.This paper established an economic and effective method,which was composed of extraction and common-pressure column chromatography,to purify MCLR.Through measuring the variation of Microcystin-LR(MCLR) concentration and the change of solution characteristics in the process of electrocatalysis oxidation,we studied the effectiveness and influence factors of MCLR degradation by electrocatalysis oxidation using Ti/RuO₂ anodes.Then we analyzed the intermediate products during purified MCLR degradation by electrocatalysis oxidation.Finally we did preliminary research into the processes of anodic reaction using cyclic volt-ampere method and probed into the reaction kinetics.A new effective method to purify MCLR was established in this paper.We found that the combination of hexane extraction→solid phase extraction(SPE)→Sephadex LH-20 gel filtration→DEAE Sepharose CL-6B anion exchange chromatography purified MCLR well and could obtain purified MCLR with purity above 90%and the recovery of MCLR was about 65%.The result showed that the effect of MCLR degradation by electrocatalysis oxidation was quitely good.When the current density was 4mA/cm²,MCLR concentration was deeply decreased with the hydraulic detention time of 14min and the initial concentration of MCLR being 40μg/L.As the hydraulic detention time increased to 40min,the removal rate of MCLR could reach 100%. Study on the influence factors of MCLR degradation demonstrated that hydraulic detention time, current density and initial concentration of MCLR had important effect on MCLR degradation and removal.Increasing hydraulic detention time,raising current density and reducing initial concentration of MCLR all benefited MCLR degradation.The type of electrolyte had some effect on MCLR degradation:the effect in Na₂SO₄ electrolyte was better than that in phosphate buffer,and the effect in phosphate buffer was better than that in NaNO₃ elecyrolyte.Ion intensity and flow rate had little effect on MCLR degradation and removal.The result of research into intermediate products of purified MCLR degradation by electrocatalysis oxidation showed that the peptide ring of MCLR could be changed,the main toxic group Adda moiety could be destructed and the intermediate products were mainly small molecular organic acid and also included a small part of amino acid and phthalate which could be completely removed through extending treated time.There were no virulent byproducts during the reaction.From the result of cyclic volt-ampere behavior of MCLR on anode,we concluded that MCLR diffused to the interface of Ti/RuO₂ anode/solution and gradually oxidized by·OH or other oxidative group.The degradation of MCLR by electrocatalysis oxidation conformed to pseudo-first-order-rate reaction kinetics equation.