Study On Process Mechanism And Application Of Microbial Electro Fenton Coupled Sodium Persulfate System For Degradation Of Perfluorooctanoic Acid

Perfluorooctanoic acid（PFOA）is an extremely difficult organic pollutant to degrade.With the wide use of its products（such as non stick pot coating,waterproof membrane,corrosion-resistant pipeline,etc.）,PFOA gradually diffuses into the environment and accumulates in organisms.Its pollution control is imminent.Microbial electro Fenton technology is a new decontamination technology.Combining traditional Fenton technology with microbial fuel cell,it can generate H₂O₂ in situ and produce a large number of hydroxyl radicals（·OH）with strong oxidation under the catalysis of Fe²⁺,which can be used to oxidize organic pollutants.As a strong oxidant,sodium persulfate is also commonly used in the treatment of various organic pollutants.It usually needs thermal activation,UV activation,metal ion activation and other ways to produce sulfate radical（·SO₄^-）with strong oxidation.Considering that the hydroxyl radical has no activity on PFOA,this paper will use the combination of microbial electro Fenton and sodium persulfate oxidation,and use the sulfate radical as the switch to turn on the degradation process of PFOA,so as to make the hydroxyl radical participate in the degradation process.Firstly,the feasibility of degradation of PFOA by the coupling system is proved by experiments;Then,in order to achieve the best degradation effect of PFOA,the influencing factors such as temperature,voltage and p H are explored in the coupling system to determine the best operating conditions;Finally,because the output of hydrogen peroxide is one of the limiting factors of PFOA degradation,this paper further improves the performance of microbial electro Fenton system by modifying the cathode material,so as to achieve better treatment effect.The results obtained in this paper are as follows:（1）It is proved that the microbial electro Fenton coupled sodium persulfate system is feasible to degrade PFOA.Firstly,in the microbial electrochemical reactor without Fe²⁺,the concentration of PFOA hardly decreased under open circuit and closed circuit conditions,indicating that the adsorption and electroadsorption effects of cathode on PFOA are limited;Further comparing the degradation effects of PFOA in independent microbial electro Fenton reactor,single sodium persulfate oxidation reactor and microbial electro Fenton coupled sodium persulfate reactor,the degradation rates are 12.5%,84.0%and 95.5%respectively.The results show that it is difficult to effectively degrade PFOA only through the oxidation of hydroxyl radical.Persulfate is the key to the disconnection of carbon fluorine bond of PFOA,and the coupling of the two can show stronger oxidation ability,Thus,it has more advantages in the degradation of PFOA.（2）The influencing factors such as temperature,applied voltage,initial p H of cathode and initial concentration of PFOA are optimized,and the mechanism of their influence on the coupling system is described.The optimal operating conditions are as follows:temperature 40℃,applied voltage 0.8 V,initial cathode p H 3,Fe²⁺8 m M,cathode ventilation rate 15 m L/min.Under the optimal conditions,the degradation rate of PFOA can reach 95.8%,the defluorination rate is 93.2%,and finally only 2.1 mg/L PFOA is left.Through the qualitative and quantitative analysis of intermediate products by LC-MS,the degradation path of PFOA in the system was explored.（3）The cathode material was modified.In order to further accelerate the degradation of PFOA by increasing the output of hydrogen peroxide in the system,a catalyst is used to modify the cathode material.It has been found that MOF（metal organic mineralized material）has a wide range of applications in electrocatalysis.Therefore,in this paper,a variety of MOF materials are selected for carbonization to make catalysts,and the cathode graphite plate is modified.Firstly,the effects of 88-Fe,100-Fe,100-Fe and 53-Fe/Mn catalysts obtained by carbonization at 600℃on the degradation effect were investigated.The catalytic effect of 100-Fe was the best,reaching 99.9%degradation rate after 96 hours,and finally PFOA was only 0.0045 mg/L;Secondly,the effects of carbonization at 600℃,800℃,900℃,1000℃and non carbonized 100-Fe on the degradation effect were investigated.The results showed that the catalytic effect of 600℃-100-Fe was the strongest,and carbonization at too high temperature could not play a catalytic role,and even hinder the reaction.