Reseach About Removing PFOA And FC-95 From Wastewater By Electrocoagulation Using Iron Electrode

Perfluorinated compounds(PFCs) are the typical emerging contaminants, in which perfluorooctanoic acid(PFOA) and perfluorooctane sulfonic acid potassium salt(FC-95) are the widely concerned substances because of their highly stable chemical properties, easy bioaccumulation and strong toxicity. Exploring the efficient methods to remove PFOA and FC-95 has become a new hot focus in the field of international environment technology. The electrocoagulation method using iron electrode possess electrostatic adsorption ability and floatation function simultaneously. Moreover, the method can generate iron floc in-situ, which possessses higher flocculation activtity than the conventional chemical flocculant. Therefore, this thesis investigated the efficiency of the electrocoagulation method using iron electrode to remove the PFOA and FC-95 in aqueous. The effects of influential factors on the removal rate of PFOA and FC-95 during the electrocoagulation process were examined including current density, initial p H in solution, rotor speed, hydrogen peroxide dosage, anion types and so on. And their reaction mechanisms were also ananlysised during the electrolysis and electrocoagulation.This experiment first studied the effect to the removal of PFOA from wastewater by electrocoagulation using iron electrodes under different Current density, initial solution p H, rotational speed, the way of adding hydrogen peroxide, plate distances, plate material and additives. the electrocoagulation reacted 90 minutes, the removal rate of PFOA increased with the increase of current density, when the current density increased from 6.25 m A/cm2 to 37.5 m A/cm2, the removal rate of PFOA quickly rose from 38.14% to 98.01%, then the continuing increase of current density did little influence to the removal of PFOA, The influence of initial p H in solution to the removal of PFOA from wastewater by iron electrocoagulation was little, when the initial solution p H was 3.77 and 9.10, the removal rate of PFOA were 97.38% and 92.90%, the removal rate under other p H were near to them. Rotor speed had a great influence on the removal of PFOA from wastewater by iron electrocoagulation, when the rotor speed was 5 r/s, the removal rate was the best, because rotor speed could make great difference to the iron floc spatial form. In the result of this experiment, the way of adding hydrogen peroxide could have a obvious effect on the removal of PFOA by iron electrocoagulation,from the experiment we could see that when the dosing interval of hydrogen peroxide was 20 minutes, and adding 0.5m L every time, the removal rate of PFOA was the highest, up to 96%. The plate distances had a little influence on the removal of PFOA, this experiment chose 2cm as the plate distance. As to plate material, we could see from the the result of experiment, Fe plates were more beneficial than Al paltes to the removal of PFOA by iron electrocoagulation,the removal rates of PFOA about Fe plates and Al plates were 90% and 40% in the same experiment condition, so in the following experiment, we used Fe paltes as electrodes to deal with PFOA in wastewater. Finally, additives were also reseached in order to remove PFOA totally, As the result of experiment showed, gelatin was the additive the experiment needed.Then this experiment studied the effect of current density, rotational speed, the way of adding hydrogen peroxide, anion types, cation types and plate material to the removal of FC-95 from wastewater by electrocoagulation using iron electrodes. Result showed that the influence was similar to the removal of PFOA, but the removal time was shorter. The experiment reacted 50 minutes, in a certain range, the removal rate of FC-95 increased with the increase of current density, when the current density increased from 6.25 m A/cm2 to m25 m A/cm2, the removal rate of FC-95 quickly rose from 37.13% to 97.02%, then the continuing increase current density did little influence to the removal of FC-95. Rotor speed between the range of 5 r/s to 9 r/s was effective to the removal of PC-95, presenting a board mass transfer zone. In addition, the promotion of hydrogen peroxide to the removal of FC-95 was not obvious. When none of hydrogen peroxide adding, the removal rate of FC-95 was 84.48%, after adding hydrogen peroxide the removal rate of FC-95 had a slight increase, adding 0.2 m L hydrogen peroxide per 25 minutes, the the removal rate of FC-95 was up to 90.84%。Moreover, the common anions in the wastewater, such as Cl-, SO42-, NO3- had influence to the removal rate of FC-95 as well. As we could see from the results of experiment, Cl-, SO42- had positive effect to the removal of FC-95, and NO3-had negative effect to the removal of FC-95. Those were because of these anion could influence charge distribution on the flocs surface, thus effecting the removal rate of FC-95. In addition, the experiment studied the effect of Ca2+、Mg2+、Ni2+、Cu2+、Cr3+to the removal of FC-95,results showed that, Ca2+ had positive effect to the removal of FC-95, Mg2+、Ni2+、Cu2+and Cr3+had negative effect to the removal rate of FC-95. In the end, the experiment studied the effect of plate material to the removal of FC-95, results showed that, Fe plates were more beneficial than Al paltes to the removal of FC-95.Finally this thesis discussed the mechanism about the removal of PFOX by electrocoagulation using iron electrodes and its practical technologies of the iron electrode processing. Electrostatic adsorption and hydrophobic adsorption were the main function between ferric floc and PFOX. As to electrode technologies, removal rate and energy consumption of electrocoagulation removing PFOA without dealing plates was best contrast with polishing plates and acid pickling plates. Electrode conversion was not helpful to the removal of PFOA.When power supply mode was working 20 minutes and stopping 5 minutes thr energy consumption was lower than power supply not stopping, with the removal rate of PFOA almost did not change. And Fe-Al electrodes had the highest removal rate and lowest consumption.Research shows that the removal of PFOA and FC-95 from wastewater by electrocoagulation using iron electrodes is effective, the relevant research results can provide theoretical support and technical reference to the effectively dealing with industrial perfluorochemicals of wastewater through electrocoagulation.