Study On Degradation Of Polyacrylamide Wastewater By Electro-Fenton Process

To meet the nation’s growing energy demand,the large-scale use of polymer flooding and alkaline/surfactant/polymer flooding on oil fields has been successfully in improving crude oil recovery.However,the residual polymers such as polyacrylamide（PAM）in the recovered water leads to high emulsification,small crude oil particle size and high suspended matter content in the recovered water,which is difficult to be treated by conventional water treatment processes in the oilfield to meet the demand of reinjection.Therefore,it is urgent to develop a new water treatment technology to treat the polymer-containing wastewater.Electro-Fenton advanced oxidation process is an ideal water treatment process since it can generate strong oxidizing hydroxyl radicals（·OH）to degrade pollutants non-selectively with less secondary pollution.To solve the problems of difficult catalyst recycling,strict p H requirement and low hydrogen peroxide（H₂O₂）generation rate in electro-Fenton process,a non-homogeneous electro-Fenton system with Co Fe₂O₄ as a solid catalyst and a gas diffusion electrode system were constructed in this experiment.The specific research includes the following points:1)A homogeneous Electro-Fenton system with graphite felt as the cathode and Ru-Ir/Ti electrode as the anode was constructed to investigate the feasibility of the system for PAM removal.The effects of the initial p H of the solution,current density and Fe²⁺dosage on the removal rate of PAM were investigated.The study showed that the homogeneous electric Fenton system could effectively remove PAM,and the PAM removal rate could reach 80.92%under the optimal conditions.The quenching experiments showed that·OH was the main specie for oxidative degradation of PAM,and then the species of reactive oxygen species in the system and their contribution were analyzed.The experimental parameters were optimized by response surface method,and the interaction between the factors was explored to obtain the optimal process parameters for PAM removal.2)The Co Fe₂O₄ catalysts were synthesized by the solvothermal method,and the physical phase composition,elemental valence distribution and surface functional groups of the catalysts were analyzed by XRD,XPS and FT-IR characterization.The effects of Co Fe₂O₄ dosage,p H and current density on the PAM removal rate were investigated.It was found that the non-homogeneous electric Fenton system had a superior performance for PAM removal,and the PAM removal rate was 11.09%higher than that of the homogeneous system under the same conditions.The stability of the catalyst was confirmed by recycling experiments and characterization,and the high PAM removal rate and stable structure were still achieved after 5 times of use.A possible mechanism of catalyst activation of H₂O₂ was proposed by analyzing the reactive oxygen species through free radical quenching experiments in the system and the change of elemental valence on the catalyst surface before and after the reaction.3)A porous gas diffusion electrode was prepared by roller pressing method,and the in situ H₂O₂ generation performance was investigated.The influencing factors of polytetrafluoroethylene（PTFE）content,p H and current density on the system were discussed.It was found that the concentration of H₂O₂ produced by the gas diffusion electrode system was 1478 mg/L,which was ten times higher than that of the graphite felt system;the gas diffusion electrode had the best H₂O₂ generation performance under neutral conditions,and PTFE could significantly affect the hydrophobic performance and interfacial transfer resistance of the electrode.The cycle use experiment and contact angle characterization proved that the electrode has good stability.Moreover,the gas diffusion electrode system showed superior PAM removal performance and could remove PAM thoroughly and quickly.