Efficiency And Mechanism Of Sonoelectrochemical Oxidation In The Treatment Of Aged Landfill Leachate

The characteristics of poor biodegradability and strong toxicity of landfill leachate make it difficult for conventional biological treatment methods to achieve ideal treatment effects.However,advanced oxidation processes that can generate strong oxidative free radicals are considered to be a promising technical means for treating this type of wastewater.With the continuous strict improvement of environmental legislation in China,how to realize the economical and effective treatment of such wastewater is still the focus of current research.In view of the current research status of landfill leachate treatment technology,this work prepared a new type of modified lead dioxide anode and used it in the combined process of ultrasonic and electrochemistry,in order to improve the treatment effect of landfill leachate and reduce the reaction energy consumption of the system.A titanium-based lead dioxide electrode containing the PANI-α-Pb O₂intermediate layer and PDMS-Ce-β-Pb O₂ active layer was prepared by the convenient two-step electrodeposition method.The characterization results of SEM and XRD show that,compared with the traditional Ti/Pb O₂ electrode,the Ti/PANI/PDMS-Ce-Pb O₂ electrode has a smaller crystal size（44.8 nm）and denser surface morphology.The test results of BET are consistent with the analysis results of SEM and XRD.The modified Ti/PANI/PDMS-Ce-Pb O₂ electrode has a larger specific surface area of 0.2783 m²/g,which means that it can provide more reactive sites for the degradation of organic pollutants.LSV and EIS exhibit that the oxygen evolution potential of the electrode after modification was improved（1.91 V vs.SCE）,while the electrochemical impedance was effectively reduced（39.5Ω）,which is beneficial to reduce the occurrence of oxygen evolution side reactions and speed up the mass transfer.In addition,Ti/PANI/PDMS-Ce-PbO₂ electrode showed excellent electrocatalytic performance in the electrochemical degradation of gallic acid,which proved that the modified electrode has considerable industrial application potential.The Ti/PANI/PDMS-Ce-PbO₂ electrode was used in the sonoelectrochemical system to oxidize the aged landfill leachate.Through the design of orthogonal experiments and single factor experiments,the influence of three key operating parameters:current density,initial p H,and ultrasonic power were investigated.The results demonstrate that the current density plays a dominant role.Under the optimized conditions:the current density of 42 m A cm²,the initial p H of 6,and the ultrasonic power of 50 W,the sonoelectrochemical system achieved 61.9%and 91.8%removal rates of COD and chroma in the landfill leachate,respectively.And it was also found that the biodegradability of landfill leachate was significantly improved（the value of BOD₅/COD increased from 0.026 to 0.314）.UV-vis and GC-MS were used to analyze the changes in the water quality of landfill leachate after the sonoelectrochemical oxidation.The raw water mainly contained a large amount of esters,siloxanes,and heterocyclic substances,while the effluent after 2 h reaction was mainly composed of carboxylic acids and ketones with relatively simple molecular structures.To further improve the processing efficiency of the landfill leachate,PMS was introduced into the sonoelectrochemical system.The feasibility and superiority of the activation of PMS by ultrasound synergistic electrochemistry method were discussed.Compared with the EC/PMS system,the US-EC/PMS system has higher FA degradation efficiency and current efficiency.While compared to the US-EC system,the US-EC/PMS system completed more FA removal and reduced energy consumption.All the results indicate that the effect of sonoelectrochemical activation of PMS is satisfactory.The results of scavenger experiment and EPR show that hydroxyl radical,sulfate radical,and singlet oxygen were all reactive oxygen species generated in the system.Accordingly,the possible mechanism of sonoelectrochemical activation of PMS on FA degradation was proposed.Three-dimensional fluorescence analysis showed that most of the humic substances（Hss）were effectively removed,proving that this technology is a powerful means to treat organic wastewater contaminated by Hss.