Experimental Study On The Degradation Of Chlorpyrifos By A Three-dimensional Electrode-electric Fenton Method

Organophosphorus pesticide wastewater has a complex composition,poor biodegradability,high toxicity and is harmful to the environment,so it can have a devastating impact on the ecological environment if not treated properly.The three-dimensional electrostate-electric Fenton coupling method is a highly efficient advanced oxidation method,which occupies a small area with a large treatment capacity,can remove difficult organic pollutants quickly and efficiently,and has low energy consumption and low price,and can effectively treat difficult organic substances.Therefore,this thesis investigates the degradation mechanism of chlorpyrifos using the commonly used organophosphorus pesticide chlorpyrifos as an example,using the 3D-Electro-Fenton system.The current three-dimensional electro-Fenton method is mainly through the addition of Fe²⁺and H₂O₂to form the Fenton reagent,and then combined with the three-dimensional electrode system together to degrade wastewater,however,this common method requires the addition of a large number of chemicals,in practice,if the ratio is not well mastered will not only increase the power consumption and increase the cost of treatment,but also easy to cause a reduction in treatment efficiency.Therefore,this study uses iron carbon particles as particle electrodes and uses them to form tiny primary cells to become the third electrode,allowing them to precipitate Fe²⁺and then generate H₂O₂through cathodic aeration,thus forming Fenton’s reagent.This approach does not require the addition of chemicals and the iron carbon particles can be reused,making it more economical and practical.In this paper,chlorpyrifos simulated pesticide wastewater was selected for degradation,and the removal of chlorpyrifos by a three-dimensional electro-Fenton system was investigated using chlorpyrifos as the target pollutant.The optimal operating conditions of the three-dimensional electro-Fenton system were investigated using single-factor experiments and orthogonal tests,and the composition of the reaction substrate,the surface changes of the particle electrodes and the composition of organic matter in water were determined by liquid chromatography,liquid chromatography-mass spectrometry（LC-MS）,scanning electron microscopy（SEM）and energy spectrometry（EDS）,the main findings from this investigation into the degradation mechanisms of chlorpyrifos are as follows.（1）Comparing three materials,activated carbon fibre,stainless steel and nickel foam,as cathode materials.The results show that the removal rate of COD_crand organic phosphorus from wastewater is high with stainless steel.The optimal operating parameters of the three-dimensional electrode-electro-Fenton system were optimised as follows:current density of 16m A/cm~2,pole plate spacing of 5cm,iron-carbon particle filling amount of 600g/L and initial pH=3.When the electrolysis time is 20min,the removal rate of COD_crcan reach 93.7%and organic phosphorus can reach 95.9%.The removal rate of organic phosphorus was 95.9%;through the orthogonal test,it can be seen that the degree of influence of each factor in the system is initial pH>iron carbon particle filling quantity>aeration quantity>current density.（2）Comparing the removal effect of iron carbon micro-electrolysis process,three-dimensional electrode and three-dimensional-electric Fenton system on wastewater,it can be seen that the three-dimensional electric Fenton system has the highest removal efficiency,with a maximum removal rate of 94.3%for COD_crand 96.5%for organic phosphorus,and the three-dimensional electric Fenton system costs less than 4.7 yuan per kg of COD of wastewater treated under the best conditions.（3）The analysis of the degradation pathway and reaction mechanism of chlorpyrifos by a three-dimensional electrode-electro-Fenton system showed that the P=S bond of chlorpyrifos becomes a P=O bond,which is desulfurized and oxidized to form CPO,and then degraded to small molecules by hydrolysis,dechlorination and substitution;SEM scanning,EDS and energy spectroscopy of the reaction substrate on the surface of the iron-carbon particles,presumably with flocculation of aluminium and iron ions in the reaction.Determination of iron ions in solution demonstrates the presence of both homogeneous and non-homogeneous Fenton reactions in the system;hydroxyl radical quenching experiments illustrated the relationship between the concentration of tert-butanol and the removal of COD_cr,and the results showed that hydroxyl radicals had a major role in the degradation of chlorpyrifos.（4）The number of reaction stages under optimum conditions was explored using COD_cras an indicator,and finally it was shown to be in accordance with the primary reaction kinetic model,with the primary reaction kinetic equation being:y=0.1472x-0.1238 and R~2=0.9904 in accordance with as well as the reaction kinetic equation.And the first level kinetic decay model was established as C_t=1530.33xe^-0.12516twith a reaction rate constant of 0.12516 and a correlation of 0.9903.