Experimental Study On Degradation Of Organic Pollutants In Groundwater By Persulfate With Carbonylated Activated Carbon Catalyst

The discharge of refinery waste water,waste residue,waste gas(three wastes)and accidental leakage will inevitably lead to a large number of organic pollutants into the soil,resulting in groundwater pollution in the refinery and its surrounding areas.Compared with traditional chemical oxidation technology,persulfate advanced oxidation technology has the advantages of low cost,high efficiency and wide range.However,due to the low decomposition rate of persulfate at room temperature,the oxidation reaction rate is slower.Therefore,the selection of appropriate persulfate catalysts to optimize their activation mode and improve their degradation efficiency of target pollutants has become one of hot spots in the development of this technology.First,a method for simultaneous determination of five organic pollutants(toluene,ethylbenzene,p-xylene,nitrobenzene and aniline)in groundwater by high performance liquid chromatography(HPLC)has been developed.By adjusting parameters such as mobile phase,flow rate and ultraviolet wavelength,the linear range,precision,recovery and detection rate of the method were tested.Secondly,based on coconut shell as raw material,a method for preparing carbonylated activated carbon(AC)has been explored by carbonization,activation,regulation and other steps,and it was characterized by X-ray diffraction,BET surface area and scanning electron microscope.In a variety of single factor experiments,the adsorption and catalytic properties of the target catalyst were investigated,and the optimal oxidation reaction conditions were obtained.Finally,this study tried to detect the degradation of persulfate activated by the catalyst by free radical inhibition experiment and electron paramagnetic resonance(EPR)and reasonably inferred the degradation pathway of the target pollutant in the reaction process.In these results,HPLC could be used for sensitive and accurate analysis of five organic pollutants in groundwater.The linear detection range of the five organic pollutants ranged from 0.05 to 100 mg/L,and the correlation coefficients were all greater than 0.999.Moreover,the standard concentration of 50 mg/L and 100 mg/L samples were used to verify the method.The standard recovery rate was in the range of 91.1%?104.4%,and the relative standard deviation(n=5)was 1.0%?3.4%.By comparing AC obtained by oxidation regulation at different annealing temperatures,we found that the target catalyst prepared at 650?annealing temperature had the optimal activity.In the degradation process of organic pollutants,under the conditions of 0.5 g catalyst,20 mg/L the initial concentration of organic pollutants and the initial slightly acidic,there were the optimal adsorption performance.The adsorption process was in accordance with the quasi-secondary kinetics(R²>0.99).In addition,the catalytic effect could be the best,under the conditions of 0.5 g catalyst,0.2 g persulfate,and the initial neutral pH.Considering that the removal rate of organic pollutants could reach 50%in the third reuse,and the removal rate of organic pollutants could return to 70%after high temperature regeneration,the target catalyst had good reuse performance and regeneration performance.Based on EPR experiments and relevant literature,we concluded that carbonylated activated carbon could activate persulfate through surface carbonyl as the active site,promote its decomposition into sulfate radical and hydroxyl radical,and thereby oxidize and remove organic pollutants in groundwater.The degradation pathways of the five organic pollutants mainly include:1)a series of intermediate products formed by electron transfer between the target pollutant and sulfate radical or hydroxyl radical;2)the intermediate product is further oxidized by sulfate radical or hydroxyl radical into small-molecule substances(such as carboxylic acid);3)eventually mineralized into CO₂ and H₂O.