Stability Of Persulfate In Karst Groundwater And Its Removal Effect On Benzene Series

In situ chemical oxidation（ISCO）is an efficient and convenient technology to remove organic pollutants from the medium,and it has been widely used in the remediation of organic pollution of petroleum hydrocarbon-contaminated groundwater and soil.In order to better understand the feasibility of the application of ISCO technology in karst underground river,this study has taken the groundwater in karst conduit polluted by gasoline as the research object,used persulfate（PS）as the chemical oxidant,and used the carbonate conduit model in the laboratory.Under the hydraulic condition of the total conduit flow of 120 m L/h.The stability experiment of persulfate in karst conduit and the oxidation repair experiment of persulfate on benzene series of gasoline in karst conduit were carried out respectively to investigate the migration and stability of PS with different concentrations in karst conduit.To evaluate the oxidation removal effect of activated/inactive PS on benzene-series（BTEX）of gasoline in karst conduit under flowing/still water condition and the influence of chemical oxidation on hydrochemical characteristics.After analyzing the experimental results,the following conclusions were drawn:（1）PS has good stability and strong migration ability in unpolluted karst conduit.In a conduit with a length of 3.67 m and a flow rate of 1.08 m/d,the mass recovery rates of 5 g/L（low）and 10 g/L（medium）concentration of PS recoveries were 74.6%and 84.3%,respectively;The PS of 20 g/L（high）concentration was decomposed to some extent in the conduit,but it still had good stability,and the mass recovery rate was 75.7%.The average migration rates of PS at the three concentrations respectively were 0.85 m/d,0.96 m/d and1.22 m/d.（2）When the mole ratio of PS:BTEX is 18,PS can effectively remove BTEX in the groundwater of the karst conduit.Under flowing water condition,the concentration of BTEX in effluent water decreased from 62.3 mg/L to 33.3 mg/L,the reduction of BTEX per unit time was 4.14 mg/h;under still water condition,the reduction of BTEX per unit time is 0.60mg/h;The decay of BTEX concentration follows the quasi-first-order reaction kinetics equation,and the decay rate constant of BTEX is 0.0056 h^-1in the flow state,under still water condition,the decay rate constant of BTEX is 0.0029 h^-1;PS has a good oxidation effect in the karst conduit and the removal effect of BTEX under flowing water condition is better than that under still water condition.（3）Fe²⁺activation can enhance the oxidation of PS and improve the oxidation removal effect of BTEX.When the mole ratio of PS:Fe²⁺was 4:1 and the mole ratio of PS:BTEX was18:1,the BTEX concentration in the effluent water decreased from 60.3 mg/L to 23.1 mg/L,and the reduction and attenuation coefficient constants of BTEX per unit time respectively were 4.60 mg/h and 0.0071 h^-1.（4）The PS oxidation process will lead to the decrease of pH value in the water from 7.9to 7.5,promote carbonate karst erosion,increase the concentration of calcium ions in the water,sulfate concentration and dissolved oxygen concentration also increase with the reaction process,and improve the redox potential and electrical conductivity of the water.Fe²⁺activation causes a large amount of decomposition of PS.After activation,the pH value of water decreases from 8.0 to 6.9,more sulfate group is produced,and the electrical conductivity and REDOX potential are higher.The oxidation process of PS after activation has a greater impact on the hydrochemical characteristics.