Effect Of Persulfate Combined With Nitrate To Remove Mono-aromatic Compounds In Karst Groundwater

In order to investigate the combined effect of In-situ chemical oxidation（ISCO）and Enhanced bioremediation（EBR）of carbonate rocks on the remediation of groundwater contaminated by gasoline,sodium persulfate（PS）was used as the chemical oxidant in this study,nitrate and sulfate were used as electron acceptors for biodegradation,and the persulfate was injected instantaneously/continuously in a box column with water-bearing limestone medium,to simulate and monitor the effect of chemical oxidation and bioremediation on the removal of benzene series（BTEX）at the site of a gasoline spill,and to observe the effect of persulfate oxidation on the hydrochemical environment,to evaluate the feasibility of the combination of chemical persulfate oxidation and enhanced bioremediation for benzenes.Through the instantaneous injection of persulfate experiment,the following conclusions were obtained:（1）In the box column flow rate was 391.3 m L/d hydrodynamic conditions,the removal effect of benzene series by PS was not obvious when the concentration of PS was 20 g/L,but the nitrate utilization rate reached 70%.When the concentration of PS was 250 g/L,the concentration of benzene series decreased by 61%within 2 days,and the removal rate was 6.9mg/L/d.When the hydraulic condition changed to still water,the removal rate increased to10.3 mg/L/d,and the removal effect was better.（2）The combination of PS chemical oxidation and nitrate reduction was possible.In Group A,the average concentration of nitrate in flowing water and static water were 29.9mg/L and 25.9 mg/L,respectively.But needed to further study the appropriate concentration of PS injecting,PS at high concentration had inhibitory effect on nitrate reduction.（3）The removal efficiency of benzene,toluene and xylene by chemical oxidation of persulfate in flowing water and standing water was better,and the removal rate of benzene was the highest,99%and 97%respectively,but it was not easy to be removed when the concentration of benzene was low When nitrate and sulfate were added alone,benzene（86%）and p-xylene（80%）were the highest in flowing and still water,respectively.（4）The concentration of Ca²⁺and HCO₃^-increased as a result of PS chemical oxidation,while ORP and EC increased,but it descend to the basic stable state in a short time.Through continuous injection of persulfate experiments,the following conclusions were drawn:（1）Continuous injection of PS was effective in removing benzene series and could effectively prevent the rebound phenomenon of pollutant concentration;during the continuous injection of PS,A1（tank outlet point）had a significant depletion of nitrate,and the average concentration was 27.1 mg/L,nitrate reduction occurred during the oxidation process.（2）The buffer action of the water-bearing medium of limestone could make the water environment p H neutral or slightly alkaline.In the process of chemical oxidation,the p H of water body varies from 6.6 to 7.6,which had little effect on microorganism.