Effect Of Fe²⁺ Activated Persulfate Combined With Bioremediation In Removing Gasoline BTX From Karst Groundwater Under Water-flow Condition

In the remediation of fuel oil contaminated groundwater,the combination of in situ chemical oxidation that based on persulfate（PS）with bioremediation technology was a recommended strategy,beside PS can be activated by Fe²⁺to obtain more powerful oxidation ability.In order to better understand the performance and feasibility of Fe²⁺activation in the combination of PS chemical oxidation with bioremediation,and the dissolution characteristics of gasoline and the effect of nitrate in karst limestone water-bearing medium.This study was performed that used the box-column devices filled with limestone and karst groundwater.The effect of Fe²⁺activated PS combined with bioremediation was studied for the treatment of benzene,toluene and xylene（denoted as BTX）in gasoline contaminated karst groundwater.Gasoline was injected to simulate the contaminated environment and nitrate was added to enhance biodegradation.PS was injected and activated by Fe²⁺as required to carry out chemical oxidation under water-flow condition.The results indicated:（1）The concentration of BTX showed multi-peak fluctuations and tailing characteristics due to continuous dissolution after gasoline infiltrated into groundwater,with the order of toluene>benzene>o-xylene>m-xylene>p-xylene.The dissolved concentration of toluene was larger,reached 72.3%in group A and 70.2%in Group B,which had absolute superiority in the total concentration of BTX.（2）Nitrate supplementation can reduce the release of dissolved BTX.The highest BTX mass fluxes of A1 and B1 were 38.339 and 41.472 mg/d,respectively,and the peak concentrations were 24.501 and 21.102 mg/L respectively,during the second injection of gasoline with continued nitrate supplementation.The peak concentration of BTX rebound after nitrate supplementation was discontinued,which were 39.891 and 48.682 mg/L,and the mass fluxes were 62.421 and 76.178 mg/d in the third gasoline injection.（3）The Fe²⁺activation significantly enhanced the degradation of BTX.During the experiment,the pseudo first-order decay rates of BTX in the activation group and the non-activation group were 0.031～0.070 d^-1and 0.027～0.052 d^-1 respectively.The combined application of chemical oxidation and enhanced bioremediation showed a stronger degradation effect of BTX compared with in situ chemical oxidation alone.Under the condition of nitrate supplement,the BTX pseudo first order attenuation rate was 0.026～0.070 d^-1,which was higher than that under the condition of stopping nitrate supplement was 0.020～0.036 d^-1.（4）The Fe²⁺activation technology had the potential to be applied to the combined remediation of BTX in karst environments.In the process of chemical oxidation,DO was used by microorganisms in the groundwater water-bearing medium,nitrite as an intermediate of denitrification was detected at a concentration range of 0.1～2.0 mg/L.（5）The buffering of limestone made the p H of water environment approach neutral,ranged from 6.86 to 7.59,which also caused the increasing of Ca²⁺and HCO₃^-concentrations by PS chemical oxidation.The erosion of carbonate limestone by activation was more severe,and the highest concentration of Ca²⁺in the activation group was 279.5 mg/L during the experiment.