Tannic Acid Enhanced Persulfate For Degradation Of Chlorinated Hydrocarbons

Chlorinated hydrocarbons is a common type of soil and groundwater contaminants,which have carcinogenic,teratogenic,mutagenic and other biotoxic effects.Therefore,how to efficiently degrade chlorinated hydrocarbon pollutants has attracted more and more attention.In this paper,tannic acid（TA）activated persulfate（PS）system was used,two typical chlorinated hydrocarbon pollutants,chloroform（CF）and trichloroethylene（TCE）,were used as degradation objects to evaluate the degradation effect of the activated system.Explored and optimized the relevant factors that affect the degradation reaction.The main research contents are as follows:（1）Degradation of chloroform using tannic acid and alkaline co-activated persulfate.The degradation effect on CF by PS and different activation systems（PS/TA,PS/Na OH and PS/TA/Na OH）were investigated,and the effects of PS concentration,Na OH concentration,TA concentration and reaction temperature on the degradation of CF were also studied.The free radical quenching experiment was used to identify the type of free radicals in the reaction system,and a possible activation mechanism was proposed.Furthermore,the effects of ions（Cl^-,HCO₃^-and NO₃^-）and humic acid（HA）that may exist in actual groundwater on the degradation effect of PS/TA/Na OH system were explored;and this system was tested on actual contaminated groundwater samples.The results show that the PS/TA/Na OH system has excellent degradation performance for CF.The degradation percentage of100mg/L CF can reach 99%after 160min under the conditions of PS=100m M,Na OH=0.4M,TA=400mg/L and 25℃.It is find that superoxide radicals（O₂·^-）and hydroxyl radicals（·OH）play an important role on the degradation of CF in this system.Cl^-and HCO₃^-can both reduce the degradation efficiency of CF,while NO₃^-has no effect on the degradation efficiency of CF,and HA can promote the degradation of CF.（2）Degradation of trichloroethylene using persulfate activated by tannic acid chelated ferrous iron.The degradation performance of TCE by different reaction systems(PS,PS/Fe²⁺,PS/Fe²⁺/TA)was compared,and the effect of PS concentration,Fe²⁺concentration,TA concentration,p H and reaction temperature on the degradation of TCE were examined.The types of free radicals in the reaction system were identified by free radical quenching experiments.Furthermore,the effects of ions（Cl^-,HCO₃^-and NO₃^-）and humic acid（HA）that may exist in actual groundwater on the degradation effect of PS/Fe²⁺/TA system were explored;The results show that the PS/Fe²⁺/TA system can effectively degrade TCE,and the degradation percentage of 55mg/L TCE can reach 99%after 60min under the conditions of PS=15m M,TA=80mg/L,Fe²⁺=0.6m M and 25℃.There are mainly·OH and sulfate radicals（SO₄·^-）in this system,and SO₄·^-contributes more to the degradation of TCE than·OH.HCO₃^-in groundwater has the greatest effect on the degradation of TCE,with high concentrations HCO₃^-,the degradation percentage of TCE will decrease significantly;the other two ions have little effect on the degradation of TCE;and HA has a certain promotion effect on the degradation of TCE.