Study On Remediation Of PCBs From Contaminated Site Soils By The Combination Between Soil Washing And Homogenous Fenton-like Oxidation

Polychlorinated biphenyls (PCBs) are a class of synthetic persistent organic pollutants,which has carcinogenic, teratogenic and mutagenic effects. Among environment, the most ofPCBs are presented in soil due to the low water solubility and volatility. In PCBscontaminated soil remediation methods, the chemical method has been widely used with fastand efficient repairment rate at home and abroad compared with physical and biologicalmethods, especially Fenton reagent oxidation.Fenton reagent oxidation, an advanced oxidation technology, is often used to oxidizecontaminants fastly, which utilized a large amount of hydroxyl radicals produced in solutionof hydrogen peroxide (H2O2) with an iron catalyst in acidic conditions. Because of traditionalFenton system has some disadvantage, such as low utilization of H2O2, oxdizible of Fe2+, nofully mineralization of organic contaminates and so on, more and more studies improve thismethod by using Fe3+, ultraviolet, microwave and ultrasound with the deepening of researchand form Fenton-like reagent oxidation. Among Fenton-like oxidation, the combination ofFe3+and H2O2is a typical method, using Fe3+replace Fe2+to react with H2O2is a prosperousFenton-like reagent oxidation method with the reason that it can not only reduce the cost ofreaction, but also fully mineralize organic contaminates. However, due to PCBs could closelyabsorb organic matter in soil environment and their low water solubility, the way to increasethe water solubility of hydrophobic organic contaminants is a key of remediation of PCBscontaminated soil. As we all know, surfactant as an excellent soil washing solution is oftenused to remedy organic contaminated soil of high concentration by increasing water solubilityof hydrophobic organic contaminants. Concerning the specificity of remediation of PCBscontaminated soil, the combination technology by soil washing and Fenton-like reagentoxidation is used in this study.On the base of the reported studies, batch experiments were performed to investigateeffects of four elution solvents (Brij58， Brij30, Tween-80and2-hydroxypropyl-beta-cyclodextrin) on solubilization and elution of PCBs from transformerlandfill contaminated soils collected from Ningbo in this study. The study choose PCB28as arepresentative pollutant and optimize Fe3+-H2O2of degradation conditions for PCB28inFenton-like system. Finally, the optimized Fe3+-H2O2of Fenton-like system was used todegrade PCB28in surfactant. The main conclusions are as follows:1. Results showed that Brij58was the most effective eluant among four elution solventsin washing PCBs from contaminated soil. Elution efficiencies of PCBs is60%, respectively, when contaminated soil was extracted by Brij58at10g/L,25℃and pH4.5after one timeelution.2. Optimization of the feasibility of PCB28degradation in a homogeneous Fenton-likesystem:①The homogeneous Fenton-like system composed of ferric ion and hydrogenperoxide has significant degradation of low concentrations of PCB28(100ppb). Afterreaction of9h, the efficiency of PCB28degradation was96%under the best reactioncondition that was composed of50mmol·L-1H2O2and500μmol·L-1Fe3+at pH3and25oC.②The efficiency of PCB28degradation was inhibited by the addition of inorganic ion, whichfollowed with an order of PO––43﹥SO42﹥Cl–﹥ClO–4﹥NO–3.③The efficiency ofPCB28degradation also decreased with increasing concentration of acetone and OH was thereactive species during the degradation of PCB28in a Fe3+-catalyzed Fenton-like system withthe reason that there was no degradation of PCB28in the presence of tert-butanol added as aquenching reagent of OH.④One monochlorobiphenyl, three dichlorobiphenyl, and twohydroxytrichlorobiphenyl were identified as major products of PCB28degradation.3. The degradation of PCB28in elution solvents by homogeneous Fenton-like system:①The homogeneous Fenton-like system composed of ferric ion and hydrogen peroxide hasthe best degradation rate of low concentrations of PCB28(100ppb) in10g L-1Brij58. Afterreaction of9h, the efficiency of PCB28degradation was64.05%under the best reactioncondition that was composed of50mmol·L-1H2O2and500μmol·L-1Fe3+at pH3and25oC.②After reaction of9h, the degradation efficiency of PCB28(10ppm) was42%under theoptimized reaction condition that was composed of50mmol·L-1H2O2and5mmol·L-1Fe3+atpH3and25oC by homogeneous Fenton-like system composed of ferric ion and hydrogenperoxide.③After reaction of9h, the degradation efficiency of PCB28(286ppm) in highconcentration elution solvents was34.58%under the optimized reaction condition that wascomposed of50mmol·L-1H2O2and5mmol·L-1Fe3+at pH3and25oC by homogeneousFenton-like system composed of ferric ion and hydrogen peroxide.