Remediation Of Volatile Organic Compounds Contaminated Soil By Activated Persulfate

Activated sodium persulfate (Na2S2O8) is a new type of oxidation agent in the field of soil remediation. In this paper, the degradation of 54 volatile organic compounds (VOCs) by activated sodium persulfate was studied in aqueous phase., The interaction among the oxidant, pollutants and soil matrix was examed focusing on the change of soil adsorption characteristics before and after SPS oxidation. Furthermore, batch experiments were carried out to simulate remediation of VOC contaminated soil by activated SPS. The results indicate that activated SPS oxidation is an economical, efficient and environment friendly technology for the treatment of VOCs contaminated soil.The results showed that:(1) With different activation methods, sodium persulfate can effectively degrade the VOCs in aqueous phase. Thermal activation yielded the best results compared with hydrogen peroxide activation, ferrous ion activation and alkali activation. Considering the high cost and difficulty of operation for application of thermal activation in a practical remediation project, we chose the more feasible ferrous ions activation method for further investigation in this experiment. The oxidation ability of sodium persulfate was significantly enhanced under ferrous ions activation and the degradation rate of the most compounds had improved. The degradation rate of 31 out of 54 compounds is 90% after 48h. Further, Complexing agents (Citric acid and EDTA) were added at a molar ratio of 5:1 (complexing agent to ferrous ion). The overall degradation rate of the compound follows the order:Na2S2Og-Fe(Ⅱ)/CA> Na2S2O8-Fe(Ⅱ)/EDTA> Na2S2O8-Fe(Ⅱ) >> Na2S2O8.The degradation of most VOCs demonstrates first-order kinetics, and the degradation rate of pollutants under different activation methods follows the order Na2S2O8-Fe(Ⅱ)/CA> Na2S2O8-Fe(Ⅱ)/EDTA> Na2S2O8-Fe(Ⅱ) the law.(2) Ferrous ion activated SPS are used to oxide two soil samples different soil organic matter (SOM) contents, and the adsorption behavior of toluene, chlorobenzene and naphthalene are examed before and after oxidation. The results show that activated SPS can oxidize humic acid and humin, and improve the adsorption capacity per unit SOM (in term of 1gKfoc). For soil 1, the oxidation effect of activation SPS on humic acid is significant, reducing the polarity of the SOM, thus increasing the adsorption capacity. For soil 2, the activated SPS can destruct the rigid structure of SOM, leading to linear adsorption.(3) We research the effects of citric acid chelated iron activated persulfate degradation the VOCs in soil. Experimental results show that the degradation rate of chlorobenzene and TCE is proportional to activator concentration, when the activator concentration was higher than 150 mg/L, the degradation rate had no significant improvement. And the concentration of persulfate was independent of the degradation rate since the dosage was much excess. We also investigated the oxidation of VOCs contaminated soil from a chemical site, which indicated that activated persulfate could be a effective treatment of the contaminated soil.