TW80 and GLDA-enhanced oxidation under electrokinetic remediation for aged contaminated-soil: Does it worth?

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Soil from a former chemical plant was found to be contaminated with organochlorine compounds (OCs) from aged pesticide residues and underwent surfactant-enhanced electrokinetic remediation (EKR). Tween 80 (TW80) and N,N-Dicarboxymethyl glutamic acid tetrasodium (GLDA) were used to increase the availability of OCs and to enhance oxidation efficiency in the soil under EKR. The results indicate that flushing soil with TW80 increased the removal of persistent OCs from the soil, with 40%–80% removal efficiency. Further, incorporating TW80 with sodium persulfate significantly advanced oxidation and removed 60%–82% of OCs (in both absence and presence of the nZVI reactive barrier) within 10 days. Compared to control treatment, the addition of TW80 improved EKR by 20%–30%. The improvement was attributed to the ability of TW80 to solubilize hardly-soluble compounds and to sustain the activation of persulfate ions (S2O82−) by dissolving metal ions in the soil that would stimulate the production of sulfate radicals (SO4•−) and thus the degradation of pollutants (in the absence of nZVI reactive barrier). Differing from TW80, GLDA’s capacity to solubilize and extract OCs from the soil was much lower and less reliable, averaging around 10% compared to 60% OC-removal for TW80. However, in the absence of oxidant activators from an external source, GLDA was important for sustaining the Fenton reaction. Its inclusion increased pollutant removal from an average of 50%–60%. The addition of the nZVI reactive barrier did not significantly improve remediation within 7 days. These findings suggest that TW80 combined with EKR and advanced oxidation in the presence of the nZVI reactive barrier is the best in situ approach to remediate soils contaminated with OCs from chemical waste of industrial processes.