Enhanced electrokinetically-delivered persulfate and alternating electric field induced thermal effect activated persulfate in situ for remediation of phenanthrene contaminated clay

Delivering persulfate (PS) efficiently into clay is an unsolved challenge. This study proposes a novel strategy with enhanced electrokinetically -delivery PS into clay by using PS for continuously flushing cathode to inhibit water electrolysis at cathode electrode. On this basis, a novel approach of heating soil by alternating current (AC) was used to thermally activate PS in situ. Results show that the mass transfer efficiency of PS by electroosmotic flow is about 20 times that by electromigration. Moreover, when PS was added in the anode chamber, using PS solution continuously flushing cathode created a relatively balanced the influent and effluent flow rates, significantly improving the mass transfer efficiency of PS. Compared to using NaNO3 solution flushing, a significant increase of 51.7% was achieved, reaching 78.8%, for the phenanthrene (PHE) average degradation rate in soil cell. In contrast, the best overall PHE removal rate was observed, reaching 87.8%, by a cycle strategy of enhanced electrokinetically -delivered PS followed by AC heating applied. Electron paramagnetic resonance spectroscopy analysis showed oxidative radicals (SO center dot 4 /center dot OH) were the major species responsible for enhanced PHE degradation. These results demonstrate that this cycle strategy is a viable method for remediation of polycyclic aromatic hydrocarbons in clay.

Automated summary

A novel strategy was proposed to enhance the delivery of persulfate into clay by continuously flushing the cathode with persulfate, while using alternating current to thermally activate the persulfate in situ. The results showed significant improvement in mass transfer efficiency and pollutant degradation rate, demonstrating the effectiveness of this cycle strategy in remediating polycyclic aromatic hydrocarbons in clay.