Effect and mechanism of persulfate activated by different methods for PAHs removal in soil

•Oxidative capability and mechanism of activated persulfate were investigated.•Thermal and chelated ferrous activated persulfate showed high removal of PAHs.•Thermal activation facilitated high molecular weight PAHs removal by persulfate.•Hydroxyl radicals in thermal activated systems contribute to high PAHs removal. The influence of persulfate activation methods on polycyclic aromatic hydrocarbons (PAHs) degradation was investigated and included thermal, citrate chelated iron, and alkaline, and a hydrogen peroxide (H2O2)-persulfate binary mixture. Thermal activation (60°C) resulted in the highest removal of PAHs (99.1%) and persulfate consumption during thermal activation varied (0.45–1.38g/kg soil). Persulfate consumption (0.91–1.22g/kg soil) and PAHs removal (73.3–82.9%) varied using citrate chelated iron. No significant differences in oxidant consumption and PAH removal was measured in the H2O2–persulfate binary mixture and alkaline activated treatment systems, relative to the unactivated control. Greater removal of high molecular weight PAHs was measured with persulfate activation. Electron spin resonance spectra indicated the presence of hydroxyl radicals in thermally activated systems; weak hydroxyl radical activity in the H2O2–persulfate system; and superoxide radicals were predominant in alkaline activated systems. Differences in oxidative ability of the activated persulfate were related to different radicals generated during activation.