Benzene oxidation by Fe(III)-activated percarbonate: matrix-constituent effects and degradation pathways

Complete degradation of benzene by the Fe(III)-activated sodium percarbonate (SPC) system is demonstrated. Removal of benzene at 1.0 mM was seen within 160 min, depending on the molar ratios of SPC to Fe(III). A mechanism of benzene degradation was elaborated by free-radical probe-compound tests, free-radical scavengers tests, electron paramagnetic resonance (EPR) analysis, and determination of Fe(II) and H₂O₂ concentrations. The degradation products were also identified using gas chromatography-mass spectrometry method. The hydroxyl radical (HO^[rad]) was the leading species in charge of benzene degradation. The formation of HO^[rad] was strongly dependent on the generation of the organic compound radical (R^[rad]) and superoxide anion radical (O₂^[rad]−). Benzene degradation products included hydroxylated derivatives of benzene (phenol, hydroquinone, benzoquinone, and catechol) and aliphatic acids (oxalic and fumaric acids). The proposed degradation pathways are consistent with radical formation and identified products. The investigation of selected matrix constituents showed that the Cl⁻ and HCO₃⁻ had inhibitory effects on benzene degradation. Natural organic matter (NOM) had accelerating influence in degrading benzene. The developed system was tested with groundwater samples and it was found that the Fe(III)-activated SPC has a great potential in effective remediation of benzene-contaminated groundwater while more further studies should be done for its practical application in the future because of the complex subsurface environment.