Potential for activated persulfate degradation of BTEX contamination

The present study focused on evaluation of activated persulfate (PS) anion (S2O82−) oxidative degradation of benzene, toluene, ethylbenzene, and xylene (constituents of gasoline and known collectively as BTEX) contamination. The results indicated that BTEX were effectively oxidized by PS in aqueous and soil slurry systems at 20 °C. PS can be activated thermally, or chemically activated with Fe2+ to form the sulfate radical (SO4−) with a redox potential of 2.4 V. The degradation rate constants of BTEX were found to increase with increased persulfate concentrations. For two PS/BTEX molar ratios of 20/1 and 100/1 experiments, the observed aqueous phase BTEX degradation half-lives ranged from 3.0 to 23.1 days and 1.5 to 20.3 days in aqueous and soil slurry systems, respectively. In the interest of accelerating contaminant degradation, Fe2+ and chelated Fe2+ activated persulfate oxidations were investigated. For all iron activation experiments, BTEX and persulfate degradations appear to occur almost instantaneously and result in partial BTEX removals. It is speculated that the incomplete degradation reaction may be due to the cannibalization of SO4− in the presence of excess Fe2+. Furthermore, the effects of various chelating agents including, hydroxylpropyl-β-cyclodextrin (HPCD), ethylenediaminetetraacetic acid (EDTA), and citric acid (CA) on maintaining available Fe2+ and activating PS for the degradation of benzene were studied. The results indicated that HPCD and EDTA may be less susceptible to chelated Fe2+. In contrast, CA is a more suitable chelating agent in the iron activated persulfate system and with a PS/CA/Fe2+/B molar ratio of 20/5/5/1 benzene can be completely degraded within a 70-min period.