Persulfate Treatment of Dissolved Gasoline Compounds

Bench-scale treatability of an ensemble of gasoline compounds was investigated using unactivated and activated persulfate. The activation strategies explored were chelated-iron, peroxide, alkaline conditions, and the presence of aquifer solids. Batch reactor trials were designed with an initial total petroleum hydrocarbon (TPH) concentration of $\sim 25\mathrm{mg}/\mathrm{L}$, and nine organic compounds were monitored over a 28-day reaction period. First-order oxidation rate coefficients ($k_{\mathrm{obs}}$) were estimated for all experimental trials. Unactivated persulfate at a concentration of $20\mathrm{g}/\mathrm{L}$ resulted in almost complete oxidation of benzene, toluene, ethylbenzene, and xylenes (BTEX) ($>99\%$), trimethylbenzenes ($>95\%$), and significant oxidation of naphthalene ($\sim 70\%$). Oxidation rate coefficients were enhanced by 2–15 times using the peroxide or chelated-iron activation strategy. Alkaline activation at pH 11 or 13 yielded $k_{\mathrm{obs}}$ that were $\sim 2$ times higher than the unactivated case, except for the $k_{\mathrm{obs}}$ for benzene, toluene, and ethylbenzene, which were reduced by 50% at pH 13. Natural activation by two aquifer materials resulted in $k_{\mathrm{obs}}$ similar to the unactivated case. Significant oxidant strength (60–85%) was observed in all $20\mathrm{g}/\mathrm{L}$ persulfate reactors, implying significant persulfate persistence under gasoline-contaminated conditions. The overall bulk gasoline stoichiometry for these experimental trials varied from 120 to 340 g-persulfate/g-TPH.