In situ iron activated persulfate oxidative fluid sparging treatment of TCE contamination — A proof of concept study

In situ chemical oxidation (ISCO) is considered a reliable technology to treat groundwater contaminated with high concentrations of organic contaminants. An ISCO oxidant, persulfate anion (S2O82−) can be activated by ferrous ion (Fe2+) to generate sulfate radicals (Eo = 2.6 V), which are capable of destroying trichloroethylene (TCE). The property of polarity inhibits S2O82− or sulfate radical (SO4−) from effectively oxidizing separate phase TCE, a dense non-aqueous phase liquid (DNAPL). Thus the oxidation primarily takes place in the aqueous phase where TCE is dissolved. A bench column study was conducted to demonstrate a conceptual remediation method by flushing either S2O82− or Fe2+ through a soil column, where the TCE DNAPL was present, and passing the dissolved mixture through either a Fe2+ or S2O82− fluid sparging curtain. Also, the effect of a solubility enhancing chemical, hydroxypropyl-β-cyclodextrin (HPCD), was tested to evaluate its ability to increase the aqueous TCE concentration. Both flushing arrangements may result in similar TCE degradation efficiencies of 35% to 42% estimated by the ratio of TCE degraded/(TCE degraded + TCE remained in effluent) and degradation byproduct chloride generation rates of 4.9 to 7.6 mg Cl− per soil column pore volume. The addition of HPCD did greatly increase the aqueous TCE concentration. However, the TCE degradation efficiency decreased because the TCE degradation was a lower percentage of the relatively greater amount of dissolved TCE by HPCD. This conceptual treatment may serve as a reference for potential on-site application.