Exploring a novel phase-transfer-catalysis synergized with self-activation induced cascade dual-oxidation for enhanced remediation of multi-NAPL-contaminated groundwater.

The remediation efficiency of multi-non aqueous phase liquid (NAPL)-contaminated groundwater was significantly impaired by discrepant oxidation susceptibility among NAPLs and heterogeneous mass transfer limitation. In this study, a novel phase-transfer-catalysis (PTC) synergized with self-activation induced cascade dual-oxidation (PTC-CDO) strategy was proposed, in which representative oxidants permanganate and peroxymonosulfate (PMS) were sequentially applied to establish CDO system. Breakthrough and remediation experiments were conducted in aquifer-simulating sand columns to reveal mechanisms of reagent migration and enhanced remediation. Results indicated that while separate PTC migration lagged behind oxidants, its co-injection with permanganate enabled synchronous migration, thereby promoting phase transfer efficiency of oxidants for efficient NAPL degradation. PTC-CDO achieved trichloroethene and benzene degradation efficiencies of 68.2 % and 78.7 %, respectively, showing 40.0 % and 26.7 % promotions compared to the PTC-free system, with a simultaneous 48.5 % reduction in oxidant dosages required for degrading per gram of NAPLs. Mechanism analysis demonstrated that retained PTC in the first oxidation phase was further utilized in cascaded PMS oxidation phase, promoting dissolved manganese and colloidal MnO2 generation/stabilization, which facilitated PMS activation in the second oxidation phase for remediation enhancement. This study manifested promising potential of PTC-CDO strategy for efficient remediation of groundwater contaminated by multi-NAPLs with significant discrepancy in oxidation susceptibility.