Mechanisms of Enhanced In-situ Chemical Oxidation for Groundwater Remediation via Ultrasonic Permeability Improvement

Groundwater contamination has become an increasingly critical environmental concern worldwide. In-situ chemical oxidation (ISCO) is considered a promising technology for groundwater remediation, but its performance in heterogeneous aquifers is often constrained by mass-transfer limitations in low-permeability zones, leading to suboptimal treatment efficiency. Theoretically, ultrasound can enhance permeability in low-permeability regions, accelerate oxidant transport, and activate oxidants to strengthen their degradation capacity; however, the remediation performance and underlying mechanisms of ultrasound-ISCO coupling have not yet been systematically validated through experiments. To address this gap, this study conducted degradation experiments under three ultrasonic modes (no ultrasound, ultrasonic pre-treatment, and continuous ultrasound) and employed nuclear magnetic resonance (NMR) to quantitatively characterize contaminant distribution and degradation behavior within the pore space. The results show that ultrasonic pre-treatment reconstructs the pore structure of the porous medium via cavitation and mechanical vibration, thereby enhancing permeability and oxidant mass transfer and consequently accelerating contaminant removal. When ultrasound is continuously applied during ISCO, it not only maintains permeability enhancement but also activates the oxidant, modulates the transformation pathways of key intermediates, and promotes deeper oxidation and mineralization, ultimately yielding the highest degradation efficiency due to the synergistic action of permeability enhancement and oxidant activation. This study demonstrates the effectiveness of ultrasound-ISCO coupled technology for remediation of contaminated heterogeneous aquifers and systematically elucidates the synergistic mechanisms between ultrasonic permeability enhancement and intensified oxidation, providing theoretical support for its engineering application under complex hydrogeological conditions.