Hydrogen peroxide (H2O2) is widely used as an oxidant in the process of in situ chemical oxidation (ISCO) for remediating groundwater contaminated by dense non-aqueous phase liquids (DNAPLs). However, the remediation efficiency is often limited by excessive gas generation and H2O2 self-decomposition. A pore-scale understanding of the dynamic interactions among DNAPL, H2O2, and gas evolution during the ISCO is essential to optimize field-scale treatment applications. This study experimentally investigated the remediation process of residual trichloroethylene (TCE) in porous media using H2O2 as the oxidant. The pore-scale dynamics of the remediation were visualized through time-resolved three-dimensional micro-computed tomography (3D micro-CT). Results demonstrate that the TCE remediation involves a competition between TCE oxidation and H2O2 self-decomposition. At low H2O2 concentrations (<2.0 wt%), remediation improves with increasing H2O2 concentration. However, beyond the critical concentration (2.0 wt%), self-decomposition dominated, consuming H2O2 without degrading TCE. Additionally, gas generation induces pore blockage, restricting oxidant transport to the TCE phase. This study provides pore-scale insights into the mechanisms of H2O2-based TCE remediation, highlighting the multiphase interactions. It reveals the dual role of H2O2 as both an effective oxidant and a source of inefficiency in TCE remediation, leading to H2O2 consumption shift from diffusion-limited TCE degradation to H2O2 self-decomposition.
Wang et al. (Thu,) studied this question.