Peroxydisulfate Persistence in ISCO for Groundwater Remediation: Temperature Dependence, Batch/Column Comparison, and Sulfate Fate.

The persistence of peroxydisulfate anion (S₂O₈²⁻) in soil is a key factor influencing the effectiveness of in situ chemical oxidation (ISCO) treatments, which use S₂O₈²⁻ (S₂O₈²⁻ based ISCO) to remediate contaminated groundwater. However, only a few studies have addressed aspects of S₂O₈²⁻ persistence, such as the effect of temperature and the fate of sulfates (SO₄²⁻) generated by S₂O₈²⁻ decomposition in real soil and/or aquifer materials. Additionally, there are no studies comparing batch and dynamic column tests. To address these knowledge gaps, we conducted batch tests with varying temperatures (30–50 °C) and initial S₂O₈²⁻ concentrations (2.7 g/L and 16.1 g/L) along with dynamic column experiments (40 °C, 16.1 g/L) with comprehensively characterized real soil/aquifer materials. Furthermore, the principal component analysis (PCA) method was employed to investigate correlations between S₂O₈²⁻ decomposition and soil material parameters. We found that S₂O₈²⁻ decomposition followed the pseudo-first-order rate law in all experiments. In all tested soil materials, thermal dependence of S₂O₈²⁻ decomposition followed the Arrhenius law with the activation energies in the interval 65.2–109.1 kJ/mol. Decreasing S₂O₈²⁻ concentration from 16.1 g/L to 2.7 g/L led to a several-fold increase (factor 2–11) in bulk S₂O₈²⁻ decomposition rate coefficients (k′) in individual soil/aquifer materials. Although k′ in the dynamic column tests showed higher values compared to the batch tests (factor 1–3), the normalized S₂O₈²⁻ decomposition rate coefficients to the total BET surface were much lower, indicating the inevitable formation of preferential pathways in the columns. Furthermore, mass balance analysis of S₂O₈²⁻ decomposition and SO₄²⁻ generation suggests the ability of some systems to partially accumulate the produced SO₄²⁻. Principal Component Analysis (PCA) identified total organic carbon (TOC), Ni, Mo, Co, and Mn as key factors influencing the decomposition rate under varying soil conditions. These findings provide valuable insights into how S₂O₈²⁻ behaves in real soil and aquifer materials, which can improve the design and operation of ISCO treatability studies for groundwater remediation. [ABSTRACT FROM AUTHOR]