Selective oxidation of naphthalene-BTEX co-contaminants by permanganate: mechanism and heterogeneity controls.
Source: PubMed, NCBI / U.S. National Library of Medicine
Mixed naphthalene-BTEX contamination is commonly encountered in petroleum-impacted aquifers, where remediation performance is jointly controlled by contaminant reactivity and subsurface heterogeneity. This study investigated the selective oxidation of naphthalene-BTEX mixtures by potassium permanganate (KMnO4) in heterogeneous sandy aquifers through batch tests, sandbox experiments, and three-dimensional reactive transport modelling. Batch experiments were used to determine suitable oxidant conditions, whereas component-specific oxidation behaviour was evaluated using sandbox experiments and numerical simulations. The batch results identified near-neutral conditions (pH 6) and a KMnO4 concentration of 1000 mg/L as appropriate operating parameters for subsequent analyses. Based on these conditions, a three-dimensional coupled transport-reaction model was established and validated against time-series concentration data collected at representative locations in the sandbox system. The results showed that heterogeneous media produced higher oxidant concentration peaks and lower residual naphthalene fractions than homogeneous media, indicating that channelised flow enhanced localised oxidant delivery and oxidant-contaminant contact. Increasing the permeability contrast factor (H) improved oxidant-contaminant overlap along preferential flow paths and increased overall removal efficiency, but it also intensified oxidant bypassing of low-permeability zones. In the mixed system,
Abstract
Mixed naphthalene-BTEX contamination is commonly encountered in petroleum-impacted aquifers, where remediation performance is jointly controlled by contaminant reactivity and subsurface heterogeneity. This study investigated the selective oxidation of naphthalene-BTEX mixtures by potassium permanganate (KMnO4) in heterogeneous sandy aquifers through batch tests, sandbox experiments, and three-dimensional reactive transport modelling. Batch experiments were used to determine suitable oxidant conditions, whereas component-specific oxidation behaviour was evaluated using sandbox experiments and numerical simulations. The batch results identified near-neutral conditions (pH 6) and a KMnO4 concentration of 1000 mg/L as appropriate operating parameters for subsequent analyses. Based on these conditions, a three-dimensional coupled transport-reaction model was established and validated against time-series concentration data collected at representative locations in the sandbox system. The results showed that heterogeneous media produced higher oxidant concentration peaks and lower residual naphthalene fractions than homogeneous media, indicating that channelised flow enhanced localised oxidant delivery and oxidant-contaminant contact. Increasing the permeability contrast factor (H) improved oxidant-contaminant overlap along preferential flow paths and increased overall removal efficiency, but it also intensified oxidant bypassing of low-permeability zones. In the mixed system, naphthalene exhibited the strongest competitive oxidation, followed by ethylbenzene, toluene, and benzene. To quantify this competitive behaviour, a reaction selectivity coefficient (S) was proposed to describe the relative allocation of oxidant consumption among coexisting contaminants. These findings clarify how aquifer heterogeneity regulates oxidant transport and selective oxidation and provide a mechanistic framework for improving ISCO design in heterogeneous aquifer systems.