Groundwater remediation by in-situ membrane ozonation: Removal of aliphatic 1,4-dioxane and monocyclic aromatic hydrocarbons

Groundwater contamination by widespread and persistent organic compounds requires extensive treatment efforts, for example by in-situ chemical oxidation (ISCO). In this study, we investigated ozone mass transfer and removal mechanisms of ozone-resistant monocyclic aromatic and non-aromatic compounds in a novel in-situ treatment method using ozone-permeable membranes as reactive barrier. Initial batch experiments confirmed fast depletion of ozone in presence of sub-stoichiometric benzoic acid (BA), in contrast to the non-aromatic 1,4-dioxane (DIOX), where ozone depleted much slower. Simulated in-situ membrane ozonation treatment of contaminated groundwater led to lower removal of 5 mg L⁻¹ BA (52.7%) compared to DIOX (60.6%). Inhibited removal of BA compared to additional batch experiments could be explained by quick depletion of ozone by reactive intermediates on the membrane surface. Surprisingly, reactive porous media did not lead to substantial changes of in-situ DIOX oxidation, although a stronger impact of the media on DIOX oxidation was hypothesized. Furthermore, experimental ozone mass transfer coefficients were determined (3.94∙10⁻⁷ – 3.12∙10⁻⁶ m s⁻¹) and compared to modeled values for different membrane types (polydimethylsiloxane and polytetrafluoroethylene). Finally, a mathematical model based on mass transfer data was developed to support upscaling efforts. We concluded that contaminant properties are crucial for the feasibility assessment of in-situ ozone membrane treatment technology.