Surfactant-enhanced in-situ oxidation of DNAPL source zone: Experiments and numerical modeling

Zeynep Demiray; Nihat Hakan Akyol; Gokçe Akyol; Nadim K Copty

doi:10.1016/j.jconhyd.2023.104233

Surfactant-enhanced in-situ oxidation of DNAPL source zone: Experiments and numerical modeling

J Contam Hydrol. 2023 Sep:258:104233. doi: 10.1016/j.jconhyd.2023.104233. Epub 2023 Aug 14.

Authors

Zeynep Demiray¹, Nihat Hakan Akyol², Gokçe Akyol³, Nadim K Copty⁴

Affiliations

¹ Institute of Environmental Sciences, Bogazici University, Bebek, 34342 Istanbul, Turkey.
² Department of Geological Engineering, Kocaeli University, 41380 Kocaeli, Turkey.
³ Department of Geological Engineering, Kütahya Dumlupınar University, Kütahya, Turkey.
⁴ Institute of Environmental Sciences, Bogazici University, Bebek, 34342 Istanbul, Turkey. Electronic address: ncopty@boun.edu.tr.

PMID: 37625208
DOI: 10.1016/j.jconhyd.2023.104233

Abstract

In this study we investigate the synergetic effects of combining surfactant-enhanced dissolution with in-situ oxidation of a pool-dominated PCE DNAPL source zone entrapped in porous media. Flow cell flushing experiments packed with silica sand and natural calcareous soil were conducted with a surfactant (Tween 80) and permanganate (MnO₄^-) used as dissolution and oxidation agents, respectively. The resultant breakthrough curves exhibited a multiple step behavior with mass removal controlled in the latter stages by the less-accessible DNAPL mass. DNAPL spatial architecture, flow-field heterogeneity, and flushing solution all influenced the remediation effort. When taking into account both the surfactant-enhanced dissolution and permanganate oxidation processes, mass-flux reduction/mass-removal behavior relationships indicated that the inclusion of oxidation in the remediation scheme delayed the drop in mass flux from the source zone, leading to improved DNAPL removal efficiency. Numerical modeling was also performed to further evaluate the efficacy of the surfactant-enhanced chemical oxidation of DNAPL PCE with permanganate. The system of reaction equations available in the multiphase flow simulator UTCHEM were adapted to simulate the chemical oxidation process in the presence of a surfactant. The model results yield lower oxidation reaction rate constants in the presence of Tween 80, indicating that Tween 80 can interfere with the reaction rate. However, the increase in the solubility of PCE in the presence of Tween 80 more than compensates for the decrease in reaction rate constant. Overall, for Tween 80/MnO₄^- applied at sufficient dosages, more efficient DNAPL zone remediation was achieved compared to surfactant flushing or permanganate oxidation alone.

Keywords: DNAPL; Groundwater remediation; Multiphase flow modeling; Permanganate; Surfactant-enhanced oxidation; Tetrachloroethene.