Electrochemical Remediation of Marine Sediments under very Low Electric Fields

To date, remediation, protection, and restoration of contaminated sites is a global concern. Current technologies to restore soil/sediments characterized by heterogeneous characteristics, several pollutants, fine grains, and low hydraulic permeability are poorly effective; hence their remediation is still challenging [1]. Among the investigated approaches for the remediation of such complex sites, Direct Current Technologies (DCTs), whereby an electric field (E) is induced through the polluted media thanks to the application of a direct current between two or more electrodes directly inserted or adjacent to the contaminated site, are considered among the most practical, sustainable, cost-effective and noninvasive in situ and ex situ options. In these treatments, the induced E promotes i) electromigration, electroosmosis, electrophoresis of ions, water, colloids and contaminants and ii) redox reactions at the electrodes and/or on the soils’ particles, prompting the remediation of the contaminated site [2-4]. ElectroChemical Remediation Technologies (ECRTs) and ElectroKinetics (EKs) are two types of DCTs used for environmental remediation, which mainly differ in energy input intensity, operative mechanisms and resulting outcomes. ECRTs consist of two main processes: i) ElectroChemical GeoOxidation (ECGO), which mineralizes organics, and ii) induced complexation, which complexes metal contaminants. ECGO technologies involve less energy (i.e., typical 0.0025 ≤ E ≤ 0.25 V cm− 1) than the EK processes (i.e., E ≥ 1 V cm− 1) without using costly processing fluids [2]. In this framework, this work aims to present the results achieved for the electrochemical treatment under very low electric fields (≤0.25 V cm− 1) of both i) clays polluted by phenol [2] or a mixture of five petroleum hydrocarbons [3] and ii) marine sediments (dragged from Capo Granitola Coast (Trapani), clayed Augusta Bay (Syracuse) and sandy Bagnoli-Coroglio Bay (Naples) in Italy) contaminated by PAHs and heavy metals [3]. The common finding is that, regardless of the nature of organics (i.e. phenol, alkanes, PAHs) and treated soil/sediments (kaolin, clay sand), the usage of very low E values applied by inserting the electrodes directly into the sediments and without the usage expensive processing fluids can allow to simultaneously desorb, transport and also degrade in situ the organic contaminants. As an example, in the cases of real marine sediments from Augusta Bay and Bagnoli Bay, total PAHs removal efficiencies higher than 50% were reached after 96 h of treatment under 0.05 V cm−1 coupled with a low energetic consumption due to the rather E values adopted. In addition, it was observed that, under the adopted conditions the used approach is unsuitable for the remediation of heavy metals (i.e. Hg and As). [1] K.R. Reddy, C. Cameselle, Electro-chemical remediation technologies for polluted soils. sediments and groundwater, John Wiley & Sons,, Hoboken, New Jersey, 2009. [2] F. Proietto, A. Khalil, W. Maouch, A. Galia, O. Scialdone, Environmental Technology & Innovation 32 (2023) 103286. https://doi.org/10.1016/j.eti.2023.103286. [3] F. Proietto, P. Meli, C. Prestigiacomo, A. Galia, O. Scialdone, , Journal of Environmental Chemical Engineering 12 (2024) 111780. https://doi.org/10.1016/j.jece.2023.111780. [4] F. Proietto, F. D’Agostino, M. Bonsignore, M. Del Core, M. Sprovieri, A. Galia, O. Scialdone, Chemosphere 350 (2024) 141009. https://doi.org/10.1016/j.chemosphere.2023.141009.