Desalination and water purification through the ion drift of salted water flow due to an electric field in a duct is perhaps a feasible membrane-free technology. Here, the unsteady modulation of ion drift is treated by employing the Poison–Nernst–Plank (PNP) equations in the linear regime. Based on the solution of the PNP equations, the closed-form relationships of the charge density, the ion concentration, the electric field distribution and its potential are obtained as a function of position and time. It is found that the duration of the ion drift is of the order of one second or less. Moreover, the credibility of various electrical circuit models is examined and successfully compared with our solution. Then, the closed form of the surface charge density and the potential that are calculated without the linear approximation showed that the compact layer is crucial for the ion confinement near the duct walls. To test this, nonlinear solutions of the PNP equations are obtained, and the limits of accuracy of the linear theory is discussed. Our results indicate that the linear approximation gives accurate results only at the fluid’s bulk but not inside the double layer. Finally, the important issue of electric field diminishing at the fluid’s bulk is discussed, and a potential method to overcome this is proposed.

A water purification method using a static electric field that may drift the dissolved ions of heavy metals is proposed here. The electric field force drifts the positively charged metal ions of continuously flowing contaminated water to one sidewall, where the negative electrode is placed, leaving most of the area of the duct purified. The steady-state ion distributions, as well as the time evolution in the linear regime, are studied analytically and ion concentration distributions for various electric field magnitudes and widths of the duct are reported. The method performs well with a duct width less than 10⁻³ m and an electrode potential of 0.26 V or more. Moreover, a significant reduction of more than 90% in heavy metals concentration is accomplished in less than a second at a low cost.

The recovery of anthocyanins from winery wastewater constitutes an attractive option for both environmental and commercial valorization, as food colorants and nutraceutical ingredients. In this study, the electric field induced ion drift method is proposed as a promising technique for the purification of wastewater solutions as well as for the accumulation of anthocyanins. The cation of the anthocyanidin malvidin (C₁₇H₁₅O₇⁺) was selected as the most representative of winery waste, in order to develop a theoretical model. The main principle of the model is based on the displacement of charged anthocyanin ions, under the influence of an electric field vertical to the flow of the solution, and their accumulation on the side walls of a conductor. Apparatus inducing an electric field drift is described, and critical parameters (i.e., final spatial distribution of concentration, electric field intensity, surface charge density, and potential) were calculated. The proposed model succeeded in reducing anthocyanin concentration by more than 90%, for duct widths smaller than 1 mm in the bulk of the solution, for applied potentials φ(0) in the range of 0.2–0.4 V and target concentrations equal to 1.2 × 10⁻³ mol/m³.

Bacterial protein toxins secreted by foodborne pathogens, such as Staphylococcus aureus and Shiga toxin-producing Escherichia coli (STEC) strains, may cause severe toxicosis in humans if present in foods or water and constitute an important public health problem. These toxins are large biomolecules with negative and positive ions due to the ionizable groups in the residual amino acids. An innovative theoretical model of purifying aqueous flowing solutions from ionic toxins is proposed in this study. The principle of the model is based on the drift of the ionic toxins, under the application of the external electric field, towards the walls of the duct, leaving the largest part of the duct with reduced levels of toxin. Parameters, such as toxin concentration, potential and electric field intensity distributions, and surface charge densities, are studied analytically for various duct widths and various external electric fields. The proposed model succeeded to reduce toxin levels by more than 99%, for duct widths less than 1cm, making it suitable for small-scale water purification.

Water scarcity stands as a critical challenge of our era, affecting approximately four billion individuals who confront severe water shortages for at least one month annually