Electrochemical Treatment of Water as an Effective and Emerging Technology

Introduction

Electrochemical treatment processes are used in the treatment of wastewater through the application of direct or alternating current in the electrolyte-containing cell containing the electrodes. Noyes (1993) reported that electrodialysis, electrocoagulation, electro-precipitation, and electrochemical treatment processes are among the major applications of electrical treatment. Electrodialysis is an electrical treatment process in which charged membranes are used to separate ions from aqueous solutions under the driving force of the electrical potential difference. The process utilizes an electrodialysis stack, built on the filter-press principle and containing several hundred individual cells formed by a pair of anion and cation exchange membranes. The cells are arranged in an alternating pattern between an anode and a cathode to form individual cells. The basic principle of the process is that the solution is pumped through these cells and an electrical potential is established between anode and cathode. The cations (positively charged ions) migrate toward the cathode and the anions (negatively charged ions) migrate likewise to anode. The cations pass easily through the negatively charged cation-exchange membrane but are retained by the positively charged anion-exchange membrane (Oke et al., 2012a, b, c, 2017 and 2020).

Similarly, the positively charged anions pass through the anion-exchange membrane and are retained by the cation-exchange membrane. The overall results are ion concentrations increase in the alternate compartments, while the other compartments simultaneously become depleted of ions. The ion-exchange membrane used in the system mainly determines the efficiency of electrodialysis as a separation process. The operational costs are dominated by the energy consumption and investment costs for the plant of the desired capacity. The energy required in an electrodialysis process is an additive of two terms: the electrical energy to transfer the ionic components from solution through the membranes into another solution and the energy required to pump the solutions through the electrodialysis unit. These costs are a function of the membrane used in the process. It varies with various design parameters used. The major design parameters for the process are cell dimensions, feed flow velocity, and the pressure drop of the feed solution in the cell (Noyes, 1993). The capital cost of an electrodialysis plant is proportional to the membrane area required for a certain plant capacity, which is determined mainly by the feed solution concentration and the limiting current density. It has its principal application in the desalting of brackish wastewater. There are no fundamental limits of electrodialysis other than the limit to solution separation with a specified maximum concentration level. In addition, Grebenyuk et al. (1998) listed some of the usefulness of electrodialysis in the industrial world nowadays (Oke et al., 2012a, b, c, 2017 and 2020).