Single and Coupled Electrochemical Processes and Reactors for the Abatement of Organic Water Pollutants: A Critical Review

Abstract

Traditional physicochemical and biological techniques, as well as advanced oxidation processes (AOPs), are often inadequate, ineffective, or expensive for industrial water reclamation. Within this context, the electrochemical technologies have found a niche where they can become dominant in the near future, especially for the abatement of biorefractory substances. In this critical review, some of the most promising electrochemical tools for the treatment of wastewater contaminated by organic pollutants are discussed in detail with the following goals: (1) to present the fundamental aspects of the selected processes; (2) to discuss the effect of both the main operating parameters and the reactor design on their performance; (3) to critically evaluate their advantages and disadvantages; and (4) to forecast the prospect of their utilization on an applicable scale by identifying the key points to be further investigated. The review is focused on the direct electrochemical oxidation, the indirect electrochemical oxidation mediated by electrogenerated active chlorine, and the coupling between anodic and cathodic processes. The last part of the review is devoted to the critical assessment of the reactors that can be used to put these technologies into practice.

Electrochemical Advanced Oxidation Processes (EAOP) to degrade per- and polyfluoroalkyl substances (PFASs)

“…[20,24,29] Consequently, EAOP has drawn increasing attention, which can be evidenced by the number of publications shown in Figure 1, and witnessed by recently published reviews [20,23,24,26,[30][31][32][33][34].…”

“…However, this process is slow and depends strongly on the electrocatalytic activity of the electrode, which hampers its application for remediation. Consequently, this aspect will not be discussed further here [31].…”

“…The cell design usually requires two electrodes in parallel with an inter-distance of <1 cm, as presented in Figure 3(a) [48]. The cell can consist of an electrode array, as shown in Figure 3(b), which features an improved degradation efficiency [31]. On the other hand, the cathode can be replaced with cheap materials (c, d), such as a carbon electrode (graphite), even metal ones (cast iron, stainless steel, copper) or air-diffusion electrodes to boost the production of H 2 O 2 [30,41].…”

“…To improve the electrode's shelf life, the anode materials can be modified, such as by doping and nanofabricating [31,32,36,45]. For example, PbO 2 doped with F -was found to inhibit O 2 emission, accelerate oxidation and enhance degradation efficiency [32].…”

“…Further attention should also be paid to the cathode and the reactions occurring there [31]. As a compulsory component of an electrochemical cell, the cathode reaction should be designed to maximise its benefit towards the degradation process.…”