Challenges and Opportunities for Electrochemical Processes as Next-Generation Technologies for the Treatment of Contaminated Water

Abstract

Electrochemical processes have been extensively investigated for the removal of a range of organic and inorganic contaminants. The great majority of these studies were conducted using nitrate-, perchlorate-, sulfate-, and chloride-based electrolyte solutions. In actual treatment applications, organic and inorganic constituents may have substantial effects on the performance of electrochemical treatment. In particular, the outcome of electrochemical oxidation will depend on the concentration of chloride and bromide. Formation of chlorate, perchlorate, chlorinated, and brominated organics may compromise the quality of the treated effluent. A critical review of recent research identifies future opportunities and research needed to overcome major challenges that currently limit the application of electrochemical water treatment systems for industrial and municipal water and wastewater treatment. Given the increasing interest in decentralized wastewater treatment, applications of electrolytic systems for treatment of domestic wastewater, greywater, and source-separated urine are also included. To support future adoption of electrochemical treatment, new approaches are needed to minimize the formation of toxic byproducts and the loss of efficiency caused by mass transfer limitations and undesired side reactions. Prior to realizing these improvements, recognition of the situations where these limitations pose potential health risks is a necessary step in the design and operation of electrochemical treatment systems.

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].…”

“…For example, the presence of Cl -can generate Cl 2 , HClO, HClO 2 , HClO 3 , HClO 4 [35] and the corresponding radicals [40], SO 4 2− can generate S 2 O 8 2− and radicals as well [34]. In some cases, the EAOP can be enhanced, such as S 2 O 8 2− as a strong oxidant and Fe 2+/3+ as a media that activates Fenton reaction [41].…”

“…In other cases, some by-products might bring about the secondary contamination, such as ClO 4 − (an EC itself). Hence, those parameters should be considered and optimised for subsequent improvement and development [34,36].…”

“…As stated previously, to boost the productivity of radicals and inhibit the emission of O 2 , the electrode materials reported in literatures include platinum (Pt) [43], carbon or graphite (C) [44,45], iridium dioxide (IrO 2 ) [46], ruthenium dioxide (RuO 2 ) [47], tin dioxide (SnO 2 ) [48], boron-doped diamond (BDD) [49], lead dioxide (PbO 2 ) [32], Ti 4 O 7 (Ebonex) [39], TiO 2 nanotube array [34] as well [24,36]. Among them, BDD has been reported to be the best for water treatment [49].…”

“…The configuration might also behave as a flow-through cell (cylinder or porous panels) (d, e) to increase the transportation efficiency [33,36]. In Figure 3(d, e), in order to enhance the degradation efficiency, the space between the anode and cathode can be filled with nanomaterials (such as functionalised activated carbon) or an additional electrode couple [34,51]. …”