Why Electrochemical Oxidation is Efficient in Effluents Treatment?

Why Electrochemical Oxidation is Efficient in Effluents Treatment?

Electrochemical technologies, providing versatility, energy efficiency, amenability to automation, environmental compatibility, and cost efficiency have reached a promising stage of development and can now be effectively used for the destruction of toxic or biorefractory organics of effluents. Advanced oxidation processes have been employed for treating industrial and domestic effluents.

The electrochemical method offers two options for the treatment of these effluents containing pollutants, with the aim of oxidizing them, not only to CO2 and H2O but to biodegradable products by direct and mediated electrochemical oxidation: Electrochemical oxidation (EO), involving or not, heterogeneous species formed from water discharge, follows two approaches: (i) Direct anodic oxidation (or direct electron transfer to the anode). (ii) Chemical reaction with electrogenerated species from water discharge at the anode such as physically adsorbed ‘‘active oxygen’’ (physisorbed hydroxyl radical (•OH)) or chemisorbed ‘‘active oxygen’’ (oxygen in the lattice of a metal oxide (MO) anode).

The action of these oxidizing species leads to total or partial decontamination, respectively. Indirect electro-oxidation (IEO) involving the homogeneous reaction of organic pollutants with strong oxidants generated during electrolysis: (i) The electro-oxidation with active chlorine, where direct anodic oxidation of chloride ion present in the effluent leads to the formation of free chlorine and/or chlorine-oxygen species that can oxidize organic pollutants in the bulk until overall mineralization. (ii) The electro-Fenton process in which organics can be mineralized with homogeneous • OH formed from Fenton’s reaction between added catalytic Fe2+ and H2O2 electrogenerated from O2 reduction at a suitable cathode.

In the case of indirect electrochemical oxidation, pollutants are also competitively destroyed by direct anodic oxidation and by reaction with heterogeneous • OH and other reactive oxygen species (ROS) and weaker oxidants produced from anodic oxidation of water and anions of the electrolyte. The existence of indirect or mediated oxidation with different oxidant species has allowed the proposal of new alternatives for pollution abatement in wastewaters.