Wastewater treatments by advanced oxidation processes – Anodic oxidation

Advanced electro-oxidation belongs to the family of so-called "advanced" oxidation processes, via the generation of powerful oxidants initiated directly or indirectly by electrochemical oxidation.

Given the relatively high cost of electrochemical processes, they were initially developed for the manufacture of high value-added products. On an industrial scale, the first applications of electro-oxidation were the production of chlorine-soda and the synthesis of organic products.

The scarcity of water resources and the tightening of wastewater discharge standards call for appropriate treatment methods. Biological treatments can eliminate some pollutants (biodegradable fraction), but advanced oxidation processes are required to treat complex effluents containing toxic or poorly biodegradable molecules (refractory fraction). Among these processes, advanced electro-oxidation has the advantage of consuming only electrons, rather than costly or unstable chemical reagents. As a result, it can become competitive in disinfection and organic load treatment, particularly when pollutant concentrations are high, treated flow rates are low and medium salinity is sufficient. Treatment can be carried out in its entirety until mineralization of the refractory and/or toxic organic load, or only partially as a pre-treatment to increase the biodegradability of the molecules prior to biological treatment.

This article presents the advanced anodic oxidation process applied to water treatment, covering the theoretical principle with the types of materials used associated with the different oxidants formed, and the competition between charge transfer and mass transport which is responsible for the oxidation kinetics of the compounds. Implementation is then presented, with details of the methodology to be followed from laboratory to industrial scale, including the necessary equipment, safety aspects and costs involved. Finally, the different types of applications are mentioned, along with examples of elimination efficiencies.