“…Indirect processes can be promoted from oxygen or salts contained in the electrolyte that lead to the formation of species such as hydrogen peroxide (Paz et al, 2019;Souza et al, 2019), ozone (García-Morales et al, 2013), peroxosulphates (Balaji et al, 2015;Wacławek et al, 2017;Wang and Wang, 2018) , peroxophosphates and active chlorine species (de Moura et al, 2015). Alternatively, indirect processes can also be promoted with the addition of metal ions such as Ag, Ce, Co, Fe and Mn to acid solutions, used as electrolytes (Govindan et al, 2012a;Govindan and Moon, 2013;Muthuraman and Moon, 2017).In these cases, the process consists of the anodic oxidation of the metal from its stable oxidation state (M Z+) to a higher oxidation state (M Z+1 ), so that later this species reacts with the pollutants, regenerating its reduced state (M Z+ ).…”