Impact of catalyst, chelating agent and light irradiation on electro-Fenton performance under not optimal conditions

Electro-Fenton is a promising game-changer for distributed wastewater treatments for the removal of recalcitrant compounds that it is possible to find in industrial effluent and looking for a water reuse approach. This electrochemical advanced oxidation process (EAOPs) is able to provide fast removal of organic compounds, like dyes, due to the in-situ H₂O₂ production and its reaction with Fe²⁺ to form hydroxyl radicals. The literature clearly reports that this reaction reaches its optimum in acid conditions (pH = 3) and low catalyst concentrations [Fe²⁺<0.5 mM]. This paper wants to investigate the effects of the shifting from optimal conditions on the removal of reactive black 5 (RB5), treating solutions which contain a higher amount of catalyst and a less acid pH. Textile effluents usually contain also other metals able to act as catalyst for Fenton reaction, like copper. Here its activity has been investigated as well as the possible synergistic effect with Fe²⁺. The results confirm that copper can enhance RB5 removal, especially in those conditions critical for ferrous cation. In the second part, possible process modifications to overcome the issues introduced by unfavourable operating conditions (pH > 3 and Fe²⁺ > 0.5 mM) are considered, such as the usage of a chelating agent (EDTA) and the application of a light source. The results show the positive impact of these two system modifications highlighting the possibility to enlarge the application window of electro-Fenton systems.