Integration of sub-stoichiometric titanium oxide reactive electrochemical membrane as anode in the electro-Fenton process

Abstract Sub-stoichiometric titanium oxide (TiOx) reactive electrochemical membrane (REM) were integrated for the first time as anode in the electro-Fenton (EF) process. Hydroxyl radicals (·OH) were produced both in the retentate from Fenton’s reaction and at the REM from anodic oxidation (AO). Optimal mass transport conditions were implemented because of convection-enhanced mass transport of (i) organic pollutants towards the REM surface during filtration and (ii) dissolved O2 towards cathode active sites owing to the use of a 3D carbon felt cathode in flow-through configuration for H2O2 generation. The efficiency of the REM/EF process was much higher than EF or REM used as standalone processes. For instance, taking paracetamol as target pollutant, (67 ± 2)% removal of 55 mg L-1 of initial TOC was achieved with a high mineralization current efficiency (MCE) of (43 ± 1)%. By comparison, standalone REM and EF processes achieved only 47% (MCE = 30%) and 31% (MCE = 20%) of TOC removal, respectively. By monitoring TOC removal both in retentate and permeate, the effect of homogeneous oxidation in the bulk retentate and heterogeneous oxidation at the REM could be observed separately. It was thus highlighted that the efficiency of AO might be affected by the presence of ·OH and Fe2+ in the bulk. It was also emphasized a synergistic effect related to the formation of carboxylic acids in the bulk retentate that are more easily mineralized at the REM where both ·OH-mediated oxidation and direct electron transfer occur.