Recent advances in sub-stoichiometric TiO2 as reactive electrochemical membranes (REM) for bio-refractory pollutants removal: A critical review

Abstract

Water stress must be addressed by developing cost-effective wastewater treatment technologies. Reactive electrochemical membranes (REM) have gained popularity in this scenario due to the benefits of both electrochemical advanced oxidation processes (EAOP) and membrane filtration processes (MFP) in reducing mass transport limitations and fouling issues. In this context, this review aims to consolidate recent advances in REM, focusing on sub-stoichiometric titanium oxide-based REM (TiSO-REM), mainly Ti4O7, the most promising ceramic material due to its high conductivity and ability to generate •OH. The primary fabrication methods for TiSO porous anodes are discussed, resulting in a significant reminder of their electrocatalytic, porosimetric and physicochemical intrinsic properties. In addition to the real advantages of using this material in flow-through configurations, which allow convection-enhanced mass transport and provide a high electrochemical surface area. The latest progresses in TiSO-REM are presented, with specific emphasis on understanding the main operating parameters in performance efficiency: the determinative key role among pollutant nature, matrix effect and anode in removal mechanisms, and where the anode is in relation to the cathode in the reactor design. These points are intended to identify process limitations and challenges to be overcome when implementing various reactor configurations until the scaling-up. All these aspects are reviewed critically in order to provide future research directions for the industrial advancement of this technique, which has proven to be more energy-efficient and therefore economically feasible than alternative EAOP.