Reactive electrochemical ceramic membrane for effective removal of high concentration humic acid: Insights of different performance and mechanisms

Abstract

Refractory organic matter in different water matrices poses tremendous challenges for treatment processes. The substoichiometric titanium oxide (Ti4O7) anode-designed reactive electrochemical membrane (REM) introduced for this critical problem and its performance was comprehensively evaluated in terms of current density, conductivity, membrane flux, total organic carbon (TOC) concentration, and pH using humic acid (HA) as a surrogate refractory organic compound. Increase in membrane flux from 500 to 2000 LMH showed a positive impact on the HA removal. The increase in current density and conductivity improved the mineralization performance. Depending on pH, the induction of electrical current to REM improved the HA removal from 0% to 80% compared to the case without power. It appeared that HA removal was achieved through direct electron transfer, oxidation by hydroxyl radicals (•OH), and electrosorption. The distribution of the three leading phenomena showed electrosorption as the main contributor to HA removal. The noticeable generation of •OH was recorded using electron paramagnetic resonance (EPR), and the structural transformation of HA was confirmed through the blue shift in the major fluorescence peak of HA. The energy consumption per g TOC was recorded to be economical for operation at lab-scale applications and thus highly promising for full-scale consideration. This study showed that REM could remove HA at a medium-level to a higher concentration with extraordinary stability.