Towards an electrochemically-based circular economy: Electro-refinery for valorizing phenolic wastewater

Abstract

This study introduces an innovative approach to wastewater treatment that combines two electrochemical technologies: electrolysis and electrochemical separation facilitated by anionic exchange membranes. This integrated technology converts pollutants into carboxylates, which are valuable intermediates for further electrosynthesis and fuel production. The efficacy of this approach was demonstrated using synthetic wastewater containing phenol as a model pollutant, chosen for its well-documented characteristics that enable comparative analysis with previous studies. The treatment process utilized mixed metal oxides (MMO) anodes with a composition of Ti/(RuO2)0.8(Sb2O4)0.2 and a boron-doped diamond (BDD) anode. The investigation was structured to evaluate each component of the treatment system individually before examining their collective performance. Through a series of case studies, the research not only confirmed the feasibility of this innovative technology but also highlighted the need for further study on the optimization of operational parameters and electrode materials. Comparative analysis revealed that MMO anodes outperformed BDD anodes, achieving maximum carboxylate transport rates of 138.7 mmol m−2h−1. The efficiency of carboxylate separation from the solution where they were generated reached up to 54.6 mmol kWh−1, while the maximum overall production efficiency was 8.77 mmol kWh−1. The study further determined that current density significantly affects both the production rate and the extent of mineralization, identifying optimal densities of 100 mA cm−2 and 30 mA cm−2 for the electrolyzer and electroseparator units, respectively. This work provides valuable insights for the optimization of this promising wastewater treatment technology, with potential applications in various industries.