Osmotic dewatering accelerates inherent sluggish kinetics of electro-Fenton process: Toward sustainable removal of organic contaminants

Abstract

Refractory organic pollutants, especially at low concentrations, are very slowly degradable through a heterogeneous electro-Fenton (EF) process. This drawback, caused by limited mass transfer between in-situ produced oxidizing agents and organic molecules, negatively affects the overall performance of EF and thus restricts its large-scale deployment. In this study, we provided an innovative solution by integrating the EF process with an osmotically driven membrane technology to overcome this challenge. Osmotic dewatering was conducted to extract water continuously from the EF cell and keep the kinetics of oxidation reaction in its fast state. The hybrid process was operated in two different modes, EF – Forward osmosis (FO) and EF – pressure retarded osmosis (PRO), where the membrane active layer and underlying support faced the feed solution, respectively. Rhodamine B (RhB) and Reactive Red 120 (RR120) were utilized as probe organic contaminants and their degradation rate, total organic carbon (TOC) decay, mineralization current efficiency (MCE), and specific energy consumption (SEC) were evaluated for a single EF and hybrid EF-FO and EF-PRO processes. Comparing with a single EF reaction, TOC decay improved by 57.9 ± 2% and 70.4 ± 6% using EF-FO and EF-PRO processes, respectively. Overall, MCE of hybrid processes surpassed 100% while it remained under 50% for a single EF reaction. SEC calculations showed a significant reduction in energy consumption, by almost one-third, when the EF reaction is integrated with the FO process. To demonstrate the practicality of our hybrid process at a very low concentration of organic pollutants, RhB-containing solution with an initial concentration of 2 ppm was subjected to EF and EF-PRO processes. EF-PRO system demonstrated 88.1% TOC removal which was 3-fold higher than that of a single EF process.