Precise control of iron activating persulfate by current generation in an electrochemical membrane reactor

Activated persulfate (PS) oxidation is promising for contaminant removal but a lack of controllable activation can lead to a loss of reagents and thus low contamination degradation. Herein, we have proposed and investigated an innovative method to control PS activation by introducing ion exchange membrane into electrochemically activated PS. This electrochemical membrane reactor (EMR) could precisely control PS activation by adjusting electrical current for slow release of Fe²⁺, and also avoid direct contact between PS and a sacrificial anode electrode (iron electrode)/an alkaline cathode solution. It was found that the PS decomposition rate constant was linearly increased by increasing the applied current (R² = 0.988). The rate of the released Fe²⁺ also exhibited a linear relationship with the applied current (R² = 0.995). Compared to one-time dosage of Fe²⁺, the EMR-based slow-release process had higher contamination degradation and better PS utilization (molar ratio of the decomposed PS to the migrated Fe, 1.04 ± 0.01:1), thereby minimizing the waste of both reaction reagents and generated radicals. The EMR was also employed to degrade a representative dye contaminant in a controllable manner and achieved 95.7 ± 0.7% removal percentage with PS dosage of 3.0 g L^-1 within 20 min. This study is among the earliest to explore effective approaches for precisely controlling PS activation and subsequent oxidation of contaminants.