Removal of Steroid Hormone Micropollutants by an Electrochemical Carbon Nanotube Membrane Flow‐Through Reactor: Role of Concentration and Degradation Mechanisms

The sustainable provision of water is a major global challenge, exacerbated by increasing micropollutant contamination. Developing advanced treatment processes and understanding the fundamental mechanisms responsible for the water purification processes are therefore imperative. The removal of steroid hormone (SH) micropollutants at environmentally realistic concentrations is investigated using a flow‐through electrochemical membrane reactor (EMR) equipped with a carbon nanotube membrane. This EMR is a novel micro design, minimizes typical mass transfer limitations across varying system parameters, and enables an in‐depth study of the limiting factors at extremely low SH concentrations, typical for micropollutants. The integration of high‐performance liquid chromatography with a flow scintillator analyzer and liquid scintillation counting techniques allows elucidation of the complex interplay between adsorption, degradation, and byproduct transformation that takes place in the EMR. A permeate concentration below the detection limit (<2.5 ng L −1 ) is achieved in the reactor, with the heterogeneous electron transfer identified as the main pathway for steroid hormones degradation. The apparent rate of SH removal in the EMR is linear in the concentration range of 50 to 5 × 10 4 ng L −1 . These findings indicate good potential of EMR for SH removal and provide new knowledge for designing and optimizing the EMR process.