Chlorine-Mediated Ammonia and Organics Transformation during Electrochemical Ammonia Recovery from Human Urine

Electrochemical technology offers efficient ammonia recovery from waste streams. While human urine is a nitrogen-rich resource, its complexity presents challenges, including chlorine-mediated ammonia oxidation and disinfection byproduct formation in the electrochemical process. In this study, we investigate these important issues in a stacked electrochemical system. In situ electrochemical Raman spectroscopy, Fourier Transform ion cyclotron resonance mass spectrometry, and stopped-flow techniques were used to examine chlorine evolution and dissolved organic matter (DOM) transformation. Results showed minor ammonia loss due to chlorination because the Cl₂-to-nitrogen ratio was significantly lower than the breakpoint ratio under anodic conditions (pH < 1.5). However, the generated active chlorine induced hydrogen abstraction and chlorine addition to unsaturated bonds, forming chlorinated DOM in the ammonia-receiving solution. This necessitated activated carbon post-treatment to ensure product quality. The electrochemical system demonstrated stable performance over 390 h with an ammonia removal rate of 24.4 g-N m^-2 h^-1 and consistent removal/recovery efficiencies of 80%. Further attention should be given to control of cathode scaling, anion exchange membrane fouling, and gas permeable membrane wetting. Overall, this study is anticipated to enhance the applicability of electrochemical ammonia recovery technologies.