Active chlorine mediated ammonia oxidation in an electrified SnO2-Sb filter: Reactivity, mechanisms and response to matrix effects

Ammonia pollution control has gained increasing attention as a result of the existential threat to the environ-ment. The electrochemical advanced oxidation process has demonstrated to be an attractive and environmentally benign platform for aqueous ammonia removal because it only requires electricity and water as a clean "re-agent". Herein, we developed a porous SnO2-Sb filter toward high-efficient ammonia conversion. Despite the introduction of enhanced convection, chlorine-mediated ammonia oxidation dominated the reaction mechanism of the electrified SnO2-Sb filter at circumneutral pH. At an extremely short hydraulic contact time (1.0-5.1 min), ammonia was primarily oxidized to N2 with no chloramines detected. Matrix effect assays showed that the chloride-to-ammonia ratio was vital to determine the removal rate and product selectivity. A pH buffer, HCO3-, might prompt ammonia removal whilst inhibiting chlorate formation. In contrast, the ammonia removal per-formance of the SnO2-Sb filter deteriorated in the presence of dissolved organic matter (e.g., humic acid). The matrix effects significantly influenced the process efficiency to treat municipal sewage and lake water. The re-sults of this study can advance our understanding of electrochemical ammonia oxidation and provide insight into the effective implementation and optimization of the flow-through process.