Performance and ammonium migration in a three-chamber microbial desalination cell under high ammonium loading

Treating high-ammonia wastewater remains a significant challenge, primarily due to high energy consumption, risks of secondary pollution, and insufficient operational stability. Microbial Desalination Cells (MDCs), a bioelectrochemical technology, offer potential for simultaneous pollutant removal and energy recovery. However, a systematic understanding of their performance under high ammonia loads (e.g., > 1000 mg/L NH₄-N) and the coupled effects of key operational parameters is lacking. This study constructed a three-chamber MDC to evaluate the effects of inter-electrode spacing, initial desalination-chamber NH₄-N concentration, and anodic substrate type on electrochemical output and apparent NH₄-N migration-related performance under controlled batch conditions. In addition, desalination-chamber NH₄-N concentration profiles were descriptively compared under different anodic COD levels. Results showed that decreases in NH₄-N concentration in the desalination chamber were consistent with transmembrane ion transport under the tested batch conditions, as evaluated using the membrane-area-normalized apparent migration flux ([Formula: see text]). Shortening the inter-electrode spacing from 5.5 to 3.5 cm increased the NH₄-N migration removal rate ([Formula: see text]) from 2.12 to 3.17 mg L^- 1 h^- 1 and [Formula: see text] from 42.4 to 63.4 mg m^- 2 h^- 1. Compared with glucose, acetate increased [Formula: see text] from 55.8 to 77.8 mg m^- 2 h^- 1. These results identify operating-condition-dependent changes in apparent NH₄-N migration-related performance and reveal their trade-off with power output and COD-removal-based coulombic efficiency (CE). The findings provide a laboratory-scale basis for subsequent contribution-partitioning studies and enrichment-side recovery coupling.