Regulatory effects of influent carbon/nitrogen ratios on microbial desalination cell performance: Insights into...

The regulatory role of carbon/nitrogen (C/N) ratios in microbial desalination cells (MDCs) treating ammonium-rich wastewater was investigated, focused on the interplay with salinity gradients and electron transfer. Through integrated analysis of electrochemical behavior, nitrogen pathways, and microbial succession under varying C/N ratios (18, 9, and 6), optimal performance was achieved at a C/N ratio of 9, demonstrating high removal efficiencies for carbon (93.4 %), nitrogen (86.5 %), and salt (90.7 %), alongside peak power density of 586 mW/m². This enhancement was attributed to improved biofilm viability, lower charge transfer resistance, and protein-enriched extracellular polymeric substances that facilitated efficient electron shuttling. Conversely, lower C/N ratio induced ammonium toxicity, significantly increasing resistance and suppressing electroactive bacteria. The enriched genera (Vitreoscilla, Brevefilum, and Smithella) and key functional pathways (nitrification, denitrification, and anammox) synergistically drove bioelectricity enhancement and nitrogen transformation. This work establishes C/N stoichiometry as a master regulator of the electro-microbiological nexus in hypersaline wastewater treatment.