Co-regulation of substrate flux and biomass density for enhanced ammonia assimilation under saline conditions

Drawing inspiration from the self-regulating carbon-nitrogen cycling of saline ecosystems, this study investigates how substrate flux and biomass density co-regulate the structure and function of marine sediment-derived halophilic heterotrophic ammonia assimilation (HAA) microbiome cultivated in saline ammonia-containing wastewater with a COD/N radio of 20 under volumetric exchange ratios (VER) of 75 %, 50 %, and 25 % and mixed liquor suspended solids (MLSS) increasing from 5 to 15 g/L. The combined variation in VER and MLSS generated a gradient in food-to-microorganism radio (F/M). With increasing in biomass, COD removal efficiencies peaked at 94.4-99.3 % at 15 g MLSS/L, whereas ammonia removal efficiencies reached at 90.3-96.8 % at 12.5 g MLSS/L before declining. A VER of 25 % reduced sludge activity, while a VER of 75 % impaired floc settleability. The directed HAA community shifted in substrate flux and biomass density, centering on dominant genera such as Halomonas and Marinobacter, ultimately forming a stable microbiome.