Substrate-starved aeration drives convergent metabolic reprogramming for dissolved organic nitrogen removal

Dissolved organic nitrogen (DON) has become the dominant residual nitrogen form in effluents from advanced wastewater treatment systems, yet remains poorly controlled, posing an overlooked risk to downstream eutrophication. Here, we demonstrate that DON can be removed by steering microbial metabolic states rather than altering community composition. Substrate-starved aeration emerged as a critical control point, where aerobic conditions under simultaneous labile carbon and ammonium depletion shifted microbial systems from net DON production to consumption through convergent metabolic reprogramming. A 2 h substrate-starved aeration phase could suppress endogenous DON production by >80% and remove >60% of exogenous DON from municipal wastewater effluent without chemical addition, bioaugmentation, or prolonged acclimation. FT-ICR-MS further showed preferential elimination of bioavailable protein- and lipid-like DON fractions. Algal bioassays using Selenastrum capricornutum confirmed that DON removal reduced algal growth potential by 18-48%, highlighting the direct ecological relevance of this process. Together, these findings establish metabolic-state manipulation as a practical and scalable strategy for advanced DON control and highlight bioavailable DON as a critical but overlooked target in wastewater management.