Revealing Dissolved Organic Nitrogen Transformation and Microbial Evolution at Microscale in a Solid Carbon Source-Coordinated Simultaneous Partial Nitrification, Anammox, and Denitrification Bioreactor

Denitrification coupled with anammox is an effective approach to improve total nitrogen removal from wastewater, especially by reducing the nitrate produced by anammox. Nevertheless, the behavior of dissolved organic nitrogen (DON) is commonly ignored in this process. In the present study, poly(butylene succinate) (PBS), an alternative solid carbon source, was coupled with simultaneous partial nitrification, anammox, and denitrification (SNAD) to achieve complete nitrogen removal in a single reactor. After 90 days of continuous operation, dissolved inorganic nitrogen (DIN) removal efficiencies were 80.7 +/- 1.0% without PBS and 97.4 +/- 3.5% with PBS. Correspondingly, the effluent DON was reduced from 1.0 to 0.6 mg/L when PBS was provided. Fourier transform ion cyclotron resonance mass spectrometry revealed that DON molecules with large, unsaturated and aromatic structures were preferentially transformed in SNAD when PBS was provided. Microbial analysis indicated that Candidatus_Jettenia (22.0%-17.7%) and Nitrosomonas (3.8%- 2.6%) were the predominant functional bacteria for anammox and nitrification, regardless of whether PBS was provided or not. Meanwhile, increased abundances of denitrifying bacteria, such as Denitratisoma (2.9%-4.0%) and Thauera (2.2%-3.3%), were observed and assumed to improve nitrate reduction. The results provide a practical alternative for nitrogen removal by coupling solid denitrification with anammox, and also reveals novel insights about DON characteristics at the molecular level.