Molecular characterization of dissolved organic nitrogen during anoxic/oxic and anammox processes using ESI FT–ICR MS

Abstract

Dissolved organic nitrogen (DON) is a component of wastewater with a negative influence on the environment. The removal of DON is conducted through the anoxic/oxic (A/O) and anammox processes. However, the mechanisms and chemical preferences in the removal of DON compounds have not been understood and compared so far. This study, for the first time, comparatively investigated the molecular‐level characteristics of DON during both processes by using FT–ICR MS (Fourier transform ion cyclotron resonance mass spectrometry). The results indicated that the number of DON formulas increased from 1844 to 1935 during A/O process, and from 2784 to 3242 during anammox process, highlighting the increase in complexity of DON after undergoing both processes. DON with high saturation and aliphatic structures was removed by A/O process, whereas highly unsaturated and aromatic structures were removed by anammox process. For DON without S atom, Lignin‐like and tannin‐like ones were resistant to both processes and protein‐like and condensed aromatic structures were resistant to anammox process. The complementarity of these two processes provided a sequential combination with sufficient theoretical support to improve DON removal efficiency. Practitioner points Molecular components of dissolved organic nitrogen characterized by ESI FT–ICR MS. DON removal preferences of A/O and anammox processes evaluated. A/O and anammox processes are effective to remove aliphatic and aromatic DON, respectively. Complementarity in removal preferences of A/O and anammox processes can remove recalcitrant DON of each other. Sequential A/O and anammox processes can improve DON removal.

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

“…The numbers of the unique DON formulas from the two phases were 2072 and 1874, respectively (Table S2). Both DON samples had relatively low MW wa values (around 375), which were similar to that of DON from A/O or anammox processes . Specifically, the DBE wa decreased from 8.48 to 8.19 after PBS dosing, indicating the increased saturation feature of DON in the SNAD effluent.…”

“…The nitrogen-containing compounds include lipids (label 1, 1.5 ≤ H/C ≤ 2.0, O/C ≤ 0.3); proteins (label 2, 1.5 ≤ H/C ≤ 2.2, 0.3 ≤ O/C ≤ 0.67); lignins/carboxylic rich alicyclic molecules (CRAM) (label 3, 0.7 ≤ H/C ≤ 1.5, 0.1 ≤ O/C ≤ 0.67); carbohydrates (label 4, 1.5 ≤ H/C ≤ 2.4, 0.67 ≤ O/C ≤ 1.2); unsaturated hydrocarbons (label 5, 0.7 ≤ H/C ≤ 1.5, O/C ≤ 0.1); condensed aromatic structures (label 6, 0.2 ≤ H/C ≤ 0.7, O/C ≤ 0.67); and tannins (label 7, 0.6 ≤ H/C ≤ 1.5, 0.67 ≤ O/C ≤ 1.0). The detailed calculations of average double-bond equivalent (DBE wa ), average molecular weight (MW wa ), average modified aromaticity index (AI mod,wa ), and average ratios of oxygen-to-carbon (O/C wa ) and hydrogen-to-carbon (H/C wa ) could be found elsewhere …”

“…The detailed calculations of average double-bond equivalent (DBE wa ), average molecular weight (MW wa ), average modified aromaticity index (AI mod,wa ), and average ratios of oxygen-to-carbon (O/C wa ) and hydrogen-tocarbon (H/C wa ) could be found elsewhere. 23 2.6. Other Analytical Methods.…”