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A novel biological nitrogen removal process can be developed based on the newly discovered nitrite-dependent anaerobic methane oxidation (n-damo) process. In this work, the short- and long-term effects of mineral nutrients on the n-damo process were investigated by single-factor and orthogonal experiments, respectively. The pH buffering capacities of different media were determined by acid–base titration. KHCO 3 and KH 2 PO 4 greatly influenced the activity of n-damo bacteria and the pH changes of the media. An improved n-damo medium was proposed, containing 0.3 g L −1 CaCl 2 , 0.2 g L −1 MgSO 4 , 0.3 g L −1 KH 2 PO 4 and 0.2 g L −1 KHCO 3 . Moreover, the presence of 1% of CO 2 in gas could maintain the pH near neutral in the improved medium, which was first estimated in theory and then verified in practice. Finally, these results were applied in an n-damo reactor. The nitrogen removal rate was slightly increased (from 10.0 ± 1.2 to 10.8 ± 1.4 mg N L −1 d −1 ), and the pH was quite stable after the improvement (daily changes from 0.58 ± 0.05 to 0.11 ± 0.02). [ABSTRACT FROM AUTHOR]

Nitrite-dependent anaerobic methane oxidation (n-damo) is a potential bioprocess for treating nitrogen-containing wastewater. This process uses methane, an inexpensive and nontoxic end-product of anaerobic digestion, as an external electron donor. However, the low turnover rate and slow growth rate of n-damo functional bacteria limit the practical application of this process. In the present study, the short- and long-term effects of variations in trace metal concentrations on n-damo bacteria were investigated, and the concentrations of trace metal elements of medium were improved. The results were subsequently verified by a group of long-term inoculations (90 days) and were applied in a sequencing batch reactor (SBR) (84 days). The results indicated that iron (Fe(II)) and copper (Cu(II)) (20 and 10 μmol L −1 , respectively) significantly stimulated the activity and the growth of n-damo bacteria, whereas other trace metal elements, including zinc (Zn), molybdenum (Mo), cobalt (Co), manganese (Mn), and nickel (Ni), had no significant effect on n-damo bacteria in the tested concentration ranges. Interestingly, fluorescence in situ hybridization (FISH) showed that a large number of dense, large aggregates (10–50 μm) of n-damo bacteria were formed by cell adhesion in the SBR reactor after using the improved medium, and to our knowledge this is the first discovery of large aggregates of n-damo bacteria. [ABSTRACT FROM AUTHOR]