Improvement of mineral nutrient concentrations and pH control for the nitrite-dependent anaerobic methane oxidation process

• Short- and long-term effects of mineral nutrients on the n-damo were investigated.
• High levels of KHCO3 inhibited the n-damo process in short- and long-term tests.
• 1% CO2 in gas can finely control the pH near neutral in the improved medium.

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. KHCO3 and KH2PO4 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 CaCl2, 0.2 g L−1 MgSO4, 0.3 g L−1 KH2PO4 and 0.2 g L−1 KHCO3. Moreover, the presence of 1% of CO2 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).