Achieving high nitrogen removal efficiency by optimizing nitrite-dependent anaerobic methane oxidation process with growth factors

Nitrite-dependent anaerobic methane oxidation (N-DAMO) is a newly discovered bioprocess which uses methane as electron donor to reduce nitrite into dinitrogen. It is a promising clean bioprocess for denitrification in wastewater treatment. However, the low reaction rate and slow growth rate of N-DAMO bacteria within NC10 phylum limit the application of the process. In this study, we chose vitamin, heme, nucleobase and betaine to investigate their short- and long-term effects on N-DAMO bacteria. The concentrations of the growth factors of medium were improved according to the short-term experiments. The results were subsequently verified via long-term inoculations and were applied in a magnetically stirred gas lift reactor (MSGLR). The results indicated that nucleobase and betaine (5.0 and 200 μg L^-1 , respectively) significantly stimulated the N-DAMO activity, whereas vitamin and heme had no significant effects in the tested concentration ranges. During the long-term incubation, N-DAMO bacteria continuously increased and finally achieved a relative abundance of 14.4% on day 300. Notably, larger aggregates of N-DAMO bacteria were observed at the end of the long-term incubation. And the nitrogen removal rate of the MSGLR increased to 70 mg N L^-1 day^-1 , with the total nitrogen removal efficiency over 99.0%. However, the addition of betaine introduced methyl into the reactors and this made methylotrophs account a considerable part of the bacterial community, which limited the enrichment degree of N-DAMO bacteria. This work will contribute to the engineering application and enrichment of N-DAMO bacteria.