High performance nitrogen removal through integrating denitrifying anaerobic methane oxidation and Anammox: from...

Integrating denitrifying anaerobic methane oxidation (DAMO) with Anammox provides alternative solutions to simultaneously remove nitrogen and mitigate methane emission from wastewater treatment. However, the practical application of DAMO has been greatly limited by slow-growing DAMO microorganisms living on low-solubility gaseous methane. In this work, DAMO and Anammox co-cultures were fast enriched using high concentration of mixed sludges from various environments, and achieved nitrogen removal rate of 76.7 mg NH₄⁺-N L^-1 d^-1 and 87.9 mg NO₃^--N L^-1 d^-1 on Day 178. Subsequently, nitrogen removal rate significantly decreased but recovered quickly through increasing methane flushing frequency, indicating methane availability could be the limiting factor of DAMO activity. Thus, this work developed a novel Membrane Aerated Membrane Bioreactor (MAMBR), which equipped with gas permeable membrane for efficient methane delivery and ultrafiltration membrane for complete biomass retention. After inoculated with enriched sludge, nitrogen removal rates of MAMBR were significantly enhanced to 126.9 mg NH₄⁺-N L^-1 d^-1 and 158.8 mg NO₃^--N L^-1 d^-1 by membrane aeration in batch test. Finally, the MAMBR was continuously fed with synthetic wastewater containing ammonium and nitrite to mimic the effluent from partial nitritation. When steady state with nitrogen loading rate of 2500 mg N L^-1 d^-1 was reached, the MAMBR achieved total nitrogen removal of 2496.7 mg N L^-1 d^-1, with negligible nitrate in effluent (~6.5 mg NO₃^--N L^-1). 16S rRNA amplicon sequencing and fluorescence in situ hybridization revealed the microbial community dynamics during enrichment and application. The high performance of nitrogen removal (2.5 kg N m^-3 d^-1) within 200 days operation and excellent biomass retention capacity (8.67 kg VSS m^-3) makes the MAMBR promising for practical application of DAMO and Anammox in wastewater treatment.