Response mechanism of denitrifying anaerobic methane oxidation microorganisms to ammonia

The dominant microorganisms in the denitrifying anaerobic methane oxidation (DAMO) process are primarily DAMO bacteria and DAMO archaea, which can simultaneously realise methane oxidation and denitrification. Ammonia is the primary form of nitrogen found in wastewater. This study focuses on a coexistence system that contains both DAMO bacteria and DAMO archaea (DAMO co-system). The short- and long-term effects of NH4+-N on the DAMO co-system were investigated at both the macro level (such as denitrification performance) and the micro level (such as microbial structure and community). Short-term experimental studies demonstrated that the safe concentration of ammonia for this system was 250 mg N L-1. When the ammonia concentration was 500 mg N L-1, the nitrogen removal efficiency was significantly inhibited. With an increase in concentration and an extension of time, the inhibitory effect of ammonia was enhanced. Long-term experimental studies showed that the nitrogen removal performance of DAMO was completely inhibited when the ammonia concentration reached 1000 mg N L-1 and that ammonia had a toxic accumulation effect on the DAMO co-system. The results of the pH experimental study demonstrated that free ammonia (FA) was the limiting factor in the alkaline condition, while ionised NH4+ was the limiting factor in neutral and acidic conditions. Scanning electron microscopy (SEM) demonstrated that the microbes in the DAMO co-system shrank after short-term exposure and that the microorganisms shrank in the shape of polygons. High-throughput sequencing analysis demonstrated that the community structure of the DAMO co-system changed substantially, and the species diversity and abundance decreased distinctly after long-term inhibition. A genus analysis indicated that the reduction in Nitrospirae may be an internal reason for the decrease in the denitrification performance of the DAMO co-system.