Shift in activated sludge microbiomes associated with nitrite accumulation and high nitrous oxide emissions

Area of Science:

• Environmental microbiology
• Wastewater treatment technologies
• Greenhouse gas emissions

Background:

• Nitrous oxide (N2O) emissions are a significant contributor to wastewater treatment plant (WWTP) carbon footprints, often peaking with nitrite (NO2-) accumulation.
• The specific microbial drivers behind high N2O and NO2- levels in WWTPs remain poorly understood.

Purpose of the Study:

• To investigate the microbial community differences in WWTP lines exhibiting high versus low nitrite (NO2-) concentrations during substantial N2O emissions.
• To identify key microbial players associated with N2O production and NO2- accumulation.

Main Methods:

• Characterization of microbiomes in parallel WWTP lines experiencing significant N2O emissions and NO2- accumulation.
• Comparative analysis of microbial community structures in lines with differing NO2- levels.

Main Results:

• Lines with NO2- accumulation showed significantly lower abundance of nitrite-oxidizing bacteria (NOB) and slightly lower ammonia-oxidizing bacteria (AOB).
• Incomplete denitrifiers were more abundant in NO2--accumulating lines, while filamentous bacteria and better floc formation were observed in lines without NO2-.
• Ammonia-oxidizing bacteria (AOB) are suspected primary N2O sources, with potential contributions from heterotrophic denitrifiers.

Conclusions:

• The loss of NOB is confirmed as the cause of NO2- accumulation, leading to elevated N2O emissions.
• Specific microbial species warrant further investigation for their role in N2O generation in WWTPs.
• Continuous microbiome monitoring is crucial for predicting and mitigating N2O emissions and NO2- buildup.