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

The goal of the study was to connect activated sludge microbiome data with nitrous oxide (N2O) production and nitrite (NO2-) accumulation patterns in a full-scale wastewater treatment plant (WWTP). We characterized the microbiome structures (using 16S rRNA gene amplicon sequencing) in several parallel activated sludge lines of a WWTP during high N2O emissions (up to 20% of the nitrogen load), with NO2- accumulation in 7 out of 9 parallel lines. Microbiomes in treatment lines with and without NO2- accumulation were compared with each other and the process performance data, including N2O monitoring data. Shifts in the nitrifying population appear particularly relevant for periods with NO2- accumulation and N2O peaks in WWTPs.