Shift in activated sludge microbiomes associated with nitrite accumulation and high nitrous oxide emissions
Oona Kinnunen, Antonina Kruglova, Marlene Mark Jensen, Anna Kuokkanen, Barth F. Smets, Anna Mikola
Abstract
Nitrous oxide (N 2 O) emissions can constitute over half of the carbon footprint of a wastewater treatment plant (WWTP), and emission peaks frequently correlate with nitrite (NO 2 − ) concentrations. However, connections between the microbiome and high N 2 O and NO 2 − levels are not well-documented. Here, we characterize the microbiomes in several parallel lines of a WWTP during massive N 2 O emissions (20 % of influent nitrogen load) with prolonged NO 2 − accumulation in most lines, aiming to identify key differences between communities in lines with high and low NO 2 − concentrations. The abundance of nitrite-oxidizing bacteria (NOB) was extremely low in the lines with NO 2 − accumulation, which also had slightly lower abundances of ammonia-oxidizing bacteria (AOB). Some incomplete denitrifiers were more abundant in the lines with NO 2 − accumulation. Lines without NO 2 − had a higher relative abundance of filamentous bacteria and better floc formation. These findings confirmed our hypothesis that loss of NOB caused NO 2 − accumulation, inducing increased N 2 O emissions. AOB are suspected to be the main source of N 2 O during the studied period, with a likely contribution from heterotrophic denitrifiers . A few species were identified as interesting candidates for further study regarding their potential role in increased N 2 O emission from WWTPs . Long-term microbiome monitoring is necessary to understand the changes in the microbiome that might initiate NO 2 − accumulation and high N 2 O emissions.