Linking nitrous oxide emissions to population dynamics of nitrifying and denitrifying prokaryotes in four full-scale wastewater treatment plants

Ammonia-oxidizing bacteria (AOB), ammonia oxidizing archaea (AOA) and N2O-reducing denitrifiers were measured by quantitative real-time PCR (qPCR) in activated sludge samples from four full-scale wastewater treatment plants (WWTPs) in South Spain, and their abundances were linked to the generation of N2O in the samples using multivariate analysis (Non-metric multidimensional scaling, MDS, and BIO-ENV). The average abundances of AOA remained in similar orders of magnitude in all WWTPs (10(6) copies amoA/L activated sludge mixed liquor), while significant differences were detected for AOB (10(5)-10(9)copies amoA/L) and N2O-reducers (10(7)-10(10) copies nosZ/L). Average N2O emissions measured in activated sludge samples ranged from 0.10 +/- 0.05 to 6.49 +/- 8.89 mg N2O-N/h/L activated sludge, and were strongly correlated with increased abundances of AOB and lower counts of N2O-reducers. A significant contribution of AOA to N2O generation was unlikely, since their abundance correlated negatively to N2O emissions. AOB abundance was favoured by higher NOi and NOiconcentrations in the activated sludge. (C) 2018 Elsevier Ltd. All rights reserved.