Hybrid Nitrous Oxide Production from a Partial Nitrifying Bioreactor: Hydroxylamine Interactions with Nitrite

Abstract

The goal of this study was to elucidate the mechanisms of nitrous oxide (NO) production from a bioreactor for partial nitrification (PN). Ammonia-oxidizing bacteria (AOB) enriched from a sequencing batch reactor (SBR) were subjected to NO production pathway tests. The NO pathway test was initiated by supplying an inorganic medium to ensure an initial NH-N concentration of 160 mg-N/L, followed by NO (20 mg-N/L) and dual NHOH (each 17 mg-N/L) spikings to quantify isotopologs of gaseous NO (NO, NO, and NO). NO production was boosted by NHOH spiking, causing exponential increases in mRNA transcription levels of AOB functional genes encoding hydroxylamine oxidoreductase (haoA), nitrite reductase (nirK), and nitric oxide reductase (norB) genes. Predominant production of NO among NO isotopologs (46% of total produced NO) indicated that coupling of NHOH with NO produced NO via N-nitrosation hybrid reaction as a predominant pathway. Abiotic hybrid NO production was also observed in the absence of the AOB-enriched biomass, indicating multiple pathways for NO production in a PN bioreactor. The additional NO pathway test, where NH was spiked into 400 mg-N/L of NO concentration, confirmed that the hybrid NO production was a dominant pathway, accounting for approximately 51% of the total NO production.

Quantifying nitrous oxide production pathways in wastewater treatment systems using isotope technology – A critical review

“…This pathway was confirmed in WWTS very recently in a 15 Nlabeling study (Terada et al 2017). The two N atoms in N2O originate from an N atom from NO2and an N atom from NH2OH (Frame et al 2017, Stieglmeier et al 2014, Terada et al 2017. Recent studies showed that N2O produced via the N-nitrosation hybrid N2O production pathway can be significant (Harper Jr et al 2015, Soler-Jofra et al 2016, Terada et al 2017.…”

“…However, the reaction is often masked by biological N2O production (Heil et al 2014). This pathway was confirmed in WWTS very recently in a 15 Nlabeling study (Terada et al 2017). The two N atoms in N2O originate from an N atom from NO2and an N atom from NH2OH (Frame et al 2017, Stieglmeier et al 2014, Terada et al 2017.…”

“…During denitrification, N2O is emitted by both autotrophic AOB via the nitrifier denitrification pathway, and heterotrophic denitrifiers via the heterotrophic denitrification pathway (Kampschreur et al 2009b, Law et al 2012b. In addition, it has been realized more recently that the abiotic/biotic N-nitrosation hybrid N2O production pathway can also contribute significantly to the N2O emission under some extreme circumstances when NO2and NH2OH concentrations are high (Soler-Jofra et al 2016, Terada et al 2017.…”

“…In addition, N2O can also be formed chemically from NH2OH and NO2via abiotic reactions (Harper Jr et al 2015, Soler-Jofra et al 2016, Terada et al 2017. Different N2O production pathways often occur simultaneously.…”

Isotopic evidence for alteration of nitrous oxide emissions and producing pathways contribution under nitrifying conditions

“…Nitrification is the oxidation of ammonium to nitrite (NO2 -) via the intermediate hydroxylamine (NH2OH) conducted by ammonia oxidizers and the subsequent oxidation of NO2to nitrate (NO3 -) by nitrite oxidizers. During nitrification, N2O can be produced as reaction side-product from hydroxylamine oxidation by biotic, abiotic or hybrid processes (Caranto et al, 2016;Heil et al, 2015;Terada et al, 2017). 35…”