Heterotrophs are key contributors to nitrous oxide production in activated sludge under low C‐to‐N ratios during nitrification—Batch experiments and modeling

Abstract

Nitrous oxide (N O), a by-product of biological nitrogen removal during wastewater treatment, is produced by ammonia-oxidizing bacteria (AOB) and heterotrophic denitrifying bacteria (HB). Mathematical models are used to predict N O emissions, often including AOB as the main N O producer. Several model structures have been proposed without consensus calibration procedures. Here, we present a new experimental design that was used to calibrate AOB-driven N O dynamics of a mixed culture. Even though AOB activity was favoured with respect to HB, oxygen uptake rates indicated HB activity. Hence, rigorous experimental design for calibration of autotrophic N O production from mixed cultures is essential. The proposed N O production pathways were examined using five alternative process models confronted with experimental data inferred. Individually, the autotrophic and heterotrophic denitrification pathway could describe the observed data. In the best-fit model, which combined two denitrification pathways, the heterotrophic was stronger than the autotrophic contribution to N O production. Importantly, the individual contribution of autotrophic and heterotrophic to the total N O pool could not be unambiguously elucidated solely based on bulk N O measurements. Data on NO would increase the practical identifiability of N O production pathways. Biotechnol. Bioeng. 2017;114: 132-140. © 2016 Wiley Periodicals, Inc.

Low nitrous oxide production through nitrifier-denitrification in intermittent-feed high-rate nitritation reactors

“…There are two main pathways involved in N 2 O produced by AOB: (a) the reduction of NO 2 to N 2 O via nitric oxide (NO), known as nitrifier denitrification (ND) (Ishii et al, 2014;Kim et al, 2010;Wrage et al, 2001) and (b) N 2 O as a side product during incomplete oxidation of hydroxylamine (NH 2 OH) to NO 2 - (Law et al, 2012;Poughon et al, 2001;Tallec et al, 2006), known as hydroxylamine oxidation. Furthermore, denitrifying bacteria can be as important as AOB in the production of N 2 O under very low C/N conditions (Domingo-Félez et al, 2017). During heterotrophic denitrification (HD), N 2 O is an obligate intermediate and is produced during incomplete denitrification.…”

Regulation of key N2O production mechanisms during biological water treatment

“…A model considering the ND and HD pathways predicted N 2 O dynamics from nitrifying batch tests. However, for the same overall N 2 O fit the NO emissions and N 2 O pathway contributions varied greatly when NO affinities were varied within literature range (NO = 0.2 -4.0% NO/N 2 O, ND = -56%) [72]. The simultaneous calibration of intermediates such as NO or NH OH will increase the reliability of N 2 O simulations and pathway contributions [43,70] Thus, the combination of molecular ecological, computational and isotopic analysis approaches seems essential to improving our understanding of N 2 O pathways in water treatment systems, and knowledge gleaned from other environmental systems (e.g.…”

Identification of Nitrous Oxide Generation in Subsurface Wastewater Infiltration System Filled With Mixed Matrix

“…During nitrification (which occurs in the upper layers), N 2 O can be generated due to the oxidation of NH 4 + -N and hydroxylamine (NH 2 OH) (Sun et al, 2018). When the dissolved oxygen availability is limited, NO 2 --N accumulates and exerts toxicity to microbial cells (Domingo-Félez et al, 2017). In this case, heterogeneous nitrite reductase is produced and reduces NO 2 --N to N 2 O (Zhang et al, 2009;Lyu et al, 2017).…”

“…Due to the lack of nutrients and electron acceptorduring the "rest" period (i.e. the drying period)(Domingo-Félez et al, 2017),…”