Effect of substrate availability on nitrous oxide production by deammonification processes under anoxic conditions

Abstract

SummaryDue to its high global warming potential, nitrous oxide (N2O) emissions from wastewater treatment processes have recently received a high degree of attention. Nevertheless, there is still a lack of information regarding the microbiological processes leading to N2O production. In this study, two lab‐scale sequencing batch reactors were operated with deammonification biomass to investigate the role of denitrification and the influence of substrate availability regarding N2O formation during the anoxic phase of deammonification. Three different operational phases were established: within the first phase conversion by anammox was favoured and after a transition phase, denitrification activity was promoted. Low nitrous oxide production was observed during stable operation aiming for anammox conversion. Pulsed inflow of the wastewater containing ammonium (NH4+) and nitrite (NO2‐) led to increased N2O production rates. Within the period of denitrification as dominating nitrogen conversion process, the nitrous oxide concentration level was higher during continuous inflow conditions, but the reaction to pulsed inflow was less pronounced. The results indicated that denitrification was responsible for N2O formation from the deammonification biomass. Operational settings to achieve suppression of denitrification processes to a large extend were deducted from the results of the experiments.

Aeration Strategies To Mitigate Nitrous Oxide Emissions from Single-Stage Nitritation/Anammox Reactors

“…12 However, NO production has been linked to higher NO 2 − concentrations in the presence of NH 4 + and to increases in the relative transcription of autotrophic denitrification genes by N. europaea 19718. 48 It is in agreement with ammonium oxidation being the electron source to the expected increase in NO 2 − reduction activity and nirK expression of AOB, 11,49 which followed by NO reduction would result in liquid N 2 O accumulation. Therefore, the presence of both NO 2…”

“…on N 2 O production but not on individual mechanisms. 8,9,11,16,18,40 In 2-stage nitritation/anammox systems, most emissions derive from the nitritating stage, where AOB are dominant. 10,46,54 The reaction conditions in our study, such as aerated/nonaerated periods, carbon-limited feeding, nonlimiting FA and NO 3 − , support possible N 2 O production by all known pathways: incomplete denitrification, nitrifier denitrification, and hydroxylamine oxidation.…”

“…7 Documented N 2 O emissions from lab and full-scale single-stage nitritation/anammox systems have been higher than those measured from conventional BNR processes, 2,8−10 potentially offsetting the benefit associated with their energy savings and corresponding CO 2 emission reductions. 11 How N 2 O emissions from nitritation/anammox treatment systems depend on design or operation has not been carefully examined. Such information is needed to propose and evaluate mitigation measures geared toward process optimization or alternative designs.…”

“…Contributions from wastewater treatment to anthropogenic N 2 O emissions are considered by the IPCC, but the emission factors used in this assessment likely underestimate true N 2 O emissions. ,, Furthermore, the total greenhouse gas (GHG) footprint of a WWTP is most sensitive to its N 2 O emissions . Documented N 2 O emissions from lab and full-scale single-stage nitritation/anammox systems have been higher than those measured from conventional BNR processes, ,− potentially offsetting the benefit associated with their energy savings and corresponding CO 2 emission reductions . How N 2 O emissions from nitritation/anammox treatment systems depend on design or operation has not been carefully examined.…”

Atmospheric impact of nitrous oxide uptake by boreal forest soils can be comparable to that of methane uptake

“…Nitrous oxide is reduced to N 2 by nitrous oxide reductase (N 2 OR). High availability of NO 3 − , low pH, and low soil water content (high O 2 availability), are among the factors decreasing the N 2 OR activity and increasing the ratio of N 2 O to N 2 (N 2 O + N 2 ) in denitrification (Weier et al 1993;Tate 1995;Thomas et al 1994;Schneider et al 2012). In contrast, low NO 3 − availability and high soil water content favour the N 2 OR activity over the previous reductive steps, which could lead to net N 2 O consumption (uptake of N 2 O from the atmosphere) (Chapuis-Lardy et al 2007).…”