Denitrification kinetics indicates nitrous oxide uptake is unaffected by electron competition in Accumulibacter

Samarpita Roy; Pradhan Nirakar; N G How Yong; Wuertz Stefan

doi:10.1016/j.watres.2020.116557

Denitrification kinetics indicates nitrous oxide uptake is unaffected by electron competition in Accumulibacter

Water Res. 2021 Feb 1:189:116557. doi: 10.1016/j.watres.2020.116557. Epub 2020 Oct 26.

Authors

Samarpita Roy¹, Pradhan Nirakar², N G How Yong³, Wuertz Stefan⁴

Affiliations

¹ Singapore Centre for Environmental Life Sciences Engineering, National University of Singapore, Singapore 119077, Singapore. Electronic address: samarpita.roy@u.nus.edu.
² Singapore Centre for Environmental Life Sciences Engineering, Nanyang Technological University, Singapore 637551, Singapore. Electronic address: npradhan@hkbu.edu.hk.
³ NUS Environmental Research Institute, National University of Singapore, 5A Engineering Drive 1, Singapore 117411, Singapore. Electronic address: howyongng@nus.edu.sg.
⁴ Singapore Centre for Environmental Life Sciences Engineering, Nanyang Technological University, Singapore 637551, Singapore; School of Civil and Environmental Engineering, Nanyang Technological University, Singapore 639798, Singapore. Electronic address: swuertz@ntu.edu.sg.

PMID: 33220610
DOI: 10.1016/j.watres.2020.116557

Abstract

Denitrifying phosphorus removal is a cost and energy efficient treatment technology that relies on polyphosphate accumulating organisms (DPAOs) utilizing nitrate or nitrite as terminal electron acceptor. Denitrification is a multistep process, but many organisms do not possess the complete pathway, leading to the accumulation of intermediates such as nitrous oxide (N₂O), a potent greenhouse gas and ozone depleting substance. Candidatus Accumulibacter organisms are prevalent in denitrifying phosphorus removal processes and, according to genomic analyses, appear to vary in their denitrification abilities based on their lineage. Denitrification kinetics and nitrous oxide accumulation in the absence of inhibition from free nitrous acid is a strong indicator of denitrification capabilities of Accumulibacter exposed long-term to nitrate or nitrite as electron acceptor. Thus, we investigated the preferential use of the nitrogen oxides involved in denitrification and nitrous oxide accumulation in two enrichments of Accumulibacter and a competitor - the glycogen accumulating organism Candidatus Competibacter. We modified a metabolic model to predict phosphorus removal and denitrification rates when nitrate, nitrite or N₂O were added as electron acceptors in different combinations. Unlike previous studies, no N₂O accumulation was observed for Accumulibacter in the presence of multiple electron acceptors. Electron competition did not limit denitrification kinetics or lead to N₂O accumulation in Accumulibacter or Competibacter. Despite the presence of sufficient internal storage polymers (polyhydroxyalkanoates, or PHA) as energy source for each denitrification step, the extent of denitrification observed was dependent on the dominant organism in the enrichment. Accumulibacter showed complete denitrification, whereas Competibacter denitrification was limited to reduction of nitrate to nitrite. These findings indicate that DPAOs can contribute to lowering N₂O emissions in the presence of multiple electron acceptors under partial nitritation conditions.

Keywords: Accumulibacter; Electron competition; Free nitrous acid; Nitrous oxide (N(2)O) emission; Polyhydroxyalkanoates.

MeSH terms

Bioreactors
Denitrification*
Electrons
Kinetics
Nitrites
Nitrous Oxide*
Phosphorus

Substances

Nitrites
Phosphorus
Nitrous Oxide