An experimental procedure for identifying the aerobic-phase biological source of nitrous oxide in anoxic–aerobic wastewater treatment systems

Abstract

This paper describes a relatively simple experimental procedure used to assess the relative contribution of autotrophic and heterotrophic organisms in the generation of aerobic-phase nitrous oxide from a mixed microbial population in a bench-scale, anoxic-aerobic, sequencing batch reactor (SBR) wastewater treatment system. The procedure eliminated ammonia oxidation from a "perturbation" cycle, while maintaining pH and dissolved oxygen levels similar to the "baseline" cycle. Nitrite and carbon oxidation were maintained during the perturbation cycle. Compared to more complex methods such as stable isotope labelling techniques, the described procedure is logistically simple and requires equipment readily available in most environmental engineering laboratories. When applied to an SBR system treating synthetic wastewater (influent ammonia N concentration = 160 mg/L), the experimental results strongly suggest that essentially all of the nitrous oxide produced during the aerobic phase of the cycle was generated by autotrophic, ammonia oxidizing organisms. Little, if any, nitrous oxide appeared to be generated by heterotrophic denitrification during the aerobic phase of the cycle.Resume: Le present article d6crit une procedure experimentale relativement simple utilizee pour evaluer la contribution relative des organismes autotrophes et heterotrophes dans la generation de I'oxyde d'azote en phase a6robie a partir d'une population microbienne mixte anoxique/aerobie, a echelle laboratoire, dans un systeme de traitement des eaux usees par reacteur discontinu sequentiel (RDS). La procedure a elimine I'oxydation de I'ammoniaque d'un cycle de « perturbation » tout en maintenant les niveaux de pH et d'oxygene dissous similaires a ceux du cycle de « reference ». L'oxydation des nitrites et du carbone a ete maintenue durant le cycle de perturbation. Par rapport a des methodes plus complexes, telles que les techniques d'etiquetage par isotopes stables, la procedure decrite est simple du point de vue logistique et demande des equipements aisement disponibles dans presque tous les laboratoires de genie environnemental. Lorsqu'ils sont appliques a un systeme RDS pour le traitement des eaux usees synthetiques (concentration en ammoniaque de I'influent = 160 mg N/L), les resultats experimentaux suggerent fortement que presque tout I'oxyde d'azote produit durant la phase aerobie du cycle ait ete genere par des organismes autotrophes oxydant I'ammoniaque. Peu ou pas d'oxyde d'azote semblait etre genere par denitrification heterotrophe durant la phase aerobie du cycle.

Effect of anoxic/aerobic phase fraction on N2O emission in a sequencing batch reactor under low temperature

“…This was because the predenitrification process used in this study created an optimum circumstance for denitrification, and the N 2 O produced was reduced to N 2 immediately by nitrous oxide reductase (N 2 OR). This result was similar to that of Shiskowski et al (2004).…”

Effect of operational modes on nitrogen removal and nitrous oxide emission in the process of simultaneous nitrification and denitrification

“…In the anoxic-aerobic SND, N 2 O from anoxic stage was relatively insignificant demonstrating that the anoxic stage provided an optimum circumstance for denitrifying bacteria. This result was similar to that of Shiskowski et al [36] and Hu et al [16]. It is likely that N 2 O produced from conventional denitrification was quite low since the reduction of N 2 O to N 2 was soon by nitrous oxide reductase.…”

Nitrous oxide monitoring for nitrifying activated sludge aeration control: A simulation study

“…Present understanding is that the dominant source of N 2 O in low dissolved oxygen conditions (as a result of inhibition of the normal metabolic pathways) is autotrophic nitrifying bacteria (Shiskowski et al, 2004). Therefore, variations in the off-gas N 2 O concentrations should only be observed when there are changes in the level of metabolic inhibition experienced by these bacteria.…”