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Anammox bacteria were exposed to 3,500 ppm nitric oxide (NO) in the gas phase to determine the effects of nitrogen oxides on anammox bacteria. The anammox bacteria were not inhibited by the high NO concentration but instead utilized it to oxidize additional ammonium to dinitrogen gas under conditions relevant to wastewater treatment.

The overall goal of this study was to determine the molecular and metabolic responses of chemostat cultures of model nitrifying bacteria to imposition of and recovery from transient anoxic conditions. Based on the study, a specific directionality in nitrous oxide (N2O) and nitric oxide (NO) production was demonstrated. N2O production was only observed during recovery to aerobic conditions after a period of anoxia and correlated positively with the degree of ammonia accumulation during anoxia. NO, on the other hand, was emitted mainly under anoxia. The production of NO was linked to a major imbalance in the expression of the nitrite reductase gene, which was overexpressed during transient anoxia. In contrast, genes coding for ammonia and hydroxylamine oxidation and nitric oxide reduction were generally under-expressed during transient anoxia. These results are different from the observed parallel expression and activity of nitrite and nitric oxide reductase in heterotrophic bacteria subjected to transient oxygen cycling. Unlike NO, the production of N2O could not be solely correlated to gene expression patterns and likely involved responses at the enzyme activity or metabolic levels. Based on experimental data, the propensity of the nitrifying cultures for N2O production is related to a shift in their metabolism from a low specific activity (q < qmax) toward the maximum specific activity (qmax). [ABSTRACT FROM AUTHOR]

Originally presented at the 1st IWA/WEF Wastewater Treatment Modelling Seminar (WWTmod 2008), this contribution has been updated to also include the valuable feedback that was received during the Modelling Seminar. This paper addresses a number of basic issues concerning the modelling of nitrite in key processes involved in biological wastewater water treatment. To this end, we review different model concepts (together with model structures and corresponding parameter sets) proposed for processes such as two-step nitrification/denitrification, anaerobic ammonium oxidation and phosphorus uptake processes. After critically discussing these models with respect to their assumptions and parameter sets, common points of agreement as well as disagreement were elucidated. From this discussion a general picture of the state-of-the-art in the modelling of nitrite is provided. Taking this into account, a number of recommendations are provided to focus further research and development on nitrite modelling in biological wastewater treatment. [ABSTRACT FROM AUTHOR]

Abstract: Oxidation of high-strength ammonium wastewater can lead to exceptionally high nitrite concentrations; therefore, the effect of high nitrite concentration (>400mM) was studied using an ammonium-oxidizing enrichment culture in a batch reactor. Ammonium was fed to the reactor in portions of 40–150mM until ammonium oxidation rates decreased and finally stopped. Activity was restored by replacing half of the medium, while biomass was retained by a membrane. The ammonium-oxidizing population obtained was able to oxidize ammonium at nitrite concentrations of up to 500mM. The maximum specific oxidation activity of the culture in batch test was about 0.040mmol O2 g−1 proteinmin−1 and the K s value was 1.5mM ammonium. In these tests, half of the maximum oxidation activity was still present at a concentration of 600mM nitrite and approximately 10% residual activity could still be measured at 1200mM nitrite (pH 7.4), or as a free nitrous acid (FNA) concentration of 6.6mgl−1. Additional experiments showed that the inhibition was caused by nitrite and not by the high sodium chloride concentration of the medium. The added ammonium was mainly converted into nitrite and no nitrite oxidation was observed. In addition, gaseous nitrogen compounds were detected and mass balance calculations revealed a nitrogen loss of approximately 20% using this system. Phylogenetic analyses of 16S rRNA and ammonium monooxygenase (amoA) genes of the obtained enrichment culture showed that ammonium-oxidizing bacteria of the Nitrosomonas europaea/Nitrosococcus mobilis cluster dominated the two clone libraries. Approximately 25% of the 16S rRNA clones showed a similarity of 92% to Deinococcus-like organisms. Specific fluorescence in situ hybridization (FISH) probes confirmed that these microbes comprised 10–20% of the microbial community in the enrichment. The Deinococcus-like organisms were located around the Nitrosomonas clusters, but their role in the community is currently unresolved. [Copyright &y& Elsevier]

Nitric oxide (NO) and nitrous oxide (N2O) emissions from nitrifying ecosystems are a serious threat to the environment The factors influencing the emission and the responsible microorganisms and pathways were studied using a laboratory-scale nitrifying reactor system. The nitrifying culture was established at growth rates relevant to wastewater treatment plants (WWTPs). During stable ammonia oxidation, 0.03% of ammonium was emitted as NO and 2.8% was emitted as N2O. Although mixed cultures were used, clear responses in emission of ammonia oxidizing bacteria (AOB) could be detected and it was concluded that the denitrification pathway of AOB was the main source of the emissions. Emissions of nitrogen oxides in the system were strongly influenced by oxygen, nitrite, and ammonium concentrations. Steady state emission levels greatly underestimate the total emission, because changes in oxygen, nitrite, and ammonium concentrations induced a dramatic rise in NO and N2O emission. The data presented can be used as an indication for NO and N2O emission by AOB in plug-flow activated sludge systems, which is highly relevant because of the atmospheric impact and potential health risk of these compounds. [ABSTRACT FROM AUTHOR]

The effects of nitrogen oxides on anammox bacteria are not well known. Therefore, anammox bacteria were exposed to 3,500 ppm nitric oxide (NO) in the gas phase. The anammox bacteria were not inhibited by the high NO concentration but rather used it to oxidize additional ammonium to dinitrogen gas under conditions relevant to wastewater treatment. [ABSTRACT FROM AUTHOR]