Physiological characteristics of predominant ammonia-oxidizing bacteria enriched from bioreactors with different influent supply regimes

• The effect of wastewater supply regime on nitritation performance was investigated.
• Intermittent NH4+ supply achieved higher nitritation than the continuous one.
• Different NH4+ supply enriched distinct ammonia-oxidizing bacteria (AOB).
• The AOB population exhibited distinct biokinetic properties with NH4+ as a driver.
• AOB selection by NH4+ control could be important for a cost-effective N removal.

Two acclimatized biomasses exposed to ammonium (NH4+) concentration of 600 mg N L−1, one from a completely stirred tank reactor (CSTR), the other from a sequencing batch reactor (SBR), were assayed for nitritation performance, predominant nitrifying bacterial population and nitrous oxide (N2O) production. By virtue of fluctuating and constant NH4+ concentrations respectively, the SBR and CSTR wastewater supply regimes were hypothesized to support different predominant ammonia-oxidizing bacteria (AOB) exhibiting distinct biokinetic properties. Nitritation efficiency (NO2−-N/NO2+3−-N) was higher in the SBR (89%) than the CSTR (30%) likely due to free ammonia and dissolved oxygen concentration. Quantitative fluorescence in situ hybridization (FISH) analyses revealed that fast-growing (r-strategist) AOB of halophilic and halotolerant Nitrosomonas lineage were more highly enriched in the SBR (76 ± 4.2%) than the CSTR (38 ± 6.0%). The CSTR predominantly enriched slow-growing (K-strategist) AOB Nitrosospira spp. (42 ± 1.9% versus 1.4 ± 0.8% in the SBR). Biokinetic parameter estimation consolidated the FISH result: the maximum growth rate and half-saturation coefficients for NH4+ were higher in the SBR (μmax = 0.92 day, KNH4+ = 28.9 mg N L−1) relative to the CSTR (μmax = 0.42 day, KNH4+ = 3.47 mg N L−1), suggesting that the extent of nitritation may be controlled by choice of wastewater influent operational regime, which itself determines predominant AOB. N2O production was a maximum of 25 times higher (10.2 mg N-N2O h−1 at 0.5 mg O2 L−1) in CSTR-enriched biomass than in SBR-enriched biomass (0.41 mg N-N2O h−1 at 0.5 mg O2 L−1).

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