Experimental investigation and mathematical modeling of the competition among the fast-growing “r-strategists” and the slow-growing “K-strategists” ammonium-oxidizing bacteria and nitrite-oxidizing bacteria in nitrification

[Display omitted] •Fast-growing “r-strategists” AOB and NOB could be enriched in SBR.•The DO concentration and SRT affected the dominant nitrifier species.•r/K AOB and NOB competition revealed by the model simulation. Based on their differences in the kinetic values, the nitrifiers could be classified into the fast-growing “r-strategists” and the slow-growing “K-strategists” bacteria. However, the difference in the kinetic values originated not only from the intrinsic differences among the nitrifier species, but also from other factors, i.e. sludge floc morphology, and the environment in which the nitrifiers were cultivated. It is not clear how these factors interact and affect the measured kinetic parameters and the competition among the “r-strategists” and the “K-strategists” bacteria. In this study, the kinetic parameters of nitrifiers cultivated in the SBR (sequencing batch reactor) under different substrate concentrations were monitored, together with the identification of nitrifier species and sludge floc morphology characterization. The results showed that the r-AOB and r-NOB (“r-strategists” ammonium-oxidizing bacteria and nitrite-oxidizing bacteria, i.e., Nitrosomonas and Nitrospira) were the dominant nitrifiers in the SBR reactor. A mathematical model describing the competition between r/K AOB and NOB showed that r-AOB and r-NOB could be enriched in the SBR. The experimental investigation supported the model simulation results. The model simulation also revealed that the different r/K AOB and NOB species could be enriched in different DO concentrations and SRT conditions, which could be manipulated to promote the growth of r-AOB and NO2− accumulation for the autotrophic nitrogen removal using ANAMMX.