BACKGROUND Heterotrophic nitrifying bacteria (HNB) have rapid growth rate, high activity and strong anti-shock ability. These attributes are advantageous in engineering applications, yet the use of HNB is restricted by lack of clarity about the kinetics and metabolic mechanisms involved. Thus, nitrogen conversion characteristics, kinetics and N2O production of the HNB Pseudomonas putida YH were evaluated. RESULTS Strain YH exhibited superior heterotrophic nitrification-aerobic denitrification (HNAD) ability in treating nitrogenous wastewater, with maximum removal rates of 10.07, 8.86 and 8.78 mg L-1 h(-1) for NH4+-N, NO3--N and NO2--N, respectively. Mass balance analysis demonstrated that the removed TN was mainly due to bacterial assimilation (53-55%) and conversion into gaseous N-2 (34-39%), instead of nitrification intermediate accumulation and N2O emission. In addition, the kinetics of nitrogen degradation and cellular growth of strain YH exactly conformed to the modified Gompertz equation and the Logistic equation, respectively. Moreover, strain YH showed excellent adaptability to variations of temperature, pH, C:N ratio and initial NH4+-N concentration in terms of nitrogen removal and N2O emission. The highest NH4+-N removal rate was obtained at pH 7.0, temperature 30 degrees C and C:N ratio of 15. Furthermore, the heterotrophic nitrification ability was just partially deteriorated after the addition of inhibitors, which further proved the multiple metabolic pathways of heterotrophic nitrification by strain YH. CONCLUSION The results demonstrated that strain YH exhibited excellent abilities of HNAD, N2O emission control and tolerance to adverse conditions, indicating that strain YH can be an effective candidate for treating nitrogenous wastewater without secondary pollution. (c) 2019 Society of Chemical Industry