Objective  Aiming at the problems of ammonium-rich and low denitrification efficiency in landfill leachate wastewater, a heterotrophic nitrification bacterium was enriched and isolated from the activated sludge of landfill leachate biochemical reaction tank.

Method  By means of morphological observation, physiological and biochemical identification, 16S rDNA gene sequence alignment and phylogenetic tree construction, the effects of different inoculation amount, initial pH, temperature, shaking speed and carbon source type on the denitrification effect of the strain were studied. The strain was inoculated into landfill leachate wastewater to evaluate its ability of heterotrophic nitrification.

Result  The isolated heterotrophic nitrobacteria strain was Acinetobacter sp., named XJ-1. After single factor optimization, strain XJ-1 could grow in the medium with sodium acetate as the sole carbon source and carry out heterotrophic nitrification. When the inoculation amount was 6%, with initial pH 7.5, temperature at 30 ℃, and the shaking speed of incubator maintained at 150 r/min, the highest ammonia nitrogen degradation rate was obtained; while strain XJ-1 was inoculated into the sterilized landfill leachate wastewater, after 96 h cultivation under the optimal conditions, the initial concentration of ammonia nitrogen (NH₄⁺-N) decreased from 545.91 mg/L to 317.58 mg/L, the NH₄⁺-N degradation rate reached 62.82%, and the intermediate products such as nitrite nitrogen (NO₂^--N) and nitrate nitrogen (NO₃^--N) did not accumulate significantly.

Conclusion  Strain XJ-1 has certain heterotrophic nitrification characteristics, and it has application value in the treatment of landfill leachate wastewater.