Ammonium removal characteristics of heterotrophic nitrifying bacterium Pseudomonas stutzeri GEP-01 with potential for treatment of ammonium-rich wastewater.

A heterotrophic nitrifying bacterium was isolated from the activated sludge and identified as Pseudomonas stutzeri GEP-01. Strain GEP-01 exhibited an efficient heterotrophic nitrification capability and a high nitrogen utilization rate, 48 mg/L NH4+-N was removed after culturing for 24 h without NO2--N or NO3--N accumulation, and 64.7% of the NH4+-N was removed by heterotrophic nitrification. Single-factor experiments indicated that factors such as the carbon source, temperature, NH4+-N load, and inoculum size had significant effects on the ammonium removal efficiency of strain GEP-01. The preferred conditions for heterotrophic nitrification were sodium citrate, 30 °C, 40 mg/L NH4+-N, and 5% inoculum size. When the initial NH4+-N amounts were 100, 200, 500 and 1000 mg/L, the removal rates were approximately 100%, 93%, 90.4%, and 78.9%, respectively, and higher ammonium concentrations require longer culture time. Nitrogen balance demonstrated that 40% of the initial nitrogen was lost, which was probably removed in the form of gas products under optimum culture conditions, and 36.3% of NH4+-N was converted to biomass. When incubated (adding a small amount of sodium citrate as carbon source and no carbon source) in swine wastewater containing 835 mg/L of ammonium, the removal ratio reached 56.3% and 24.8%. Strain GEP-01 has potential applications in the treatment of ammonium-rich wastewater.