Abstract: A psychrotolerant bacterium strain W4 was isolated from active sludge and its nitrogen-removal capability at 5, 15, and 25 ℃ was evaluated. Results showed that W4 is affiliated to Pseudomonas, and could grow at 4 to 42 ℃, 0 to 30 g·L^-1 NaCl, and pH 6 to 9. At 5 ℃, strain W4 removed 74.3% of NH₄⁺-N (initial concentration of 76.0 mg·L^-1) within 72 h, corresponding to an average nitrogen-removal rate of 0.78 mg·L^-1·h^-1. Under aerobic conditions, up to 42.4% of nitrate (86.3 mg·L^-1) or 38.2% of nitrite (82.2 mg·L^-1) could be removed by strain W4. At 15 and 25 ℃, the nitrogen-removal efficiency was further improved, as evidenced by that more than 95% of ammonium, 66% of nitrate, and 69% of nitrite were removed. Strain W4 showed the activity of heterotrophic nitrification and aerobic denitrification (HA-ND). No nitrite accumulation was observed during nitrification process. The HA-ND capability by strain W4 justifies the potential in the treatment of inorganic nitrogen pollution under meso to psychrophilic conditions. Our findings help enrich psychrotolerant nitrogen-removing microbial resources, and contribute to the nitrogen pollution treatments through HA-ND process.

Key words: heterotrophic nitrification, aerobic denitrification, psychrotolerant, nitrogen removal.