Characterization of the facultative anaerobic Pseudomonas stutzeri strain HK13 to achieve efficient nitrate and nitrite removal

Abstract

A new facultative anaerobic denitrifier was isolated from anoxic activated sludge and identified as Pseudomonas stutzeri strain HK13. Single-factor experiments indicated that the optimal conditions for nitrate removal were a C/N ratio of 8, an initial pH of 7–10, a shaking speed of 100 rpm, and a temperature of 30–40 °C. When 100 mg/L NO3--N and NO2--N were used separately as sole nitrogen sources, the strain exhibited efficient denitrification ability with total nitrogen (TN) removal efficiencies of 98.22% and 98.58%, respectively, in 15 h with the corresponding maximum removal rates of 20.03 and 21.77 mg/L/h. And there was no nitrite accumulation finally in the nitrate denitrification system. In addition, 97.42% total oxidized nitrogen (TON) was removed at 20 °C and 93.46% NO3--N was reduced at 45 °C, suggesting that strain HK13 had a wide range of temperature and pH to adapt to the environment. Moreover, strain HK13 exhibited a notable ability to tolerate high nitrate loading (initial NO3--N > 450 mg/L) with a TON removal amount of over 200 mg/L/day. These findings demonstrate that strain HK13 is effective for nitrogen removal in wastewaters containing high concentrations of nitrate and nitrite.