Denitrification Characteristics, pH and Temperature Influence of an Aerobic Denitrifier

A high efficient aerobic denitrifying bacterium (G2) capable of rapid removal of NO₃ and NO₂ was isolated from activated sludge. The purpose of this work was to study the characteristics, pH and temperature effects of the isolated bacterium. The morphology of the isolated aerobic denitrifier G2 was a short bacillus, with average size of (0.3~0.6) mumtimes(1.4~3.0) mum. According to the 16S rDNA sequencing analysis, the isolated G2 was identified to be Paracoccus sp. The napA gene was cloned from G2. The gene was subunit of periplasmic nitrate reductase (NAR), which was considered to be important to aerobic denitrification. pH and temperature influenced the nitrogen metabolism and changed the growth of G2. Its nitrogen removal rate can reach more than 90 percent in natural pH and low alkali environment(pH =7~9), but G2 can not grow in acidic conditions. G2 showed stronger growth and better denitrification at 25degC ~ 35degC. And the nitrate and nitrite removal rate were 59.1 mg N-NO₃ ^- removed h^-1 g^-1 dry wt of cells and 52.6 mg NO₂ ^-- N removed h^-1 g^-1 dry wt of cells in optimal cultivation pH (pH = 7) and the best growth temperature (T = 30degC ).The data was significantly higher than that previously described in the literature. All the results revealed that the isolated G2 was able to rapid and effective aerobic nitrification. It had potential appliance value in actual natural pH and low alkali nitrogen-containing wastewater treating processes.