Isolation of an aerobic denitrifying bacterial strain NS-2 from the activated sludge of piggery wastewater treatment systems in Taiwan possessing denitrification under 92% oxygen atmosphere

Aims: To isolate aerobic denitrifying bacteria which will be applied to piggery wastewater treatment facilities for enhanced nitrate and nitrite removal. Methods and Results: Nitrate-supplemented basal medium in airtight, crimp-sealed serum bottles containing an atmosphere of 92% oxygen was inoculated with denitrifiers, strains NS-2 and SM-3, and incubated at 30 degreesC. After 20 h, the concentration of nitrate was decreased rapidly by both NS-2 and SM-3. Nitrite production was almost zero during the whole experimental period for both strains. Nitrogen gas production peaked at the 20 h for both NS-2 (8.20 +/- 1.03 mmol l(-1)) and SM-3 (3.93 +/- 0.16 mmol l(-1)). Conclusions: Strain NS-2, which produced the highest N-2 concentration in this work, was identified as Pseudomonas stutzeri. This strain is the most capable of aerobic and anaerobic conversion of nitrate to N-2 without forming a nitrite intermediate. Significance and Impact of the Study: Strain NS-2 is highly promising for future application in in situ piggery wastewater treatment.