Nitrogen removal by <i>Providencia rettgeri</i> strain YL with heterotrophic nitrification and aerobic denitrification

<p><i>Providencia rettgeri</i> strain YL shows the capability of nitrogen removal under sole aerobic conditions. By using isotope ratio mass spectrometry, <sup>15</sup>N-labelled N<sub>2</sub>O and N<sub>2</sub> were detected in aerobic batch cultures containing , or . Strain YL converted , and to produce more N<sub>2</sub>O than N<sub>2</sub> in the presence of . An <sup>15</sup>N isotope tracing experiment confirmed that the nitrogen removal pathway of strain YL was heterotrophic nitrification-aerobic denitrification. The optimal treatment conditions for nitrogen removal were pH of 8, C/N ratio of 12, temperature of 25°C and shaking speed of 105 rpm. A continuous aerobic bioreactor inoculated with strain YL was developed. With an influent concentration of 90–200 mg/L, the removal efficiency ranged from 80% to 97% and the total nitrogen removal efficiency ranged from 72% to 95%. The nitrogen balance in the continuous bioreactor revealed that approximately 35–52% of influent was denitrified aerobically to form gaseous nitrogen. These findings show that the <i>P</i>. <i>rettgeri</i> strain YL has potential application in wastewater treatment for nitrogen removal under sole aerobic conditions.</p>