Nitrogen removal by Providencia rettgeri strain YL with heterotrophic nitrification and aerobic denitrification

Providencia rettgeri strain YL shows the capability of nitrogen removal under sole aerobic conditions. By using isotope ratio mass spectrometry, 15N-labelled N2O and N2 were detected in aerobic batch cultures containing , or . Strain YL converted , and to produce more N2O than N2 in the presence of . An 15N 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 P. rettgeri strain YL has potential application in wastewater treatment for nitrogen removal under sole aerobic conditions.