Evaluation of simultaneous nitrification and denitrification under controlled conditions by an aerobic denitrifier culture

• Paracoccus versutus LYM could simultaneously remove NH4+ and NO3−.
• Fe2+ and carbon source benefit NO2− further conversion.
• NH4+ was critical for P. versutus LYM reducing NO2−.

Paracoccus versutus LYM was characterized with the ability of simultaneous nitrification and denitrification (SND) in presence of NH4+-N and NO3−-N (140 mg/L-N each). However, there was approximate 95.80 mg/L NO2−-N left during SND process. Fe2+ was added in the SND medium and it benefited bacterial growth and further converted NO2−-N a little. Besides, remaining NO2−-N could be completely reduced by adding carbon donors in presence of NH4+-N and NO3−-N, whose converting efficiencies also reached 97.09% and 96.34%, respectively. And N2 stayed as the main product of SND process. While NO2−-N and NH4+-N were present simultaneously, strain LYM could also remove nitrogen compounds thoroughly with sufficient carbon source. But there was no NO2−-N reduced as sole nitrogen source in the medium even if C/N ratio reached as high as 30.