Nitrogen removal and metabolic pathway of Enterobacter cloacae DK-6

A heterotrophic nitrifier and aerobic denitrifier was isolated from chaff bedding of a pig farm and identified as Enterobacter cloacae DK-6. The strain DK-6 showed efficient nitrogen removal abilities under aerobic condition, with the ammonium-N (105.56mg/L), nitrate-N (101.70mg/L) and nitrite-N (86.19mg/L) removal efficiency of 86.98, 94.66 and 100% under aerobic condition, respectively. Further experiments demonstrated that the nitrate-N removal efficiency was improved and strain DK-6 preferred to utilize nitrite-N when ammonium-N, nitrate-N and nitrite-N were used as mixed nitrogen sources. Nitrogen balance showed ammonium-N removal was mainly achieved by assimilation in the process of nitrification, while nitrate-N removal was mainly realized through N2 loss and hardly no greenhouse gas (N2O) was generated during denitrification. Efficient nitrate-N removal occurs at sodium succinate as carbon source, carbon/nitrogen ratio of 8–10, dissolved oxygen concentration of 4.3–5.2 mg/L, pH of 6–7, temperature at 25–35 °C and initial nitrate-N concentration of 50–200 mg/L. Above results suggested strain DK-6 has significant potential involving in multiple nitrogen pollutants treatment of wastewater under aerobic condition and lower carbon/nitrogen ratio.