Promotion of heterotrophic nitrification-aerobic denitrification by nitrite and efficient removal of total nitrogen of strain EN-F2

The inhibition of heterotrophic nitrification-aerobic denitrification (HN-AD) process and low efficiency of total nitrogen conversion under nitrite stress were overcome by strain EN-F2. Results demonstrated that nitrite addition increased total nitrogen conversion to 91.36% and 87.02% for ammonium and nitrate systems, respectively, representing improvements of 5.61% and 15.41%. This enhancement is likely due to the simultaneous acceleration of cell growth, and consumption of ammonium and nitrate. Furthermore, 10 mg/L of hydroxylamine could be almost completely oxidized in a wide range of environmental conditions in the presence of 50 mg/L nitrite, and 100% and 89.82% of nitrite and total nitrogen could be degraded under the conditions of 25 °C, sodium succinate, 7.40 mg/L of dissolved oxygen, C/N ratio 20, initial pH 7.40–7.80 and inoculation quantity of 0.5 × 10⁸ CFU/mL. Altogether, the HN-AD performance of strain EN-F2 can be promoted by nitrite, and no nitrate and hydroxylamine accumulation were found.