Efficient nitrogen removal by simultaneous heterotrophic nitrifying-aerobic denitrifying bacterium in a purification tank bioreactor amended with two-stage dissolved oxygen control

[Display omitted] •Alternating DO levels in PTBR achieved 95% TN removal of domestic sewage by KSND.•Anaerote adversely affected nitrification of KSND, but conducive to denitrification.•Transcription analysis revealed correlation between DO level and genes expression.•With two-stage DO control, KSND removed 88% TN from low-C/N domestic sewage in 180-d. Nitrogen removal performance of a simultaneous heterotrophic nitrifying-aerobic denitrifying (SND) bacterium (KSND) in a purification tank bioreactor (PTBR) amended with two-stage dissolved oxygen (DO) control was investigated. NH4+–N and total nitrogen (TN) removal efficiencies under aerobic conditions for domestic wastewater treatment were 97.12% and 52.64%, respectively. Under serial aerobic (DO > 4.0 mg/L) and anaerobic (DO