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• Phosphorus content and removal efficiency should be considered to evaluate PAOs. • A novel highly-efficient strain C-13 with SNDPR ability was isolated. • A convenient way for nitrogen balance analysis was adopted to assess the HNAD. • Ammonium would be the optimal nitrogen source for assimilation and HNAD. Strain C-13, identified as an Acinetobacter sp. by homology searches, exhibited efficient simultaneous heterotrophic nitrification-aerobic denitrification phosphorus removal (SNDPR) abilities by nitrogen balance analysis and further confirmation of successful amplification of functional genes ppk , napA , and nirS. In addition, strain C-13 could utilize NH 4 +-N, NO 3 –-N, and NO 2 –-N as nitrogen sources, among which NH 4 +-N was indicated to be an excellent nitrogen source for assimilation and heterotrophic nitrification. Besides, the optimum conditions for nutrient removal were determined as follows: sodium acetate as the sole carbon source, C/N/P ratio of 100/10/2, pH = 7.5, and temperature of 30 °C. Meanwhile, the strain also showed the traditional features, such as release and the excess uptake of phosphate under anaerobic/aerobic conditions, with the highest phosphorus content of 5.01% after cultivation. Strain C-13 presents promising prospects for application in biological nutrient removal in wastewater treatment. [ABSTRACT FROM AUTHOR]

• Acinetobacter sp. YS2 was isolated from petrochemical wastewater treatment process. • Nitrifying and denitrifying enzyme genes were amplified successfully. • The proportion of aerobic denitrifiers reached 87.44% in the microbial community. • YS2 has potential application in the SND treatment for petrochemical wastewater. The ecological niche of aerobic denitrifiers in activated sludge is little studied, but this determines the performance of these bacteria in reactors. Acinetobacter sp. YS2 isolated from a treatment process for petrochemical wastewater and showed excellent nitrogen removal performance. In the nitrification and denitrification process, the removal efficiencies of NH 4 +-N and NO 3 −-N were 87.81% and 88.20% at 24 h, respectively, and nitrogen balance analysis indicated that the proportions of nitrogen removal by gaseous nitrogen were 37.58% and 46.45%, respectively. During simultaneous nitrification and denitrification (SND) treatment of synthetic petrochemical wastewater in a sequencing batch reactor (SBR), aerobic denitrifiers became the dominant species and the proportion reached 87.44% in the microbial community. The removal efficiencies of NH 4 +-N and TN were 99.46% and 80.36% over 5 days, respectively. This research has shown that aerobic denitrifiers can become the dominant species in the applications of SND treatment for petrochemical wastewater. [ABSTRACT FROM AUTHOR]