Ammonium removal characteristics of an acid-resistant bacterium Acinetobacter sp. JR1 from pharmaceutical wastewater capable of heterotrophic nitrification-aerobic denitrification

[Display omitted] •A newly acid-resistant strain JR1 was isolated from pharmaceutical wastewater.•A high nitrogen removal could be achieved by JR1 under the acidic condition.•Nitrate began to be utilized as substitute N-source after exhausting of ammonium.•Ammonium was utilized through assimilation along with heterotrophic nitrification. A new acid-resistant bacterium Acinetobacter sp. JR1 was isolated, and its feasibility in nitrogen removal was investigated under acidic condition. Results show that JR1 indicated excellent ammonium and nitrate removal abilities with no accumulation of intermediates, and the maximum ammonium and nitrate removal efficiencies were 98.5% and 91.1%, respectively. Further experiments demonstrated that JR1 preferred to use ammonium with ammonium and nitrate as the mixed N-sources. For JR1, ammonium was assimilated directly as nutrients into cells and also converted into N2 through heterotrophic nitrification-aerobic denitrification. Under acidic condition, JR1 performed comparable nitrogen removal abilities to other strains under neutral or weak alkaline environment, and the efficient removal of ammonium occurred at pH 4.5–10, C/N 12–24, 20–40 °C, DO ≥4.72 mg/L, 0–1.5% of salinity, 10 mg/L Zn2+ or 20 mg/L Mn2+. All these make JR1 a promising candidate for treating acidic wastewater containing nitrogen.