Ammonium removal from source water is usually inhibited by insufficient carbon sources and low temperature in Northeastern China. A strain Y16 was isolated from oligotrophic niche and was identified as Acinetobacter sp. Y16. It demonstrated excellent capability for ammonium removal at 2 degrees C, and simultaneously produced nitrogen gas as the end product. About 66% of ammonium was removed after 36 h of incubation. Only trace accumulation of nitrate was observed during the process. The utilization of nitrite and nitrate as well as the existence of napA gene further proved the aerobic denitrification ability of strain Y16. Sodium acetate was the most favorable carbon source for ammonium oxidation by strain Y16. High rotation speed was beneficial for ammonium oxidation. Furthermore, strain Y16 could efficiently remove ammonium at low C/N ratio and low temperature conditions, which was advantageous for nitrogen removal from source water under cold temperatures. (c) 2013 Elsevier Ltd. All rights reserved.