A novel heterotrophic bacterium was isolated from activated sludge of a pig farm wastewater treatment plant and identified as Acinetobacter sp. T1. It exhibited efficient heterotrophic nitrification and aerobic denitrification capability to utilize ammonium, nitrate or nitrite as the sole nitrogen source, and their removal rates were 12.08, 5.53 and 1.69 mg/L/h, respectively. Furthermore, the optimal conditions for the heterotrophic nitrification process were sodium citrate as the carbon source, C/N mass ratio of 10, pH of 8.5 and dissolved oxygen (DO) concentration of 5.1 mg/L. Only trace amounts of nitrate and nitrite were observed during the process. When the aerobic tank of the A(2)O process of a pig farm wastewater treatment plant was inoculated with traditional activated sludge, the average removals of COD, NH4+-N and TN in the effluent were 30%, 15% and 16%, respectively, which was much lower than that of inoculated with strain T1, the increase was statistically significant, indicating a great potential of strain T1 for full-scale applications. (C) 2018, The Society for Biotechnology, Japan. All rights reserved.