The strain SFA13, isolated from Songhua River, demonstrates ability to convert ammonium to nitrogen under aerobic conditions at low temperature. On the basis of 16S rRNA gene sequence, the strain SFA13 was a species in genera Microbacterium. The isolate showed unusual ability of autotrophic nitrification with the ratio of 0.11 mg NH4+N/L/h at 5 degrees C. Ammonium was consumed by the strain SFA13 with the biodegradation of organic carbon and without nitrite or nitrate accumulation. NO3--N or NO2--N was reduced by the strain SFA13. The denitrification ratio was 0.24 mg NO3--N/L/h. Hydroxylamine oxidase, nitrite reductase and nitrate reductase were detectable. The putative nitrogen removal process by the strain SFA13 was as follows: NH4+-> NH2OH -> NO2--> NO3-, then NO3--> NO2--> N-2. Biological activated carbon attached with the strain SFA13 could effectively remove ammonium in surface water with the rate of 2.68 +/- 0.27-3.16 +/- 0.25 mg NH4+-N/L/h at C/N 2-10, temperature 10 degrees C, and DO >5.2 mg/L. (C) 2013 Elsevier Ltd. All rights reserved.