Denitrification of low concentrations of NO(3)-N (20 mg L(-1)), with methanol as an organic carbon source (COD:NO(3)-N = 6) in laboratory upflow sludge bed reactor (USB), was tested as a possibility for wastewater post-treatment. By gradual increase of volumetric loading (Bv) and hydraulic loading (gamma), anoxic biomass spontaneously granulated out even from flocculate activated sludge and from anaerobic granulated sludge as well. Anaerobic granulated biomass derived from high-rate anaerobic IC reactor was a far better inoculum for anoxic granulation and for denitrification in the USB reactor. The maximum level of Bv and gamma was remarkably higher with the use of anaerobic granulated inoculum, (19-22kg COD m(-3) d(-1); 3.2-3.7 kg NO(3)-N m(-3) d(-1); 2.8-3.2 m(3) m(-2) h(-1); SVI = 15 mL g(-1)) in comparison to inoculum from flocculate activated sludge (4.2-8.1 kg COD m(-3) d(-1); 0.7-1.4 kg NO(3)-N m(-3) d(-1); 0.7-1.15 m(3) m(-2) h(-1); SVI = 40-95 mL g(-1)). (C) 2009 Elsevier Ltd. All rights reserved.