A denitrification reactor packed with wood as a carbon source was operated using synthetic inorganic wastewater. The maximum denitrification rate was 62.4 g-NO(3)(-)/m(3)/day at HRT of 24 h. The nitrate removal continued after 1500 days. The denitrification efficiency was assumed to enhance sulfur denitrification via wood degradation by sulfate reduction. The achieved sulfate reduction rate was 468 mg-SO(4)(2-)/kg-dry weight wood/day after 419 days of operation. The sulfate reduction rate in the deep-layer biofilm inside the wood was higher than that in the total biofilm inside the wood. The sulfate-reducing bacteria segregated inside the wood. This study suggested that Desulfobulbus spp. and Desulfomicrobium spp. grown in the deep-layer degraded the wood incompletely, and the produced organic acids were utilized by the heterotrophic denitrifying bacteria, Desulfobacter spp. and Desulfonema spp., grown in the surface layer, and that these surface bacteria complete the degradation of the organic acids from the wood. (C) 2010 Elsevier Ltd. All rights reserved.