In this study, a novel denitrification reactor is used to treat sludge dewatering liquor, where the co-occurrence of sludge fermentation and nitrate reduction was obtained. The system showed an efficient and stable nitrogen removal performance. When the effluent recycle ratio was 200%, TN and NH4+ removal efficiency was 99.6% and 83.5%, respectively. In addition, primary sludge could be well degraded in the novel system. Over 50% volatile suspended solid (VSS) of primary sludge was utilized, and the ratio of VSS/SS declined from 0.76 to 0.39. Further investigation with batch experiments revealed that, compared to conventional sludge fermentation, the integration of denitrification and fermentation was better at carbon production as well as the control of ammonium release. (C) 2011 Elsevier Ltd. All rights reserved.