Hydrolyzed molasses was evaluated as an alternative carbon source in a biological nitrogen removal process. To increase biodegradability, molasses was acidified before thermohydrolyzation. The denitrification rate was 2.9-3.6 mg N/g VSS h with hydrolyzed molasses, in which the percentage of readily biodegradable substrate was 47.5%. To consider the hydrolysate as a carbon source, a sequencing batch reactor (SBR) was chosen to treat artificial municipal wastewater. During the 14 days (28 cycles) of operation, the SBR using hydrolyzed molasses as a carbon source showed 91.6 +/- 1.6% nitrogen removal, which was higher than that using methanol (85.3 +/- 2.0%) The results show that hydrolyzed molasses can be an economical and effective external carbon source for the nitrogen removal process. (c) 2005 Elsevier Ltd. All rights reserved.