Sewage sludge was acclimated to establish H-2-producing enrichment cultures for converting sucrose (20 g COD/l) into H-2 in an up-flow anaerobic sludge blanket (UASB) reactor. The operating hydraulic retention times (HRTs) were 24-4 h. The experimental results indicated that this UASB system could be used for hydrogen production. The hydrogen productivity was HRT dependent and nearly constant at the HRT of 8-20 h. However, it drastically decreased at an HRT of 4 or 24 h. The hydrogen production rate (HPR) and specific HPR peaked at the HRT of 8 h and drastically decreased at all other HRTs. At an HRT of 8 h, the average granular diameter peaked at 0.43 mm and each gram of biomass produced 53.5 mmol H-2/day with a hydrogen gas content of 42.4% (v/v). Butyrate and acetate were the main fermentation volatile fatty acids. The anaerobic granule sludge kinetic constants were endogenous decay coefficient (K-d) 0.1 day(-1) and yield coefficient (Y-g) 0.1 g VSS/g COD. The mean cell retention time was 22.2 h and the excess sludge discharge rate was 3.24 l/day. (C) 2003 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.