A draft tube fluidized bed reactor (DTFBR) containing immobilized cell particles was designed to produce H-2 continuously. A synthetic polymer (silicone gel; SC) was used as the primary material to immobilize acclimated anaerobic sludge for H2 production in DTFBR with a working volume of 8 L. The DTFBR system was operated at a hydraulic retention time (HRT) of 2.2-8.9 h and an influent sucrose concentration (C-S) of 5-40 g COD/l. The results show that in general decreasing HRT or increasing sucrose concentration led to a marked increase in the volumetric H2 production rate (v(H2)), but a gradual decrease in the H2 yield (Y-H2). The best v(H2) (2.27 +/- 0.131/h/l) occurred at C-S = 40 g CODA and HRT = 2.2 h, whereas the highest Y-H2 (4.98 +/- 10.18 mol H-2/mol sucrose) was obtained at C-S = 40 g CODA and HRT = 8.9 h. The correlation between the production rate and the organic loading rate (OLR) can be satisfactorily described by Monod-type models. There was no universal trend of the dependence between the H-2 yield and OLR. The H-2 content in the biogas was stably maintained at over 40%. The major soluble products were butyric acid and acetic acid, as they accounted for 62-73% and 16-22% of total soluble microbial products (SMPs), respectively. The H-2-producing performance in the DTFBR system can be stably maintained and reproducible in long-term operations, while unstable operations can be quickly recovered via proper thermal treatment at 70-80 degrees C. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.