Ethylene-vinyl acetate (EVA) copolymer was used to immobilize H(2)-producing sewage sludge for H(2) production in a three-phase fluidized bed reactor (FBR). The FBR with an immobilized cell packing ratio of 10% (v/v) and a liquid recycle rate of 5 I/min (23% bed expansion) was optimal for dark H(2) fermentation. The performance of the FBR reactor fed with sucrose-based synthetic medium was examined under various sucrose concentration (C(so)) and hydraulic retention time (HRT). The best volumetric H2 production rate of 1.80 +/- 0.02 H(2) I/h/I occurred at C(so)=40 g COD/I and 2h HRT, while the optimal H(2) yield (4.26 +/- 0.04 mol H(2)/mol sucrose) was obtained at C(so) = 20 g COD/I and 6 h HRT. The H(2) content in the biogas was stably maintained at 40% or above. The primary soluble metabolites were butyric acid and acetic acid, as both products together accounted for 74-83% of total soluble microbial products formed during dark H(2) fermentation. Crown Copyright (C) 2009 Published by Elsevier Ltd. All rights reserved.