Four anaerobic sequencing batch reactors (ASBRs) were used for hydrogen fermentation and fed with food waste (4.4 +/- 0.2% volatile solids (VS) containing 27 g carbohydrate-COD/L). The aim of this study was to investigate the effects of solids retention time (SRT) in the range 24160 h and hydraulic retention time (HRT) in the range 24-42 h. Achieving high SRT independent of HRT with internal sludge retention contributed to higher H-2 production than in previous studies using continuous stirred-tank reactor systems. The maximum H-2 production rate of 2.73 L H-2/(Ld) was estimated at an SRT of 126 h and HRTof 30 h, while the maximum H2 yield of 80.9 mL H-2/g VS (1.12 mol H-2/mol hexose(added)) occurred at an SRT of 126 h and HRT of 33 h. Furthermore, hydrogen fermentation facilitated organic acid conversion, alcohol conversion, and volatile suspended solid removal with efficiencies ranging from 29.6 to 46.3%, 4.1 to 14.6%, and 54.9 to 75.8%, respectively, which Were comparable to conventional acidogenic fermentation without H-2 production. (c) 2007 Elsevier Ltd. All rights reserved.