The experiment was conducted to evaluate the performance of an upflow anaerobic sludge blanket (UASB) with granules for H-2 production from a sucroserich synthetic wastewater at various substrate concentrations (5.33-28.07 g-COD/L) and hydraulic retention times (HRTs) (3-30 h) for over 3 years. The kinetics of H2 production was evaluated, and the sludge yield and endogenous decay coefficient of the H-2-producing granules were estimated to be 0.334g-VSS/g-COD and 0.004/h, respectively. Based on Gibbsfree energy calculations, the formation thermodynamics of caproate, an important aqueous product, were analyzed. Experimental results showthatthe H-2 partial pressure in biogas decreased with increasing substrate concentration, but was not sensitive to the variation of HRT in a range of 6-22 h. The H-2 production rate increased with increasing substrate concentration, but decreased with increasing HRT. The H2 yield was in the range of 0.49-1.44 mol-H-2/Molglucose. Acetate, butyrate, caporate, and ethanol were the main aqueous products in the reactor, and their concentrations were dependent on both substrate concentration and HRT. An elevated substrate concentration resulted in a shift of fermentation from butyrate- to caporate-type in the reactor and the formation of caproate was dependent on the H-2 partial pressure. The 3-year experimental results demonstrate that H-2 could be produced continuously and stably from the acidogenic granule-based UASB reactor. (c) 2006 Wiley Periodicals, Inc.