A pilot-scale high-rate dark fermentative hydrogen production plant has been established in the campus of Feng Chia University to develop biohydrogen production pilot-plant technology. This pilot-plant system is composed of two feedstock storage tanks (0.75 m(3) each), a nutrient storage tank (0.75 m(3)), a mixing tank (0.6 m(3)), an agitated granular sludge bed fermentor (working volume 0.4 m(3)), a gas-liquid-solid separator (0.4 m(3)) and a control panel. The seed mixed microflora was obtained from a lab-scale agitated granular sludge bed bioreactor. This pilot-scale fermentor was operated for 67 days at 35 degrees C, an organic loading rate (OLR) of 40-240 kg COD/m(3)/d, and the influent sucrose concentration of 20 and 40 kg COD/m(3). Both biogas and hydrogen production rates increased with increasing OLR. However, the biomass concentration (volatile suspended solids, VSS) only increased with an increasing OLR at an OLR range of 40-120 kg COD/m(3)/d, whereas it decreased when OLR was too high (i.e., 240 kg COD/m(3)/d). The biogas consisted mainly of H(2) and CO(2) with a H(2) content range of 23.2-37.8%. At an OLR of 240 kg COD/m(3)/d, the hydrogen content in biogas reached its maximum value of 37% with a hydrogen production rate (HPR) of 15.59 m(3)/m(3)/d and a hydrogen yield of 1.04 mol H(2)/mol sucrose. This HPR value is much higher than 5.26 m(3)/m(3)/d (fermented molasses substrate) and 1.56 m(3)/m(3)/d (glucose substrate) reported by other pilot-scale systems. Moreover, HPR was also greatly affected by pH. At an optimal pH of 5.5, the bacterial community became simple, while the efficient hydrogen producer Clostridium pasteurianum was dominant. The factors of energy output compared with the energy input (E(f)) ranged from 13.65 to 28.68 on biohydrogen, which is higher than the E(f) value on corn ethanol, biodiesel and sugarcane ethanol but in the similar range of cellulosic ethanol. Copyright (C) 2010, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.