The combination of substrate materials and bacteria is an important factor affecting conversion technology for biological hydrogen production. We performed anaerobic hydrogen fermentation of apple pomace wastes using rhizosphere bacterial microflora of rice as the parent inoculum. In the vial test, the optimal condition for hydrogen fermentation was initial pH 6.0, 35 degrees C, and 73.4 g pomace per liter of medium (equivalent to 10 g-hexose/L). In the batch experiment (pH 6.0, temperature 35 degrees C) the hydrogen yield reached 2.3 mol-H(2)/mol-hexose. The time course of biogas production and PCR-DGGE analysis suggest that Clostridium spp. decomposed degradable carbohydrates rapidly and a part of the refractory carbohydrate (e.g. pectin) gradually in the apple pomace slurry. In addition to hydrogen, volatile fatty acids (VFAs) were produced in the anaerobic fermentation of apple pomace, which can be a substrate for methane fermentation. The rice rhizosphere can be a promising source of inoculum bacteria for hydrogen fermentation in combination with plant material waste like apple pomace. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.