A pilot-scale two-phase hydrogen/methane fermentation system generated 3.9 L biogas per unit time and reactor volume from food waste, of which the fraction of H(2) was approximately 60% at a hydraulic retention time (HRT) of 21 h. As substrate, 90% of the carbohydrates in the organic compounds were consumed, based on COD removal efficiency, and the hydrogen yield was approximately 1.82 (H(2)-mol/glucose-mol). The maximum decomposition rate coefficient of hydrogen fermentation was observed at an HRT of 21 h, indicating that reducing HRTs improves hydrogen production. Over 80% of the methane was produced in the methane fermentation tank and the predominant fraction of organic acids after methane fermentation comprised acetic acid. Based on our economic evaluation, two-phase hydrogen/methane fermentation has greater potential for recovering energy than methane-only fermentation. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.