In this paper are presented the results of the investigation on optimal process operational conditions of thermophilic dark fermentation and anaerobic digestion of food waste, testing a long-term run, applying an organic loading rate of 16.3 kgTVS/m(3)d in the first phase and 4.8 kgTVS/m(3)d in the second phase. The hydraulic retention times (HRTs) were maintained at 3.3 days and 12.6 days, respectively, for the first and second phase. Recirculation of anaerobic digested sludge, after a mild solid separation, was applied to the dark fermentation reactor in order to control the pH in the optimal hydrogen production range of 5-6. It was confirmed the possibility to obtain a stable hydrogen production, without using external chemicals for pH control, in a long-term test, with a specific hydrogen production of 66.7 1 per kg of total volatile solid (TVS) fed and a specific biogas production in the second phase of 0.72 m(3) per kgTVS fed; the produced biogas presented a typical composition with a stable presence of hydrogen and methane in the biogas mixture around 6 and 58%, respectively, carbon dioxide being the rest. Copyright (c) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.