The production of H-2 from food residues and manure has been optimised using a central composite face-centred (CCF) design. In all 17 assays were run, varying the temperature (20, 37 and 55 degrees C), hydraulic retention time (2, S and 8 days) and N-2-flow rates (5, 25 or 125 mL/min). Completely stirred tank reactors (2 L) were operated for three hydraulic retention times and hydrogen production was determined during the course of a 24-h period before termination. The concentrations of H-2, CH4 and volatile fatty acids were measured, together with pH, throughout the experiment. A temperature of 55 degrees C, combined with a sparging rate of 125 mL/min, and a hydraulic retention time of 2 days resulted in the highest hydrogen formation. The maximal production experimentally obtained was 16.5mLH(2)/gVS. A model was calculated from the data with a squared correlation coefficient (R-2) of 0.97 and a predictive power of 0.64 (Q(2)). (C) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.