Effects of temperature, hydraulic retention time and hydrogen extraction rate on hydrogen production from the fermentation of food industry residues and manure

The production of H2 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∘C), hydraulic retention time (2, 5 and 8 days) and N2-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 H2, CH4 and volatile fatty acids were measured, together with pH, throughout the experiment. A temperature of 55∘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 16.5 mL H2/g VS. A model was calculated from the data with a squared correlation coefficient (R2)(R2) of 0.97 and a predictive power of 0.64 (Q2)(Q2).