Hydrogen Production from Food Waste by Integrated Dark Fermentation, Anaerobic Digestion and Biogas Reforming: An Electron-Resolved Model

Integrated dark fermentation (DF), anaerobic digestion (AD), and biogas reforming have been proposed for converting food waste to hydrogen and are usually assessed by yield. This study proves that total hydrogen is fixed by the chemical oxygen demand (COD) of the feed minus losses to biomass, residue, and oxidation, so metabolic route and reformer configuration act only through these losses, and that oxygen feed lowers the reformer ceiling to 4 − 2nO2 mol H2 per mol CH4. A process model enforcing carbon and COD balances, with Gibbs-equilibrium reforming and all process fuel inside the control volume, quantified them. Across eight reformer configurations, yield varied by 20.6% and specific energy by 62.0%. On a carbohydrate basis, adding DF before AD raised yield by 17.4% and lowered specific energy by 26.1%; for a three-fraction food-waste composition, by 5.3% and 9.8%. Over 200 parameter draws, four configurations maximised yield, none in over 38.5%; one minimised specific energy in 86.5%. These frequencies depend on the declared ranges and equilibrium reforming; at 15 bar the yield winner remained split, although the yield and energy optima coincided. Hydrogen yield should be constrained rather than optimised, because its ranking of designs is not identifiable at present.