An experimental study on fermentative H2 production from food waste as affected by pH

• The effect of pH on fermentative hydrogen production from food waste was investigated.
• Batch tests were conducted on mixtures of food waste and wastewater activated sludge.
• Under optimized conditions, the process was able to produce ∼120 Nl H2/kg VS.
• Metabolites production was monitored to study the prevalent metabolic pathways.
• Mixed acetate/butyrate and alcoholic-type fermentations were the main metabolic pathways.

Batch dark fermentation experiments were performed on food waste and mixtures of food waste and wastewater activated sludge to evaluate the influence of pH on biological H2 production and compare the process performance with and without inoculum addition. The effect of a preliminary thermal shock treatment of the inoculum was also investigated as a means to harvest the hydrogenogenic biomass. The best performance in terms of both H2 generation potential and process kinetics was observed at pH = 6.5 under all experimental conditions (no inoculum, and untreated or thermally treated inoculum added). H2 production from food waste was found to be feasible even without inoculum addition, although thermal pre-treatment of the inoculum notably increased the maximum production and reduced the lag phase duration. The analysis of the fermentation products indicated that the biological hydrogen production could be mainly ascribed to a mixed acetate/butyrate-type fermentation. However, the presence of additional metabolites in the digestate, including propionate and ethanol, also indicated that other metabolic pathways were active during the process, reducing substrate conversion into hydrogen. The plateau in H2 generation was found to mirror the condition at which soluble carbohydrates were depleted. Beyond this condition, homoacetogenesis probably started to play a role in the degradation process.