Biohydrogen production from food waste in batch and semi-continuous conditions: evaluation of a two-phase approach with digestate recirculation for pH control

The research investigated the production of Biohythane in a two-phase anaerobic digestion process treating food waste as substrate. Preliminary batch assays were carried out at initial organic loadings of 15, 20, 25 and 30 kg TVS m -3 , in stirred 1.5-l reactors at 55 °C. The results showed all hydrogen was produced within the first 24 hours after feeding and the highest load tested gave the maximum hydrogen production (0.047 m 3 H2 kg -1 VS, H2 30%). Similar loadings were then tested in a two-phase system. Hydraulic retention times of 3 and 12 days were applied to the first and second reactor respectively. In order to keep the pH at ~5.5, either supernatant or whole digestate from the methanogenic reactor was recirculated to the first phase. Results showed that hydrogen was produced (0.117 Nm 3 kg -1 VS, 47.7%) when recirculating whole digestate with an organic loading rate of 20 kg TVS m -3 day -1 .