Comparison of bio-hydrogen and bio-methane production performance in continuous two-phase anaerobic fermentation system between co-digestion and digestate recirculation

The effect of co-digestion of food waste (FW) and cow dung (CD) with different ratios, and digestate recirculation with different recirculation ratios (RR) on the substrate degradation and energy production in continuous two stage anaerobic fermentation system was investigated. Results from experiments indicated that co-digestion and digestate recirculation could promote the hydrogen production rate (HPR) and the methane production rate (MPR). Maximum HPR and MPR of 3.3 and 3.1 L/L/d were achieved for two-stage fermentation with recirculation system at RR of 0.4. Meanwhile, both co-digestion and digestate recirculation technology could reduce the amount of alkali addition to maintain pH in the hydrogen-reactor. Compared to digestate recirculation, co digestion of FW and CD promote much more energy production, 654.9 and 4854.8 kJ/kgVSr were obtained from the co-digestion of FW and CD with the ratio of 2:1 in the hydrogen reactor and the methane reactor.