Improving biomethane yield by controlling fermentation type of acidogenic phase in two-phase anaerobic co-digestion of food waste and rice straw

Controlling conditions to obtain different acidogenic fermentation types in a two-phase anaerobic co-digestion were investigated for improving the bio-methane yield from food waste (FW) and rice straw (RS). The results showed that the fermentation type in the acidogenic phase could be transformed by changing oxidation-reduction potential (ORP), pH, and organic loading rate (OLR). Three kinds of fermentation types were observed in acidogenic phase. Ethanol-type fermentation occurred at pH < 4.5 and ORP < −120 mV. Butyric acid-type fermentation appeared in the condition of pH > 5.0 with lower ORP and OLR ⩽ 6 g VS/L d. Mixed type fermentation was found in the transformation between butyric acid-type fermentation and ethanol-type fermentation. Among three fermentation types, the butyric-type fermentation achieved the highest acidification degree of 36%, biomethane yield of 535 mL CH4/g VS, and biodegradability of 95%. The finding indicated that controlling fermentation type of acidogenic phase could be one of effective method for achieving high biomethane production.