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.