Regulation of acidogenic fermentation through exogenous additives for promoting carbon conversion of food waste in two-phase anaerobic system

•The effect of specific inoculation and acetate supplement in LBR-UASB was studied.•Exogenous additives improved FW hydrolysis and lactate–butyrate conversion in LBR.•The increase in methane yield relied on the enhancement of butyrate fermentation.•Carbon conversion efficiency in this two-phase AD increased by 33% with additives.