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[Display omitted] • 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. In this study, exogenous Megasphaera elsdenii inoculum and acetate supplementation were introduced at the acidogenic phase to regulate the acidogenic fermentation pathway and assess their effects on food waste (FW) carbon conversion in two-phase anaerobic digestion (AD) system. These two additives significantly accelerated organic removal efficiency and subsequently increased FW hydrolysis and acidogenesis by 16% and 35%, respectively. As expected, two exogenous additives promoted butyrate fermentation during FW acidogenesis. With regard to the role of exogenous additives, both hydrogen and butyrate yields increased by over 60%. This desired increment resulted in a 25% increase in methane production. The overall carbon conversion from FW in the integrated two-phase AD system was enhanced by biochemical additives, which was 1.3-fold higher than that in control without any additives. Collectively, findings demonstrate the feasibility of regulating acidogenic fermentation via exogenous biochemical additives and its benefits on FW carbon conversion during AD process. [ABSTRACT FROM AUTHOR]