Display omitted •A pilot-scale process of VFA production from FW was established under acid condition.•The highest VFA production yield was 0.79 mgCOD/mgCOD at pH of 6.5.•Higher pH resulted in an increase in the proportion of butyric acid.•Dominant microbial function group promoted the conversion of acetic to butyric acid. Here, a pilot-scale volatile fatty acids (VFAs) production system was established using food waste (FW) as feedstock under acidic conditions. The effects of pH (uncontrolled, 4.5, 5.5, and 6.5) on the FW acidification system were investigated. The results showed that VFAs concentration increased from 8419 to 15048 mg COD/L with pH level increasing from 4.5 to 6.5, and the highest VFA production yield (0.79 mgCOD/mgCOD) was obtained at a pH of 6.5. A larger proportion of butyric acid (52.9%) was observed, accompanied by a 23% decrease of acetic acid when pH was elevated to 6.5. Microbial analysis showed that Clostridium sensu stricto 1, Sporanaerobacter, and Proteiniphilum were dominant, which not only positively influence the hydrolysis and acidogenesis processes but also play an essential role in the conversion of acetic acid to butyric acid. In summary, this study provides a valuable reference for large-scale FW treatment to recover valuable resources.