Effect of operating conditions on food waste fermentation to enhance VFA production and propionic acid selectivity

Food waste fermentation offers a promising approach for the production of volatile fatty acids (VFAs). However, controlling the VFA profile, particularly enriching propionic acid, remains a challenge due to the complexity of microbial communities involved. This study investigates the influence of key operating parameters—initial pH, temperature, and substrate concentration—on VFA production and microbial community dynamics. Batch fermentation experiments using reconstituted food waste were conducted under varying conditions. The highest propionic acid selectivity was achieved at an initial pH of 9, a temperature of 35 °C, and a substrate concentration of 7.8 g VS/L, with statistically significant improvement over other conditions. Microbial community analysis based on 16S rDNA sequencing revealed distinct profiles shaped by the operational settings. Notably, increased relative abundances of Enterobacteriaceae , Lachnospiraceae , and Exiguobacterium spp. were associated with higher propionic acid production. These results highlight the strong interplay between fermentation conditions, microbial ecology, and metabolite profiles, providing insights for optimising food waste valorisation towards selective VFA production. • Specific enrichment in propionic acid was observed at 35°C, pH 9 and FW=7.8 g VS/L • The composition of microbial communities was influenced by operating conditions • Correlations were established between metabolite profiles and microbial relative abundances • Propionic and valeric acids correlated with the Exiguobacterium genus