Influence of bioaugmentation with Acidipropionibacterium acidipropionici on propionate production and selectivity in different process configuration

Propionate concentration and selectivity from food waste fermentation appeared to be higher using the lactate route in a two-stage fermentation strategy (Bourgeois et al., 2027) than with direct food waste conversion leading to a mixture of VFAs (Bourgeois et al., 2025). However, in two-stage fermentation, it was not possible to distinguish the influence of lactate presence from the composition and concentration of the microbial community that develops during the first fermentation phase. Indeed, the initial inoculum (compost leachate or activated sludge) appeared to affect the performance of lactic fermentation more significantly, which consequently had an impact on propionic fermentation. Conversely, the development of the microbial community originating from different inocula could influence propionate production independently of the lactate concentration. Furthermore, given that the success of bioaugmentation with Acidipropionibacterium acidipropionici depends on the microbial interactions with the indigenous community, different behaviours may be observed during bioaugmentation in different communities. In addition, the initial proportion of the external strain relative to the total bacterial community governs its implementation and could change the metabolite production (Zheng et al., 2022a). This study therefore aims to evaluate targeted bioaugmentation with A. acidipropionici across two process configurations: a single-stage configuration, where food waste is directly fermented to propionate, and a two-stage configuration, where food waste first undergoes a lactic fermentation, generating a lactate-enriched effluent feeding the subsequent propionate stage. The lactic stage is seeded with different inoculum sources (CL or AS), investigating whether the microbial community established by each inoculum source influences the efficacy of the subsequent bioaugmentation step.