Harnessing Packed-Bed Bioreactors’ Potential in Solid-State Fermentation: The Case of Beauveria bassiana Conidia Production

The packed-bed bioreactor is among the most promising reactor configurations for solid-state fermentation. However, the bed thickness poses several limitations involving mass and energy transfer, heat generation, and the homogeneity of the material, hampering its development at the industrial scale. Fungi are among the most promising microorganisms used in this configuration; however, only polypropylene bags and trays are used at the industrial scale. In this work, Beauveria bassiana is used to demonstrate the potential of solid-state fermentation for conidia production. A scale-up from 0.5 L to 22 L is presented, starting with substrate selection, optimization via design of experiments and 22 L batches. The optimized parameters were 70% moisture, 6.5 × 106 conidia mL−1 inoculum concentration, 20 mL min−1 airflow, 25 °C; temperature, and 40 C/N ratio. After optimization, beer draff was chosen as the preferred substrate for scale-up. Air-filled porosity was found to be the key parameter in fungal solid-state fermentation scale-up, establishing values of around 80% as necessary for fungal conidia production when working in a 22 L packed-bed bioreactor. When compared with the tray bioreactor, the packed bed obtained higher conidia production due to its better use of the total reactor volume. Our study harnesses the potential of the packed-bed bioreactor and serves as a base for further scale-up to industrial scale.