Continuous succinic acid production by immobilized cells of Actinobacillus succinogenes in a fluidized bed reactor: Entrapment in alginate beads

The production of succinic acid (SA) was investigated by using immobilized cultures of Actinobacillus succinogenes in alginate beads. Immobilized cell cultures operated in batch mode were tested by varying the initial glucose concentration between 20 and 80 g/L and the bead concentration (mass of beads per liter of fermentation broth) between 50 and 250 g/L. Free cells fermentation tests were also carried out to compare the performances of free cells vs. immobilized cells. The best results were obtained with immobilized cells at initial glucose concentration of 60 g/L and 250 g/L of beads: the final SA concentration was 69 ± 0.2 g/L and the SA yield was 1.15 ± 0.02 g/g. Repeated batch fermentation tests were performed to assess the mechanical stability of the alginate beads. The continuous fermentation process was investigated in a three-phase fluidized bed reactor (FBR) using cell entrapped in alginate beads (the solid phase). The process performances were studied and described as acid production (succinic acid included) and sugar conversion. The performances of the FBR were particularly attractive because it was possible to combine high SA productivity (35.6 g/Lh) with high SA concentration (31 g/L) and substrate conversion (76.4 %).