Comparative analysis of ethanolic fermentation in two continuous flocculation bioreactors and effect of flocculation additive

Applications of yeast flocculation in biotechnological processes

“…The use of a fluidised bed for flocculating cultures is not advisable, either, as the density difference between flocs and medium is rather small and fluidisation would be achieved at very low air/liquid flow rates, enhancing the mass transfer limitations already existing. On the contrary, bubble columns and airlift reactors (especially the later) are being extensively used with three-phase systems in processes involving flocculating organisms [60,118,[122][123][124][125][126][127][128][129].…”

“…A maximum ethanol outlet concentration of 44.8 g/L and a maximum ethanol productivity of 24.4 g ⋅ L -1 ⋅ h -1 were obtained. Considering the need to develop new and simpler fermentation systems and the suitability of the airlift bioreactor for cultures using flocculating microorganisms, a 5.4 L internal loop airlift bioreactor was tested and compared with the previous system [126] using a highly flocculating strain of S. cerevisiae growing on glucose. A comparison was made in terms of start-up evolution, overall performance and power costs.…”

“…Thus, a reduction in floc size could be expected to bring a reduction in mass transfer limitations, leading to an increase of productivity. Vicente et al [155] introduced static mixers in the draught tube of the internal loop airlift bioreactor used by Sousa et al [126,127], achieving an effective reduction of the floc size (3 mm to 1 mm in diameter). Steady state data at different dilution rates were measured for both systems (the original and the modified bioreactor) and the results were compared in terms of specific consumption/production rates and ethanol productivity.…”

Modelling diffusion-reaction phenomena in yeast flocs of Saccharomyces cerevisiae

“…In order to achieve such objectives, techniques such as the use of high cell density systems have been thoroughly studied [1±5]. Among these, the use of occulent micro-organisms cultivated in bioreactors where their sedimentation characteristics can be exploited is a very promising area, having low associated costs and design simplicity as main advantages [6,7].…”

“…In fact, reductions in diffusional limitations have been reported [6,7,20,21], suggesting an increase of the effective diffusion coef®cient of the substrates in the¯oc when some¯occulating additives are used.…”