Application of gravitational sedimentation to efficient cellular recycling in continuous alcoholic fermentation

Abstract

A mathematical model for the sedimentation velocity in an inclined parallel plate sedimenter is proposed. The parameters of the alcoholic fermentation broth (cell density of Saccharomyces cerevisiae, density of the fermentation medium, viscosity of the broth at various alcohol and biomass contents) were determined experimentally. The sedimentation velocities were predicted under the various operational conditions and parameters, both of the broth (the alcohol concentration and cell content) and the sedimenter prototype (length, distance between the plates, and slope). The proposed model for the sedimentation velocity presented a good correlation with the experimental results of continuous sedimentation. These sedimenter prototypes were assembled and tested for efficiency of separation of yeast cell under conditions considered for interest for continuous alcoholic fermentation. A selective filter for the overflow composed of calcium alginate gel improved operation. A high operational stability, high separation efficiency (over 98%), and adequate settler residence times (about 20 min) were attained. The operational results permitted the operation of continuous alcoholic fermentation with cellular recycling effected exclusively by gravitational sedimentation, this characterizing a process of enormous industrial interest because of the operational simplicity and low operational and maintenance costs.

Potential of cell retention techniques for large‐scale high‐density perfusion culture of suspended mammalian cells

“…Settlers were reviewed earlier and compared with filters and centrifuges as retention devices for animal cell perfusion cultures (Tokashiki and Takamatsu, 1993). They were also used for other biological systems like yeast and plant cells (Maia and Nelson, 1993;Su et al, 1996). Numerous designs were investigated: (1) single inclined plate (Batt et al, 1990;Searles et al, 1994;Lassen and Emborg, 1994), (2) multiple inclined plates (Knaack et al, 1994;Thompson and Wilson, 1994;Stevens et al, 1994), (3) vertical settling zone (Hülscher et al, 1992;Arai et al, 1993;Wen et al, 2000), (4) or horizontal settling zone (Wen et al, 2000).…”

A simple apparatus for measuring cell settling velocity

“…Gravity settlers have been successfully applied as cell retention devices in perfusion cell cultures from the bench‐top to large scale industrial applications 1–10. The capacity of an inclined gravity settler to clarify cell suspension is described in Eq.…”

A Semi-Empirical Approach to Estimate Kinetic Parameters for the Batch and Continuous Settling of Flocculating Yeast Slurries

“…It is generally accepted that a high concentration of yeast favors an increased ethanol yield of the fermentation process [2]. Several techniques that promote the accumulation of biomass in fermenters have been used in continuous fermentation processes, including cell immobilization in polymeric matrices and cell recycle by centrifugation or filtration through membranes [2][3][4]. Good performances have been reported for processes using immobilized cells [2]; however, procedures and materials involved in this technique are inaccessible to a large number of small industrial units [3].…”

“…Several techniques that promote the accumulation of biomass in fermenters have been used in continuous fermentation processes, including cell immobilization in polymeric matrices and cell recycle by centrifugation or filtration through membranes [2][3][4]. Good performances have been reported for processes using immobilized cells [2]; however, procedures and materials involved in this technique are inaccessible to a large number of small industrial units [3]. Centrifugation and filtration equipments are extremely expensive and prone to mechanical problems; the use of these equipments is limited due to high investment and maintenance costs [2,5,6].…”

“…These flocculating strains present much higher settling velocities than those of individual cells and hence can be efficiently separated even by small devices [11]. Moreover, when scaling-up of the separation process is taken into account, sedimentation might be more feasible than other techniques due to its simplicity and operational stability as well as low cost and adequacy for any production scale [3].…”