Ethanol production by alginate immobilised yeast in a fluidised bed bioreactor

Abstract

Yeast, immobilised in alginate beads of known standard size and mechanical strength, has been utilised in a novel design of fluidised bed bioreactor which avoids problems of particle flotation and gas logging. Circulating substrate simultaneously entered the top and bottom of the bed. The bioreactor operated reliably for periods of up to 20 days. Increasing alginate concentration in the range 1–5% (w/w) had little effect on the performance of the immobilised yeast in converting ethanol to glucose but reduced the tendency of beads to split. Increasing bead diameter in the range 1–5 mm increased the tendency to split and reduced overall conversion of glucose. A model was developed to describe the consumption of glucose within beads based on Michaelis–Menten kinetics and the diffusion of glucose into beads. Application of the model to experimental results showed maximum reaction velocity to be independent of bead diameter and alginate concentration. The model confirmed that the observed reduction in ethanol yield compared with free yeast cells was caused by the lower substrate concentration towards the centre of the bead as opposed to any change in the metabolic rate of the immobilised cells.

Texture analysis of TEM micrographs of alginate gels for cell microencapsulation

“…Among them all, alginate is certainly the most widely used material. The most promising applications of alginate gels are in the field of cell microencapsulation (Donati and Paoletti, 2009), as in (micro) bio-reactors for the production of chemicals (Gilson and Thomas, 1995) and high-added value bio-chemicals, or as encapsulation matrices in tissue engineering, with adult (Kinasiewicz et al, 2008;Siebers et al, 1997) and stem cells (Maguire et al, 2007).…”

Ethanol fermentation of a diluted molasses medium by Saccharomyces cerevisiae immobilized on chrysotile

“…However, 30% of the industries have substituted batch by continuous fermentation processes (Wheals et al, 1999) because this presented several advantages. To improve the productivity and ethanol yield and to avoid the utilization of centrifuges that are expensive, continuous processes with immobilized cells in different carriers as glass, synthetic polymers as polyacrylamide (Lida, 1993) and polypropilene gels (Inloes et al, 1983), calcium alginate (Bravo and Gonzales, 1991;Gilson and Thomas, 1995;Roukas, 1994;Sanches et al, 1996), kissiris (Argiriou et al, 1996) have been suggested, although some carriers presented difficulties at industrial scale. For example, alginate beads that can be destroyed due to friction and CO 2 evolution inside the beads (Gilson and Thomas, 1995).…”

Performance evaluation for Bioethanol production in three reactors: Batch, packed bed and Fluidized bed bio-reactors

“…(Sitton and Gaddy (1980)). Conversions in fluidized bed reactors were better than batch reactor (Gilson and Thomas (1995) (Najafpour, et al (2004)). Figure 7,8 show the similar behavior of 4% sodium alginate made beads shown better performance than 2% and 6% sodium alginate beads for packed and fluidized bed bio-reactors.…”