Monday, April 30, 2007

Modeling and simulation of a continuous process for ethanol production by fermentation using immobilized Saccharomyces cerevisiae in a fluidized bed bioreactor

Giovanilton Ferreira Silva1, Andrea Lopes de Oliveira Ferreira2, and Luciana R. B. Goncalves2. (1) Tecnologias Bioenergéticas – TECBIO, R. Rômulo Proença, S/N – Campus do Pici, NUTEC, PAR-TEC, Bloco A, – Galpão 01, Fortaleza, Brazil, (2) Chemical Engineering, Universidade Federal do Ceará, Campus do Pici, Bloco 709, Fortaleza, Brazil

The objective of this work was to investigate a new route for ethanol production using a continuous Fluidized Bed Bioreactor with Saccharomyces cerevisiae immobilized in Ca-alginate gel beads. A heterogeneous model describing the fermentation process has been proposed. Glucose utilization, ethanol production and growth pattern of yeast cells, immobilized in calcium alginate gel beads, using four different initial substrate concentrations (20, 40, 80 and 100gdm 3) were studied. In the model, biomass and product formations were based on the Monod equation where the specific production rates depend on the concentration of the limiting substrate, glucose, and on some parameters such as saturation constant and specific rate constants. These substrate utilization and growth reactions were incorporated into mass balances for a completely mixed, fluidized bed bioreactor, resulting in a series of coupled ordinary differential equations and the resulting model equations were solved numerically. The fluidized-bed bioreactor considered in this investigation is composed of two phases: a fluid phase comprised mainly of the substrate (glucose) and the product (ethanol); and a solid phase which is the biocatalyst. The following assumptions were employed in the model: (1) the system is isothermal and (2) the fluid phase back-mixing can be quantified by an axial dispersion coefficient. The effects of some operating and design parameters on the performance of the fluidized-bed bioreactor were also analyzed.