Continuous ethanol production using immobilized yeast cells entrapped in loofa reinforced alginate carriers

Abstract

In response the energy crisis, ethanol has re-emerged as an alternative to, or extender for petroleum based liquid fuels. Continuous fermentation using immobilized cell carriers offers many advantages such as higher conversion, relative ease of product separation, reuse of biocatalyst and high productivity. Therefore, in this study continuous ethanol fermentation using immobilized yeast cells (Saccharomyces cerevisiae M30) entrapped in loofa reinforced alginate was investigated. To compare productivity of alginate-loofa at sizes of 9 x 9 x 3 mm[superscript 3] and 20 x 20 x 3 mm[superscript 3], the batch fermentation was carried out in 500 ml Erlenmeyer flask at shaking frequency of 150 rpm and temperature of 33 [degree Celcius] using initial sugar concentration of 220 g/l. It was found that there were no significant differences in cell activity regarding the change of the carrier size. The continuous ethanol fermentation was studied in packed-bed reactor with various initial sugar concentrations (202, 222 and 248 g/l) and dilution rates (0.11, 0.16, 0.20 and 0.30 h[superscript -1]) of 32 ± 1 [degree Celcius]. At 222 g/l of initial sugar concentration and 0.16 h[superscript -1] of the dilution rate, the optimum of productivity was obtained (10.57 g/l h) with the ethanol concentration of 66.06 g/l. The maximum of ethanol concentration (81.29 g/l) was obtained at 222 g/l of initial sugar concentration and 0.11 h[superscript -1] of the dilution rate. The experimental result revealed that the alginate-loofa matrix was successfully used as a cell carrier in packed bed column for continuous ethanol fermentation. With favorable mechanical properties and high porous structure of the developed carrier, a fairly stable operation and high ethanol production over the course of 30 days were achieved. Based on the results of this work, subsequent studies especially in larger scale is recommended to ameliorate for industrial production.