Alumina doped alginate gel as cell carrier in ethanol fermentation process

Abstract

Alumina (Al₂O₃) doped alginate gel (AEC) was developed as a new type of cell carrier ethanol fermentation using flocculating yeast strain Saccharomyces cerevisiae M30. Sugar cane molasses was used as a carbon and energy source for fermentation medium at the initaial sugar concentration of 220 g/l. The performance of AEC carrier in ethanol fermentation was evaluated and compared to the conventional Ca-alginate bead (EC) and suspended cell (SC) in shaking flask at 10 rpm and 33℃, for 72 hours. The AEC arrier was sound to be more effective for yeast immobilization resulting in higher ethanol production, better porous struture and better mechanical properties in terms of tensile strength and percentage of elongation at break than the EC carrier. The addition of Al₂O₃ particle in the carrier could support cell activities and construct the network of cell and Al₂O₃ inside the gel bead. This network was able to create microporous structure that could improve mass transportation. To increase the efficiency of AEC carrier, the effets of bead diameter size, Na-alginate concentration and Al₂O₃ concentration on the ethanol fermentaton were investigated. The final ethanol concentraton was almost constant at 88-92 g/l under the range of 2-6 mm bead diameter. The maximum ethanol concentration was obtained when 2.5% (w/v) of Na-alginate and 5.0% (w/v of alginate) of Al₂O₃ were applied. Furthermor, the ethanol fermentation potential of the system applied with the convenient form of square sja[e AEC carroer )20 x 20 x 4 x mm³ ) was promising with its ethanol concentration comparable to that of the system of spherical shape ( 6 mm) AEC carrier. The continuous ethanol fermentation in packed bed reactor using the square shape AEC carrier worked efficiently and was stable over a period of 30 days. The maximum ethanol productivity of 12.34 g/l' or about 9 times of that of the batch system was achieved at the dilution rate of 0.28 h-1 Therefore, the AEC carrier was suitable for cell immobilization in ethanol fermentation process and successfully applied in packed bed reactor. The developed carrier had many advantages including high ethanol production, good mehanical property, stability and high immobilization yield.