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

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.

为应对能源危机，乙醇重新成为石油基液体燃料的替代品或掺混增效剂。采用固定化细胞载体的连续发酵工艺具备诸多优势，包括更高的转化率、相对简便的产物分离流程、生物催化剂可重复利用以及较高的生产效率。因此，本研究针对以丝瓜络增强海藻酸盐包埋固定化酿酒酵母（Saccharomyces cerevisiae M30）的方式开展连续乙醇发酵展开探究。为对比9×9×3 mm³与20×20×3 mm³两种规格的海藻酸盐-丝瓜络载体的生产效率，本实验以初始糖浓度220 g/L的培养基，在500 mL锥形瓶中开展批式发酵，振荡频率设为150 rpm，反应温度控制为33 ℃。实验结果表明，载体尺寸变化对细胞活性无显著影响。本研究随后在填充床反应器中开展连续乙醇发酵实验，设置的初始糖浓度梯度为202、222及248 g/L，稀释率梯度为0.11、0.16、0.20及0.30 h⁻¹，反应温度维持在32±1 ℃。当初始糖浓度为222 g/L、稀释率为0.16 h⁻¹时，发酵生产效率达到最优值10.57 g/(L·h)，此时乙醇浓度为66.06 g/L。当初始糖浓度为222 g/L、稀释率为0.11 h⁻¹时，可获得最高乙醇浓度81.29 g/L。实验结果证实，海藻酸盐-丝瓜络基质可成功作为细胞载体应用于填充床柱式连续乙醇发酵体系。该自制载体具备优异的机械性能与发达的多孔结构，可实现长达30天的稳定运行与高效乙醇生产。基于本研究结果，建议后续开展更大规模的相关研究，以推动该工艺的工业化应用优化。