Medium Optimization for Mixed Alcohols Production by Glycerol Utilizing Immobilized Clostridium pasteurianum MTCC 116

S. Khanna, A. Ranjan, A. Goyal and V. S. Moholkar

Abstract
Glycerol, a major byproduct of biodiesel production may be utilized by a variety of microorganisms for production of value added products. The production of bioalcohols from anaerobic fermentation of glycerol depends greatly on the composition of the medium. Therefore, optimization of media components holds great significance for achieving higher product yield. The media components for production of mixed alcohols by Clostridium pasteurianum immobilized on silica was optimized by Taguchi statistical method in shake flasks. After initial screening using the one-factor-at-a-time approach, a total of 6 media components, KH2PO4–K2HPO4, yeast extract, MgSO4 · 7H2O, CaCl2 · 2H2O, FeSO4 · 7H2O, (NH4)2SO4 each at two different concentrations were employed for optimization experiment (L8 array). The composition of optimized medium was KH2PO4–K2HPO4 2 g L–1, yeast extract 5 g L–1, MgSO4 · 7H2O 0.1 g L–1 and (NH4)2SO4 0.1 g L–1. Analysis of Variance (ANOVA) of the optimized factors gave a model F, p and R2 values of 2003.76, <0.001 and 99.7 respectively. The predicted total product concentration with optimized media was 17.51 g L–1. Fermentation with optimized medium was carried out in a stirred tank bioreactor. The total alcohol production in bioreactor after 10 days of fermentation was 17.67 g L–1 at 37 ºC, 25 g L–1 carbon source and 3 % w/v support with immobilized cells, which was higher than the value predicted by the model. Hence, Taguchi design of experiment helped in determining the appropriate medium composition for obtaining optimum mixed alcohols yield.

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Keywords
Medium optimization, Taguchi method, bioreactor, Clostridium pasteurianum, immobilization