Strategies for reducing solvent toxicity in extractive ethanol fermentation

Abstract

Extractive fermentation is a widely preferred technique in which the products of fermentation are removed from the fermentation medium by a proper solvent, in order to avoid the inhibitory effects of the products. In this work, decanol, which has a high distribution coefficient with respect to the biocompatible solvents, was used in extractive ethanol fermentation. In order to reduce decanol toxicity, Saccharomyces cerevisiae cells were immobilized in calcium alginate gel. Further, sunflower oil and Al2O3 were added to the immobilization media. Experiments were performed in 250-mL Erlenmeyer flasks that were placed in the constant-temperature bath of a constant stirring-rate shaker. Ethanol concentrations were measured to observe the effect of various parameters on ethanol production. Immobilization media included 10, 20, and 30% sunflower oil, or 5, 10, and 20% Al2O3, or Al2O3 and sunflower oil together. The ratio of the volume of aqueous phase to that of decanol phase ranged from 2:1 to 6:1. It was observed that protection depends on the oil, Al2O3, and decanol amounts. Utilization of sunflower oil (30%) and Al2O3 (5%) together yielded best results.