Ethanol fermentation of sweet sorghum stalk juice by immobilized yeast

The relationship between the Brix and the total soluble sugar content of sweet sorghum stalk juice was determined through one-dimensional linear regression. Meanwhile, ethanol fermentation experiments were conducted in a shaking flask and a 10 L fluidized bed bioreactor with stalk juice of SNTZ No.2 sweet sorghum variety when immobilized yeast was applied. The experimental results in the shaking flask showed that the influence sequence to improve ethanol yield was (NH₄)₂SO₄, MgSO₄, K₂HPO₄, and the optimum ratios of K₂HPO₄, (NH₄)₂SO₄ and MgSO₄ were 0.125%, 0.200% and 0.050%, respectively. Ethanol yields with inorganic salts were increased by 4.0%～8.0% compared to without one. K₂HPO₄ and (NH₄)₂SO₄ were greatly significant to the experiment results, and MgSO₄ ranked second. The experimental results in the fluidized bed bioreactor showed that ethanol yields were nearly equal to four kinds of ideal inorganic salts. And the ethanol yields with inorganic salts were higher than that without one. It was beneficial for ethanol production when blending ratios of K₂HPO₄, (NH₄)₂SO₄ and MgSO₄ were 0.125%, 0.200% and 0.010%, respectively from the aspect of reducing cost. The research provides a scientific basis for fuel ethanol development.