Continuous ethanol fermentation was performed in a tower- shaped reactor with a working volume of 450 mL, as previously described (Tang et al., 2006). Before fermentation, the reactor was sterilized by circulating 2 mg/L of NaClO solution overnight, and then sterilized tap water was supplied continuously for 1 day. Approximately 450 mL of pre-cultivated broth (containing 1.5 × 108 cells/mL) was inoculated into the reactor, and then sweet sorghum juice was fed into the reactor at a dilution rate of 0.15 h−1. Before feeding sweet sorghum juice into the reactor, the total sugar content (the sum of the concentrations of glucose, fructose and sucrose) was adjusted to 150 g/L by adding sucrose (hereafter called the adjusted sweet sorghum juice, while the unadjusted material is called the raw sweet sorghum juice), based on the total sugar con- centration of 120–142 g/L reported by Andrzejewski et al. (2013a). In order to prevent the loss of sugar by bacterial contamination, the adjusted sweet sorghum juice was placed at 70 ◦C, based on the results of a preliminary study. The effects of supplementing the feedstock with mineral nutrients, dilution rate, temperature and aeration rate on continuous ethanol fermentation were inves- tigated. Ethanol yield was calculated as follow:
Continuous ethanol fermentation was performed in a tower- shaped reactor with a working volume of 450 mL, as previously described (Tang et al., 2006). Before fermentation, the reactor was sterilized by circulating 2 mg/L of NaClO solution overnight, and then sterilized tap water was supplied continuously for 1 day. Approximately 450 mL of pre-cultivated broth (containing 1.5 × 108 cells/mL) was inoculated into the reactor, and then sweet sorghum juice was fed into the reactor at a dilution rate of 0.15 h−1. Before feeding sweet sorghum juice into the reactor, the total sugar content (the sum of the concentrations of glucose, fructose and sucrose) was adjusted to 150 g/L by adding sucrose (hereafter called the adjusted sweet sorghum juice, while the unadjusted material is called the raw sweet sorghum juice), based on the total sugar con- centration of 120–142 g/L reported by Andrzejewski et al. (2013a). In order to prevent the loss of sugar by bacterial contamination, the adjusted sweet sorghum juice was placed at 70 ◦C, based on the results of a preliminary study. The effects of supplementing the feedstock with mineral nutrients, dilution rate, temperature and aeration rate on continuous ethanol fermentation were inves- tigated. Ethanol yield was calculated as follow:
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