Fig. 4

Fed-batch fermentation by S912 in 5-L bioreactor. Growth (Gray triangle), consumed glucose (Blue square) and produced ethanol (Orange circle) in a sterilized biogas slurry medium at pH 6.0; b unsterilized biogas slurry medium at pH 3.8 are shown. Growth was determined by measuring OD₆₀₀ value. The biogas slurry used in sterilized fermentation was sterilized using a 0.22 μm filter membrane. The biogas slurry used in unsterilized fermentation was centrifuged at 4000 rpm and 4 °C, and collected supernatant. The biogas slurry mediums contain 100 g/L glucose and 1 g/L H₃PO₄. All fed-batch fermentations were carried out with 10% (v/v) inoculum cells at 30 °C without agitation. The working volume of fed-batch fermentation was 3 L, and the increasing of pH value was an indicator for replenishing with glucose until the final working volumes reached 4.0 L. All fed-batch fermentations were carried out in triplicate. Error bars show standard deviation (n = 3)