Crude glycerol as sole carbon source
The type and concentration of carbon source is usually a key
factor affecting fermentation kinetics. In this experiment, the crude
glycerol concentration was 80 g/L, and peptone was chosen as thenitrogen source at a concentration of 0.3 g/L, which were the optimal
levels for fumaric acid fermentation by a series of optimization
experiments (data not shown). As was shown in Fig. 4, the concentration
of fumaric acid was found to increase in the course of time,
and maximum concentration of 4.37 g/L was achieved at 192 h,
with a low productivity of 0.023 g/L/h. There was much residual
glycerol when the fermentation was finished. As was previously
reported, in some biological conversion processes, impurities in
crude glycerol might influence the conversion of glycerol and cause
lower production rates and yields, compared to pure glycerol
under the same culture conditions (Liu et al., 2013b). Hence, fermentations
of pure glycerol were carried out under the same condition
to investigate the effect of impurities in crude glycerol on
fumaric acid production