3.5. Effect of various metal ion concentrations on ethanol
production
Figs. 4–7 show the effects of various metal ion concentrations
on ethanol production and residual glucose after 24 h of incubation
at initial glucose concentration of 100 g/L. When the concentration
of 0.2 g/L of Fe2+ was added to the culture broth (Fig. 4), the
highest ethanol concentration obtained was 48.8 g/L, being the
same value as the control. In case of the addition of 0.4 g/L of
Fe2+, the ethanol production was significantly reduced to 4.3 g/L
and the ethanol could not be produced at the concentration of
0.6 g/L Fe2+ and above. The addition of 1 g/L of Ca2+ and 4 g/L
of Mg2+ slightly inhibited the ethanol production by Z. mobilis
(Figs. 5 and 6). The more each ion concentrations were increased,
the more inhibition behavior of ethanol production was observed.
On the other hand, the addition of Al3+ at the concentrations from
1 to 20 g/L had no inhibitory effect on the conversion of glucose
to ethanol (Fig. 7). The results indicate that Fe2+ and Ca2+ have
a significant inhibitory effect on growth of Z. mobilis at an initial
paper sludge concentration of 200 g/L.