2.3. Culture media
The composition of culture medium contained the following components: 10 0 g/L glucose, 10 g/L yeast extract, 1 g/L KH2 PO4 ,1 g/L (NH4 )2 SO4 and 0.5 g/L MgSO4 ·7H2 O [15]. In addition, in order to examine the effects of metal ions on the ethanol production, the appropriate test solution of sulfate salts and hydroxide(FeSO4 ·7H2 O, MgSO4 ·7H2 O, CaSO4 ·2H2 O and Al(OH)3 ) were added to the culture medium.