pH-controlled batch reactor fermentation
In the batch reactor, fermentation of wood
hydrolyzate (batch IV) was studied in pH-controlled
conditions. The pH range of 5.6±6.4 was obtained by
addition of potassium hydroxide. Recycled cells and
reduced nutrient supplementation with zinc were used in
the fermentation medium. The growth of C. shehatae
FPL-Y-049 did not start until 24 h had passed as a result
of adaptation to high acetate content of the hydrolyzate
(Parekh et al., 1986). At pH 5.7, ethanol concentration
was 20 g/l but ethanol yield was 0.38 (Fig. 4). The lower
ethanol concentration could be attributed to either
ethanol respiration or low levels of inhibition as a consequence
of potassium acetate formation in the medium
during buffering to maintain pH of fermentation. Xylitol
(5±7 g/l) accumulated in the reactor as well as low levels
of glycerol.