In stage 1, the pH in the CSTR reactor was controlled between
4.0 ± 0.1 by the pH controller lasting for 24 days. As shown in
Fig. 1 , the total COD concentration of fermentation products
increased gradually from start-up to 7th day and then maintained
relatively stable around 23.5 ± 2.5 gCOD/L till the end of stage 1. In
the stable period, lactic acid, acetate and ethanol were the three
main products. In addition, lactic acid was produced with high
amount of 10–20 g/L. Obviously, the concentration of lactic acid
from the 16th day to 23th day was lower than the concentration
from the 7th day to 15th day, however, for ethanol it was exactly
on the contrary. Therefore, the whole operational time was sepa-rated into three phases: phase 1 (1–7 day), phase 2 (7–15 day),
phase 3(16–24 day).