of sCOD/tCOD was 80.0%, which was obviously higher than 68.6%
when in stage 1 with pH controlled at 4.0. It indicated that the
hydrolysis reaction was obviously improved with the increase of
pH from 4.0 to 5.0. Bouallagui et al. (2004) also reported that the
optimal pH for better hydrolytic bacteria activity was between
5.0 and 6.0. The average concentration of total COD of individual
fermentation product was 29.5 gCOD/L and thus the ratio of
tCODp/sCOD was 84.5%, which was almost same with the ratio of
84.1% in stage 1. Therefore, the improvement of lactic acid fermen-tation was mainly because of the enhancement of hydrolysis
reaction