3.3. Semi-continuous fermentation studies for enhanced ethanol production by the selected mixed culture TERI SA1
3.3.1. Cell growth and pH profiles
Cell mass concentrations of mixed culture TERI SA1 increased during the first 144 h (Fig. 3a). However, cells were in the lag phase in the first 24 h. After 24 h cells entered the exponential phase and there was increase in cell mass concentration until 144 h. In addition, cells entered the stationary phase after 144 h. The maximum
cell mass concentration of 0.2 g L_1 was observed at 144 h. Minor changes in cell mass concentrations were observed during the stationary phase until 216 h. The pH of the culture media decreased during cell growth due to the production of acetic acid (Fig. 3a). The pH decreased from 6.0 to 4.6 until 192 h, at which time the acetic acid concentrations in medium reached a maximum (Fig. 3a). Subsequently, a minor change in pH was observed after
192 h.