On the other hand, pH decreased in the process of food
waste anaerobic fermentation (Chen et al., 2015). Therefore, when
initial inoculum density increased to 200 and 250 mg L1, both of
COD removal efficiencies reduced to about 36%, probably because
the low pH could inhibit the activity of hydrolytic anaerobic bacteria
when the pH of acidogenic phase was down to ‘‘over-acid
ification” (Li and Ren, 1998).