It is well known that a stable pH value close to neutrality is
important for the formation of good-quality granulated sludge
[19,20]. The optimum pH ranges from 6.5 to 7.5 for the anaerobic
reactor because methanogens are extremely sensitive to pH.
VFA is an important intermediate of the anaerobic digestion process,
and methanogens primarily use VFA to form methane. The
accumulation of VFA in an anaerobic reactor can directly reflect the
inactivity of methanogens or deterioration of the operating conditions,
and higher VFA levels will inhibit methanogens. Therefore,
the VFA in effluent is considered an important indicator during
reactor operation