By comparing the average values of COD and BOD5 of this
experiment with EM addition and the average values of without
EM addition which were 28 and 15 for COD and BOD,
respectively, it was found that EM decreased both COD and
BOD5 concentrations in supernatant due to the activation of
microorganisms that were added to the system which consumed carbon source from bulk liquid.
COD uptake in
the anaerobic zone is usually due to PHA storage by polyphosphate
accumulating organisms (PAOs) or glycogen accumulating
organisms (GAOs).
As shown in Fig. 8 the average volatile fatty acid value
(VFA) before anaerobic tank (thickener) during 1st stage
was 164 mg/l with maximum and minimum values of 184
and 146 mg/l, respectively while the average VFA in thickener
supernatant at the same stage was 0.07 mg/l with maximum
and minimum values of 0.12 and 0.02 mg/l, respectively.