3.2. COD removal performance
The influent and effluent CODtot, CODdis, CODdis/CODtot
and the achieved accumulated removal efficiencies of the
three reactors during each operation phase are presented
in Table 2 and Figure 2. The average CODtot and CODdis
concentration in the different compartment of the three reactors
during each operation phase are given in Table 3. The
organic loading rate (OLR) in the three operation phases
varied because different amounts of primary sludge were
added to keep a constant TS value. Note that the removal
efficiencies of CODtot and CODdis in all the three reactors
increased with the increase in the operation time. This is