obtained in color removal. The decolorization efficiencies
decreased to 80 and 78 from 90% at low SRT values. The
optimum SRT value for COD and color was determined to
be 11 days in aerobic reactor (Fig. 9). At higher loading rates
and low SRT values both MLSS and SVI values decreased
because of washout of microorganisms from the effluent of
the aerobic reactor (MLSS = 2000–2300 mg l−1 and SVI =
100–120 mg l−1). Increases in MLSS and SVI values were
observed at high SRT values (MLSS = 2900–4000 mg l−1
and SVI = 200–220 mg l−1). A decrease in MLSS concentrations
was observed at high organic loadings even were
studied at high SRT values due to washout of biomass in effluent.
This caused poor settling properties in CSTR reactor,
which is associated with low COD removal efficiencies in
aerobic reactor. In general, high COD removal efficiencies
Fig. 10. The effects of dye loading on color removal efficiencies in anaerobic anaerobic/aerobic sequential system.
in aerobic reactor can be accomplished by low F/M ratios at
low organic loadings resulting with active microorganisms
at high concentration (See Figs. 8 and 9).