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organics. This creates the problem of the deficiency of electron donor for the
conversion of nitrate to nitrogen at the denitrification stage.
Aeration basin
BOD removal
&
nitrification
Carbon source
Anoxic basin
Denitrification
................................................. .'
a) Two-sludge or separate stage system
Anoxic basin
Denitrification
b) Single-sludge system
Aeration basin
BOD removal
&
nitrification
Mixed Liquer Recycle
Aeration basin
BOD removal
&
nitrification
Anoxic basin
Endogenous Denitrification
Clarifier
Clarifier
Clarifier
'0 ••••••••••••••• _ ••••••••••••••••••••••••••••• __ ••••••• _ ••••• _ •••••••••• _ •••••••••••••••••••••••••••••••••• _ •• .'
c) Endogenous nitrification-denitrification system
Fig. I. Conventional systems for biological wastewater treatment including nitrogen
removal