Conventional clarifiers are typically center-fed, with vertical inlet pipe discharging mixed liquor horizontally into a cylindrical bottomless well from which is the liquid distributed by ports or other structures into the clarifier. Though some arrangements are claimed to be superior to others, in real life the difference in performance is not dramatic. Principle difference, however, is between shallow and deep inlets. On the other hand, clarifiers with shallow inlets are rather resistant to short peak flows.
Deep inlets introduce the mixed liquor into the sludge blanket which is in consequence fluidized.
There are many old shallow final clarifiers in Europe and elsewhere. During plant extensions they have been in many cases supplemented by new, deeper clarifiers. A sensible use of the old ones is to load them moderately and by approximately constant flow and convert them to deep inlet. It is completely wrong to admit peak flows which shallow clarifiers with deep inlet do not tolerate. New deeper clarifier can process the variable additional flow.