What is the minimum distance, in inches, that the sludge level in the Imhoff digester should be below the slot opening?

• A. 18
• B. 12
• C. 24
• D. 30

Answer: (A)

In an Imhoff digester, maintaining a clear separation between the sludge blanket and the outlet is essential. The slot opening is where the clarified liquid exits, so the sludge level must stay well below it to prevent solids from being drawn into the effluent or causing blockages. Keeping the sludge at least eighteen inches below the slot opening provides enough liquid head and a stable interface for the digestion process, reducing the chance of solids escaping with the effluent and helping maintain proper digestion and settling.

So, the minimum distance is eighteen inches.