The Imhoff tank digestion chamber should have a volume of ___ to __ cubic feet per capita.

• A. 2.0-3.0
• B. 3.0-3.5
• C. 3.5-4.0
• D. 4.0-4.5

Answer: (C)

Imhoff tank digestion chamber is sized to give enough space for the digestion and storage of solids produced by each person served. The recommended volume is about 3.5 to 4.0 cubic feet per person because this range provides sufficient residence time for the solids to digest and stabilize before leaving the chamber, without making the tank unnecessarily large. If the per-person capacity is too low, digestion may be incomplete and sludge could accumulate or pass on; if it’s too high, the tank becomes larger and more expensive than needed. To size the chamber for a given population, multiply the per-person volume by the number of people served. That’s why the 3.5–4.0 cubic feet per person range is the best fit.