Which test uses the Imhoff cone?

• A. Settable solids test
• B. DO test
• C. BOD test
• D. Turbidity test

Answer: (A)

Measuring how much solids settle out of wastewater by gravity in a fixed time is the idea being tested. The Imhoff cone is designed for this purpose: you fill it with a sample, let the solids settle by gravity, and then read the volume of settled solids after a specified period (commonly about 60 minutes). This yields the amount of settleable solids, expressed as a volume per volume (for example, mL of settleable solids per liter of sample). The cone’s shape helps minimize disturbance and keeps the settled material from being resuspended, giving a direct reading of what portions of the solids would settle in a clarifier.

This is why the Imhoff cone is used in the settable solids test. Other tests mentioned don’t use this device: dissolved oxygen tests rely on oxygen measurements in water, BOD tests involve incubating samples in bottles to measure oxygen demand over time, and turbidity tests assess how much light is scattered by suspended particles using a turbidity instrument.