What is the purpose of the Imhoff cone test?

To volumetrically measure the amount of settleable solids in a 1-litre sample of water or wastewater over a 1-hour period (Clause 1).

What is the standard settling time for the test?

The sample is settled for 45 minutes, stirred gently, and then settled for another 15 minutes, for a total standard settling time of 1 hour (Clause 4.1).

How much sample volume is used?

The test uses a 1-litre (1000 ml) sample, which fills the Imhoff cone to its top graduation mark (Clause 4.1).

How are the results of the Imhoff cone test reported?

The results are reported as millilitres of settleable solids per litre (ml/l), which is the direct reading from the cone's graduations (Clause 5.1).

IS 7232

: 1974

Method for Imhoff cone test

CurrentSpecializedTesting MethodEnvironmental · Public Health Engineering

Download PDF BIS Portal Google

This standard specifies the method for determining the volume of settleable solids in water and wastewater using an Imhoff cone. It details the required apparatus, the step-by-step procedure including settling times, and the method for reporting the results in millilitres per litre (ml/l).

Method for Imhoff cone test

Quick Reference Values

Standard test sample volume1000 ml

Standard total settling period1 hour

Primary settling period before stirring45 minutes

Reporting unitml/l

Key Formulas

Result (ml/l) = Volume of settled solids read from cone (ml)

Practical Notes

Ensure the inner walls of the cone are perfectly clean and not greasy to prevent solids from adhering to the sides, which would lead to inaccurate readings.

Pour the sample into the cone slowly and gently to avoid breaking up the flocs, which can alter the settling characteristics and final volume.

After the initial 45-minute settling period, gently stir the sides with a rod to dislodge any settled material adhering to the cone walls.