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IS 7232:1974 is the Indian Standard (BIS) for method for imhoff cone test. 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).
! 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.
Standard Methods for the Examination of Water and Wastewater: 2540 F — Settleable Solids
Defines the standard procedure for determining settleable solids in water and wastewater using an Imhoff cone.
DIN 38409-9:1986DIN (Deutsches Institut für Normung), Germany
HighCurrent
German standard methods for the examination of water, waste water and sludge; general measures of effects and substances (group H); determination of settleable matter (H 9)
Specifies the German national method for determining settleable matter, which is functionally identical to the Imhoff cone test.
AS 3550.8-1991Standards Australia, Australia
HighWithdrawn
Waters — Determination of settleable matter — Imhoff cone method
Provided the Australian standard method for determining settleable matter with an Imhoff cone before harmonization.
Key Differences
≠International standards like SMEWW 2540 F specify correcting the final reading by estimating and subtracting the volume of any entrapped liquid pockets within the settled sludge, a detail not explicitly mentioned in IS 7232.
≠SMEWW 2540 F allows for the use of Imhoff cones made of clear plastic as an alternative to glass, whereas IS 7232:1974 explicitly specifies 'clear and transparent glass' as the material.
≠While IS 7232 specifies a single 60-minute procedure, SMEWW 2540 F also describes a shorter, 10-minute settling test variant for routine plant control to quickly observe settling characteristics.
≠IS 7232 provides specific manufacturing dimensional tolerances for the cone within the standard (e.g., total length 450 ± 10 mm), while international methods typically just reference a 'standard Imhoff cone', leaving dimensional specifications to glassware standards like DIN 12672.
Key Similarities
≈The fundamental principle of the test is identical: gravimetric settling of solids from a 1-litre sample in a calibrated conical vessel over a defined period.
≈All standards specify the use of a 1000 ml (1-litre) Imhoff cone as the primary apparatus for the test.
≈The total standard settling time is consistently 60 minutes (1 hour) across IS 7232 and its primary international equivalents.
≈A key procedural step, the intermediate agitation of the sample at 45 minutes to dislodge solids from the cone walls, is a common requirement in both IS 7232 and SMEWW 2540 F.
Parameter Comparison
Parameter
IS Value
International
Source
Apparatus Volume
1000 ml
1 L (1000 mL)
SMEWW 2540 F
Total Settling Time
60 minutes
1 hour (60 minutes)
SMEWW 2540 F
Intermediate Stirring Point
After 45 minutes
After 45 minutes
SMEWW 2540 F
Cone Material
Clear and transparent glass
Glass or suitable clear plastic
SMEWW 2540 F
Graduation (0 to 2 ml)
0.1 ml divisions
0.1 mL divisions
DIN 12672 (Glassware standard for Imhoff cones)
Graduation (2 to 10 ml)
0.5 ml divisions
0.5 mL divisions
DIN 12672
Reporting Units
ml/l
mL/L
SMEWW 2540 F
Top Internal Diameter Tolerance
105 ± 5 mm
100 to 106 mm (No explicit tolerance in method, based on DIN 12672)
DIN 12672
⚠ Verify details from original standards before use
Key Values4
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)
Tables & Referenced Sections
Key Tables
No tables data
Key Clauses
Clause 1 - Scope
Clause 3 - Apparatus
Clause 4 - Procedure
Clause 5 - Calculation and Reporting of Results
Frequently Asked Questions4
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).