Standard Methods; 2540 A, 2540 F

The settleable solids test is the measurement of the volume of solids in one liter of sample that will settle to the bottom of an Imhoff cone during a specific time period. The test indicates the volume of solids removed by settling in sedimentation tanks, clarifiers or ponds. The settleable solids test indicates whether the primary and secondary processes are functioning properly.

• Imhoff cone
• Stirring rod
• Rack for holding Imhoff cone
• Timer

No reagents are needed for the settleable solids test.

Samples may be stored in a plastic or glass container and kept for 7 days at 4° C. See sample storage and preservation table.

The following must be recorded on the data sheet:

• Sample identification (source, name, and date(s) of collection)
• Analyst(s)
• Raw data / final results with correct units (reported to nearest mL/L). Clean samples such as the final effluent should have greater accuracy than samples from a clarifier.
• Description of unusual sample characteristics

The procedure for this test is very simple and does not lend itself to quality control requirements in the classical sense. The most important aspect is to ensure that the time requirements are closely followed. This is to standardize testing that will simulate the theoretical operation of the clarifier or settling basin.

1. Fill an Imhoff cone to the one-liter mark with a well mixed sample.
2. Allow sample to settle in the Imhoff cone for 45 minutes.
3. Gently stir the sample with a glass rod to release the suspended matter clinging to the sides of the Imhoff cone.
4. Let sample settle for an additional 15 minutes.
5. At this point, one hour has passed. Record the volume of settleable solids (in milliliters) in the Imhoff cone.

Note: Do not include any floating solids or any voids in the settled solids as settleable matter.

No calculations are necessary to determine the settleable solids. The data obtained after the one hour test is the result. Any calculations done with this result will be used to calculate efficiencies or determine whether the equipment is operating properly.

• Collect sample
• Prepare raw data sheet
• Add sample to Imhoff cone and allow to settle
• After 45 minutes, gently stir sample
• After an additional 15 minutes, record results