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Imhoff Settling Cone


    The Imhoff Settling Cone & Rack is used to determine the volume of settleable solids from a known volume of waste. The sample may be fresh or saline water, or domestic or industrial wastewater. The settleable solids test is a useful method for determining the amount of solid entering a wastewater treatment plant, as well as for estimating the amount of sludge to be expected during the treatment process. In addition, the Imhoff cone can be used to measure the volume of sand in a sample of well water.

The total volume of solids in an aqueous sample is a combination of suspended and dissolved matter. The Imhoff Settling Cone measures only the volume of suspended solids in a sample in mL/L. Suspended solids can be problematic for stream health and aquatic life because they block out sunlight, which reduces the amount of photosynthesis that can occur. This in turn reduces the amount of dissolved oxygen in the water column, limiting the organisms that can live there. Increased suspended solids can also increase the water temperature because the solids absorb heat from the sun. Suspended solids reduce visibility of the aquatic life affecting their ability to feed. It can also clog fish gills and smother fish eggs and aquatic larvae. Suspended solids can include but are not limited to silt and clay particles, decaying plant and animal matter, industrial waste and sewage.

Requirements: The test method requires that the sample be left undisturbed for at least 1 hour. Therefore, samples can be taken out in the field, and then tested back in the classroom or laboratory.

Suggested Grade Levels: 8th and above
Suggested Courses: Earth Science, Environmental Science
Video Demonstration: (None available at this time)


The following directions describe the standard test method for using an Imhoff cone to measure settleable solids. In addition to supplied equipment you will need a timer or clock and glass stirring rod or spoon.

  1. Mix the water sample well. Pour 1 liter of the water sample into a cone. Place the cone in the rack.
  2. Set a timer for 45 minutes. After 45 minutes gently run the glass stirring rod along the edges of the cone to loosen material that might be stuck on the sides of the cone.

  3. Allow to settle for 15 more minutes. Measure the volume of settleable solids by reading the height of the solids using the scale on the side of the cone.

  4. Record your data as milliliter per Liter (ml/L).

  5. Notice that the cone is fully graduated from the vortex upward.
    1. 0-1 mL in 0.1 mL
    2. 1-10 mL in 0.5 mL
    3. 10-20 mL in 1 mL
    4. 20-40 mL in 2 mL
    5. 40-100 mL in 10 mL
    6. 100-500 mL in 50 mL
    7. 500-1000 mL in 100 mL.
      The screw closure allows user to read graudations to zero and the plug allows removal of the sediment.
SAGE Bristol,
Feb 7, 2012, 8:48 AM