Determination of the Turbidity of Water-Environmental Engg Lab

Determination of the turbidity of water can be done by using turbidimeters, the turbidity test is the extent to which light is scattered or absorbed by suspended materials in water.

Absorption and scattering are influenced by both size and surface characteristics of the suspended matter.

Turbidity test is not a direct quantitative measurement of suspended solids. The most commonly used method for the measurement of turbidity by nephelometer method.The determination of turbidity of water can be found by this method.

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Principle of turbidity experiment

Turbidimeters with scattered light detectors located at 90 degrees to the incident beam are called nephelometers. This method is based on a comparison of the intensity of light scattered by the sample under defined conditions, with the intensity of light scattered by a standard reference suspension under same conditions.

Determination of the Turbidity of Water
Determination of the Turbidity of Water

The higher the intensity of scattered light, the higher will be the turbidity.The turbidity measurement by nephelometer requires formazine polymer.

Formazine Polymer is used as the primary standard reference suspension. Turbidity is measured in Nephelometric-Turbidity Units (NTU).

Requirements of turbidity experiment

  • Nephelometer, with a tungsten filament light source and a 90o detector system
  • Sample cells of quartz glass
  • Standard turbidity solution (Formazine Polymer solution of 40 NTU and 400 NTU)
  • Clean distilled water

 Turbidity test procedure

  1. Calibrate the nephelometer according to the instructions given in the manufacturer’s manual (Insert the turbidity-free distilled water and set the reading to zero. Insert 40 NTU standard and set reading to 40 and using 400 NTU solution set reading to 400. Repeat)
  2. Pour the well-mixed sample it into the cell and read the turbidity directly from the display
  3. If the turbidity of the sample exceeds 400 NTU, dilute the sample properly and fine turbidity again.
  4. Then, actual turbidity = observed turbidity X Dilution Factor
  5. The readings will get in terms of NTU units.

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The video below shows the video of turbidity experiment.

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