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Turbidity Measurement

Turbidity Measurement for Quality Assurance - Procedures and Applications from Water to Wine

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Measure turbidity


Turbidity is a subjective perception and shows other than electrochemical or physical parameters variable effects. It is based on moving, uneven sized and formed particles dispersed in a solution. Turbidity measurement serves as indicator and quality parameter  in many applications.

  • Turbidity particles in drinking water serve as indicator, e.g. for potential  bacterial growth or pond overuse.
  • Turbidity measurement online devices  in sewage plant outlets are installed for quality control of cleaning performance, residual load of undissolved substances and indication of malfunctions in the process.
  • In industrial applications turbidity measurement is used as quality indicator for production or raw material (food & beverage, motor development..) and can reach up to 10.000 NTU/FNU.

There are distinct measurement procedures with Infrared- and Tungsten light sources

  • Nephelometric measurement at 90°
  • Transmission measurement at  180°, e.g. also photometrically
  • Ratio measurement as combination of various angles (for high turbidity values, application or manufacturer specific optics)

All procedures are detecting the change of light intensity when passing a sample. This is caused by absorption and straylight effects of the particles. The calibration of instruments is performed with primary or secondary standards (Formazine, polymer solutions) , which are simulating a real-world particle distribution.

In drinking water,  turbidity is determined by nephelometric straylight procedure. This procedure is standardized  by DIN EN ISO 7027 with IR light source and unit FNU (Formazine Nephelometric Unit); US EPA 180.1 requires tungsten light and the unit NTU (Nephelometric Turbidity Unit). 1 NTU = 1 FNU. 

For turbidity measurements Online-, lab and portable instruments as well as turbidity sensors are in use.

Schematic illustration of detection procedures used in turbidity measurement: nephelometric 90° scattered light, 180° transmission or Ratio measurement comibing various angles
WTW - Measure Turbidity

Stationary Meters for Waste Water and more

  • Wastewater treatment plants
  • Drinking water plants
  • Industrial applications

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