Instruction Manual TN-100/ T-100
19
8. Addendum 1: Turbidity
8.1 Definition
Turbidity is defined as an “expression of the optical property that causes light to be
scattered and absorbed rather than transmitted in straight lines through the
sample.”
1
That is, turbidity is the measure of relative sample clarity, not colour.
Water with cloudy or opaque appearance will have high turbidity, while water that is
clear or translucent will have low turbidity. High turbidity value is caused by particles
such as slit, clay, microorganisms, and organic matter. By definition, turbidity is not
a direct measure of these particles but rather a measure of how these particles
scatter light.
8.2 Why Is It Important?
For drinking water application, a turbidity value may give an indication of presence
of bacteria, pathogens, or particles that can shelter harmful organisms from
disinfection process. Therefore, turbidity measurement is particularly useful for
water treatment plants to ensure cleanliness.
In industrial processes, turbidity can be part of quality control measure to ensure
efficiency in treatment or manufacturing process.
8.3 Measurement Principle
There are two internationally accepted standard specifications for turbidity
measurement. These are the international standard ISO 7027 and the US EPA
method 180.1.
Basically the ISO 7027 is a more stringent standard and requires the use of a
monochromatic light source. It also governs the design of a turbidimeter in the
following areas: (1) Light source’s wavelength; (2) Light sources’ spectral
bandwidth; (3) Measuring angle; (4) Aperture angle in water sample; (5) Distance
traversed by incident light and scattered light within the sample; (6) Calibration
standard.
The TN-100/ T-100 turbidimeter follows the ISO 7027 standard whose specification
allows for greater reproducibility of the measured values and greater agreement
between other measuring instruments.
1
Provided by “Standard Methods for the Examination of Water and Wastewater, APHA, AWWA
and WPCF, 16
th
Edition, 1985.
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