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Definition
Why s t
mportant?
Measurement
Principle
Thermo Scientific Orion AQUAfast AQ3010 Turbidity Meter User Guide
Turbidity Theory
Appendix 1
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 . " That is, turbidity is the measure of relative sample
clarity, not color .
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 silt, 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 .
For drinking water applications, 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 . For
wastewater effluent testing, turbidity is often required to ensure that the
released effluent will not harm the environment .
In industrial processes, turbidity can be part of quality control measure to
ensure efficiency in treatment or manufacturing process .
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 turbidity
meter 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 and (6) Calibration standard .
The AQ3010 turbidity meter follows the ISO 7027 standard whose
specification allows for greater reproducibility of the measured values and
greater agreement between other measuring instruments .
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