drinking water

Drinking Water

Turbidity has long played a critical role in drinking water production with the most common application being as a regulatory compliance parameter in filter effluent ap­plications. More recently water treatment plants have discovered the benefits of mea­suring turbidity in other applications such as source water and backwash monitoring.

Turbidity Measurement Technologies

Turbidity is defined as an expression of the optical properties of a sample that causes light rays to be scattered and absorbed rather than be transmit­ted in straight lines through the sample. Turbidity is caused by the presence of suspended and dissolved matter such as clay, silt, finely divided organic matter, plankton, other microscopic organisms, organic acids, and dyes. It’s important to note that turbidity is not a measure of the quantity of suspended solids in a sample, but instead, an aggregate measure of the combined scattering effect of the water sample’s suspended material on an inci­dent light source.

Three types of light sources are com­monly used in turbidimeters: incandes­cent, light emitting diode (LED), and la­ser diodes. Incandescent light sources emit a broad spectrum of light that includes shorter wavelengths that are better suited to detection of smaller particles. Com­mon infrared LEDs (IR) used in turbidity measurements emit 830-890 nanometer (nm) light that is typically not absorbed by visible color in the sample, eliminating a common source of error. Laser-based light sources are very sensitive to small changes in turbidity and are often used to moni­tor the performance of filters producing ultrapure water such as is commonly used in many industrial processes.