Understanding Turbidity Measurement

Turbidity is a measure of the cloudiness or haziness of water or other liquids caused by large numbers of individual particles that are too small to be seen without magnification, but large enough to cause light scattering. Measuring turbidity is a key test of water quality.

Various methods and scales have been used throughout history to measure turbidity. These methods often rely on comparing the sample's turbidity to a set of standards.

Turbidity Measurement Scales and Units

Different scales and units exist for measuring turbidity, reflecting the evolution of measurement techniques:

• Jackson Turbidity Units (JTU): This was an early method based on measuring the depth of water at which a flame image viewed through the water sample disappears. This method used known concentrations of silica as standards to calibrate the measurement. This historical method is directly linked to the concept of a "Standard Silica Scale".
• Nephelometric Turbidity Units (NTU): This is the most common unit used today. It is based on measuring the light scattered by particles in the water sample at a 90-degree angle. Modern NTU measurements use Formazin polymer suspensions as the primary calibration standard, as they are more reproducible than silica standards. However, the underlying principle of a 'standard scale' using a reference material remains.
• Formazin Turbidity Units (FTU): Similar to NTU, also based on Formazin standards. Sometimes used interchangeably with NTU, though specific method variations can exist.
• Nephelometric Ratio Units (NRU): A variation that measures scattered light at multiple angles.

Considering the options provided, the question asks about a scale on which turbidity is measured. While modern methods primarily use Formazin standards for NTU, the historical basis for turbidity measurement scales, particularly related to the JTU method, involved the use of silica standards. The term "Standard silica scale" specifically refers to this historical approach where turbidity was quantified by comparing it to standards prepared from known amounts of finely divided silica.

Let's look at the other options:

• Platinum scale: This is not a scale typically used for turbidity. Platinum-Cobalt scale is a standard scale used for measuring the color of water.
• Silica cobalt scale: This term is not a recognized standard scale for either turbidity or color measurement. It seems to combine elements from different scales.
• Silica platinum scale: Similarly, this is not a recognized standard scale for water quality parameters like turbidity or color.
• Standard silica scale: As discussed, this relates directly to the historical method of turbidity measurement using silica standards to define turbidity units like JTU. Although superseded by Formazin standards for NTU/FTU, it represents a fundamental 'scale' used for turbidity measurement.

Therefore, among the given options, the Standard silica scale is the scale historically associated with the measurement of turbidity.

Revision Table: Water Quality Scales

Additional Information on Turbidity and Measurement

Turbidity is caused by the presence of suspended solids such as clay, silt, fine inorganic and organic matter, plankton, and other microscopic organisms. High turbidity can protect microorganisms from disinfection, interfere with filtration processes, and affect aquatic life by reducing light penetration.

Modern turbidity measurement uses instruments called turbidimeters or nephelometers. These instruments pass a beam of light through the water sample and measure the amount of light scattered or absorbed by the particles. Nephelometric turbidimeters, which measure scattered light at 90 degrees, are commonly used and report results in NTU.

Understanding the different scales and units used for water quality parameters like turbidity and color is important for interpreting laboratory results and ensuring water meets regulatory standards.