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The measurement of turbidity is a key test of both water clarity and water quality. [citation needed] There are two standard units for reporting turbidity: Formazin Nephelometric Units (FNU) from ISO 7027 and Nephelometric Turbidity Units (NTU) from USEPA Method 180.1.
Three glass vials used as turbidity standards for 5, 50, and 500 nephelometric turbidity units (NTU). Turbidity is a measure of the cloudiness of water based on light scattering by particles at a 90-degree angle to the detector. A turbidity sensor is placed in water with a light source and a detector at a 90-degree angle to one another.
The unit is called Formazin Turbidity Unit (FTU). Nephelometric Turbidity Units (NTU) specified by United States Environmental Protection Agency is a special case of FTU, where a white light source and certain geometrical properties of the measurement apparatus are specified. (Sometimes the alternate form "nephelos turbidity units" is used [7] [8])
Nephelometric Turbidity Unit, a measure of the cloudiness of a liquid; Nevada–Texas–Utah Retort, a shale oil extraction technology; New Threat Upgrade, a US Navy anti-air warfare ships system upgrade; NTU method uses the Number of Transfer Units to calculate the effectiveness of a heat exchanger
For turbidity measurement, a formazine suspension is prepared by mixing solutions of 10 g/L hydrazine sulfate and 100 g/L hexamethylenetetramine with ultrapure water. [5] The resulting solution is left for 48 hours, at 25 °C ±1 °C, for the suspension to develop. This produces a suspension with a turbidity value of 4000 NTU/FAU/FTU/FNU. This ...
[2]: 89–98 Turbidity is a measure of the light scattering ability of suspended matter in the water. [2]: 131–137 Salinity measures water density or conductivity changes caused by dissolved materials. [2]: 99–100
Different kinds of Secchi disks. A marine style on the left and the freshwater version on the right. The Secchi depth is reached when the reflectance equals the intensity of light backscattered from the water. 1.7 divided into this depth in metres yields an attenuation coefficient (also called an extinction coefficient), for the available light averaged over the Secchi disk depth.
In the studies conducted in 1991 on the quality of the water stored in the two surface reservoirs it was concluded that the water stored had high turbidity values (about 1 NTU which was more than the standard acceptable value of 0.5 NTU) as it received surface water inflows from the catchment of the reservoir.