Question

Mention the various units for measurement of turbidity

Answer 1

NTU stands for Nephelometric Turbidity Unit and signifies that the instrument is measuring scattered light from the sample at a 90-degree angle from the incident light. 
FNU stands for Formazin Nephelometric Units and also signifies that the instrument is measuring scattered light from the sample at a 90-degree angle from the incident light. FNU is most often used when referencing the ISO 7027 (European) turbidity method. 
NTU is most often used when referencing the USEPA Method 180.1 or Standard Methods For the Examination of Water and Wastewater.  
When formazin was initially adopted as the primary reference standard for turbidity, units of FTU or Formazin Turbidity Units were used. These units, however, do not specify how the instrument measures the sample. 

FAU or Formazin Attenuation Units signify that the instrument is measuring the decrease in transmitted light through the sample at an angle of 180 degrees to the incident light. This type of measurement is often made in a spectrophotometer or colorimeter and is not considered a valid turbidity measurement by most regulatory agencies. 

 A JTU or Jackson Turbidity Unit is a historical unit used when measurements were made visually using a Jackson Candle Turbidimeter. Water was poured into a tube until a flame underneath the tube could no longer be distinguished. 

The turbidity units NTU, FNU, FTU, AND FAU are all based on calibrations using the same formazin primary standards. Therefore when a formazin standard is measured, the value for each of these units will be the same, however the value on samples may differ significantly.

Answer 2

Answer:

NTU, FNU, FTU, FAU, and JTU turbidity units

Explanation -

Turbidity is a measure of a liquid's relative transparency. It is a water optical characteristic that measures the amount of light scattered by material in the water when a light is flashed through a sample of water.

• NTU denotes that the equipment is measuring scattered light from the sample at a 90-degree angle from the incident light.
• FNU is an abbreviation for Formazin Nephelometric Units, and it also means that the equipment is measuring scattered light from the sample at a 90-degree angle from the source light. The most common abbreviation is FNU.
• Units of FTU, or Formazin Turbidity Units, were employed when formazin was first designated as the principal reference standard for turbidity. However, these units do not define how the instrument measures the sample.
• FAU, or Formazin Attenuation Units, indicate that the equipment is measuring the reduction in transmitted light through the sample at a 180-degree angle to the incoming light. Most regulatory authorities do not consider this sort of turbidity measurement to be legitimate since it is commonly performed using a spectrophotometer or colourimeter.
• JTU, or Jackson Turbidity Unit, is a historical unit used when visual measurements were taken using a Jackson Candle Turbidimeter. Water was poured into a tube until the flame underneath it could no longer be seen.