What is ntu in turbidity?

NTU stands for turbidimetric turbidity unit, which is the unit used to measure the turbidity of a fluid or the presence of suspended particles in water. The higher the concentration of suspended matter in water, the dirtier it looks and the higher the turbidity.

NTU units are most commonly used in water purification plants. We prefer to use suspended solids (SS) measured in mg/l or ppm because we operate primarily in the wastewater treatment plant market, but there is a relationship between suspended solids and NTU.

The relationship between NTU and suspended solids is as follows: 1 mg/l (ppm) is equivalent to 3 NTU. for example, 300 mg/l (ppm) of SS is 900 NTU.

Different turbidity of water
Different turbidity of water

According to the World Health Organization, the turbidity of drinking water should not exceed 5 NTU.

What is the difference between turbidity units NTU, FNU, FTU, JTU and FAU?

NTU stands for Turbidimetric Turbidity Units and indicates that the instrument is measuring the scattered light of the sample at an angle of 90 degrees to the incident light.

FNU stands for Formazin Nephelometric Units and also indicates that the instrument is measuring scattered light from a sample at an angle of 90 degrees to the incident light. fnu is most commonly used in reference to ISO 7027 (European) turbidity method.

NTU is most commonly used in reference to USEPA Method 180.1 or the standard method for water and wastewater examination.
When formalin was originally adopted as the primary reference standard for turbidity, FTU units or formalin turbidity units were used. However, these units do not specify how the instrument measures the sample.

JTU or Jackson turbidity units are the historical units used when measurements were made visually using a Jackson candle turbidimeter. Pour water into the test tube until the flame is no longer visible below the test tube.

FAU or Formazin attenuation units indicate that the instrument is measuring the reduction of transmitted light in a sample at an angle of 180 degrees to the incident light. This type of measurement is typically performed in a spectrophotometer or colorimeter and is not considered a valid turbidity measurement by most regulatory agencies.

The turbidity units NTU, FNU, FTU and FAU are based on calibrations using the same formazin primary standards. Therefore, when measuring the formazin standards, the values will be the same for each unit, but the values on the samples may vary significantly.