Conversion relationship between NTU and FTU turbidity

According to national standards, formaldehyde hydrazine is used as the sole turbidity standard solution, with NTU as the only unit for measuring turbidity. Due to different measurement methods, various units are used for representation. Strictly speaking, turbidity measured using a scattering light turbidimeter calibrated with a formazin turbidity standard solution can be expressed in NTU (short for Wephelomefric Turbidity Unit), whereas when a transmittance light turbidimeter is used, the value is expressed in FTU (Formazin Turbidity Unit). 1 JTU is essentially close to 1 NTU.

Due to the presence of suspended and colloidal particles in water, water that is originally colorless and transparent becomes turbid; the degree of this turbidity is referred to as turbidity. The unit for turbidity is expressed in degrees; it corresponds to a turbidity level of 1 degree, or Jackson, when 1 mg of SiO (or an equivalent amount of milligrams of kaolin or diatomite) is present in 1 liter of water. The unit of turbidity is JTU, with 1 JTU equal to 1 mg/L of white clay suspension. The turbidity displayed by modern instruments is expressed in the unit of scattered turbidity, NTU, also known as TU. 1TU = 1JTU. Recently, internationally it has been considered that a turbidity standard prepared using urotropine and hydrazine sulfate exhibits good reproducibility, and thus has been chosen as the unified FTU standard for various countries. 1FTU = 1JTU. Turbidity is an optical effect that represents the degree to which light is hindered as it passes through a water layer; it indicates the water layer’s ability to scatter and absorb light. It is related not only to the concentration of suspended solids, but also to the composition of impurities in the water, their particle size and shape, as well as the reflectivity of their surfaces. Controlling turbidity is an important aspect of industrial water treatment, and it is also a key water quality indicator.