Because the water contains suspended and colloidal particles, the original colorless and transparent water has a turbidity phenomenon, and the degree of turbidity is called turbidity. The unit of turbidity is expressed by “degree”, which is equivalent to 1mg of SiO2 in 1L of water, the degree of turbidity is 1 degree, or Jackson. The unit of turbidity is JTU, 1JTU = 1mg / L of white clay suspension.
The turbidity displayed by modern instruments is the unit of scattered turbidity NTU, also known as TU. 1TU = 1JTU. Recently, it is internationally believed that the turbidity standard prepared with urotropine-hydrazine sulfate has good reproducibility, and it has been selected as the national standard FTU. 1FTU = 1JTU.
Turbidity is an optical effect, and the degree to which light is blocked when passing through the water layer indicates the ability of the water layer to scatter and absorb light. It is not only related to the content of suspended matter, but also related to the composition of the impurities in the water, particle size, shape and the reflective properties of its surface.
Controlling turbidity is an important content of industrial water treatment and an important indicator of water quality. According to the different uses of water, there are different requirements for turbidity. The turbidity of domestic drinking water should not exceed 5 degrees; the turbidity of supplementary water required for circulating cooling water treatment is 2 to 5 degrees; the influent (raw water) of desalination The turbidity should be less than 3 degrees; the manufacture of man-made fibers requires that the turbidity of water be less than 0.3 degrees. Since the suspended and colloidal particles that make up turbidity are generally stable and mostly have a negative charge, they will not settle without chemical treatment. In industrial water treatment, coagulation, clarification and filtration are mainly used to reduce water turbidity.