The relationship between turbidity and suspended solids
Turbidity: Turbidity is a physical indicator that measures the clarity of water. It mainly refers to the degree of scattering and absorption of light by suspended particles in the water. Suspended particles can include soil, silt, microorganisms, algae, and other organic and inorganic particles. Turbidity is usually measured using optical instruments, such as turbidimeters, which quantify turbidity by measuring the intensity of light scattered by particles in the water. The international unit of turbidity is usually NTU (nephelometric turbidity units, nephelometric refers to the scattered light measurement method) or FTU (formazine turbidity units, based on a specific standard solution as a reference).
Suspended Solids (SS): Suspended solids refer to solid particulate matter that cannot be separated through natural precipitation in water. They are suspended in water, insoluble in water, and have a density greater than water. There are various types of suspended matter, including inorganic matter (such as sediment, mineral particles), organic matter (such as humus, microorganisms) and various tiny particles. The measurement of suspended solids usually uses the filtration method, that is, a certain volume of water sample is filtered through a specific filter membrane, and then the residue on the filter membrane is dried and weighed, and the mass concentration of suspended solids is expressed in milligrams per liter (mg/L).
The relationship between turbidity and suspended solids: There is a certain correlation between turbidity and suspended solids concentration, but it is not a simple linear relationship. In the low turbidity range, turbidity is usually proportional to the mass concentration of suspended matter, since more suspended particles means stronger light scattering. However, as turbidity increases, especially when the concentration of suspended particles is too high or factors such as particle size, shape, refractive index, etc. change, the relationship between turbidity and suspended matter concentration becomes more complex and no longer remains strict. single value correspondence. In addition, turbidity does not reflect all types of suspended solids. For example, some particles with very small or extremely large diameters may not contribute much to turbidity, but are included in the total amount of suspended solids.
In practical applications, sometimes empirical formulas or calibration curves can be established based on experimental data of turbidity and suspended solids concentration under specific conditions to estimate suspended solids concentration using turbidity, but this is limited to approximate calculations under specific conditions and has limited accuracy. For accurate suspended solids concentration measurements, one still has to rely on gravimetric or other standardized chemical analysis methods.