A number of solids in the water have filterable or non-filterable properties. Non-filtered solids are called suspended solids.

The precipitated solids observed in water and wastewater are solids that accumulate spontaneously by the effect of their weight. The rate of collapse of these substances may vary depending on their size and density. The determination of solids that can collapse is of great importance for environmental engineers in the surface waters and domestic and industrial wastewaters. In general, the amounts of solids that can collapse are measured by volume and expressed in milligrams per liter.

Authorized laboratories use Imhoff cones to determine the amount of solids that can collapse. The water sample to be analyzed is mixed well and taken to the Imhoff cone and allowed to settle for about 45 minutes. At the end of the time, the substances adhering to the edges of the cone are mixed slowly and allowed to settle for an additional 15 minutes. The volume of the collapsible portion is then measured. If the result is taken in milligrams per liter, the suspended solids concentration of the sample is measured.

The concentration of precipitated solids is generally calculated using the following formula: Precipitable solid = Total suspended solids - Non-precipitated solids. In this formula, the values ​​are in milligrams per liter.

Contaminated waters, which contain high concentrations of solids, have adverse effects on the wastewater quality of industrial plants and the environment. In order to decide whether pre-settling tanks are required during the treatment of industrial wastewater and to what extent they will be used, whether the solids concentration exceeds a certain limit value. Because if the amount of solids that can collapse is above the limits, this water causes sedimentation in natural environment and formation of excess sludge.

Therefore, the determination of collapsible solids is an important issue and these measurements are also made by authorized laboratories within the scope of water and wastewater measurements.