settleable

Settleable is an adjective used to describe materials that will settle out of a suspension under gravity within a defined period. In environmental science and engineering, settleable solids are the portion of suspended solids that can be removed by gravity in a sedimentation process, such as a clarifier or settling tank.

Measurement of settleability is commonly performed with a settling test. An Imhoff cone or graduated cylinder is filled with a sample and left undisturbed for a specified time, typically 60 minutes in standard tests. The volume or mass of solids that have settled to the bottom is then measured and reported as settleable solids, often expressed as liters of settled volume per liter of sample or as milligrams per liter. The test assesses how readily particles will separate from the liquid by gravity.

Settleability depends on particle size, density, shape, and interparticle forces, as well as conditions such as temperature, salinity, and viscosity. It is influenced by treatment steps like coagulation and flocculation, which can enhance the formation of larger, faster-settling aggregates.

In practice, settleability helps engineers design and evaluate wastewater treatment processes, primary clarifiers, and sludge management strategies. It distinguishes solids that settle readily from those that remain in suspension, guiding decisions about process configuration, residence times, and chemical dosing.

Related terms include sedimentation, turbidity, coagulation, and flocculation. The concept is commonly used in water and wastewater engineering, environmental science, and soil and sediment studies.