Sedimentation
- Slovak term: Slovenský termín
- Process by which suspended solids denser than water settle as sludge (WHO 1992).
- Treatment process using gravity to remove suspended particles (Symons et al. 2000).
Explanation
The quality of raw water can be improved considerably by storage. During storage, non-colloidal, suspended particles slowly settle to the bottom of a storage tank, and solar radiation will kill some of the harmful organisms in the water. In contrast, colloidal particles remain in suspension. The smaller the suspended particles, the longer the water needs to be retained in the reservoir. If the suspended matter precipitates very slowly, chemicals can be added to induce coagulation and flocculation.
Reservoirs for sedimentation usually have two separate sections. While one is in use, the other can be cleaned. They have an intake on one side of the reservoir (or at the bottom), an outlet on the opposite side just beneath the water level, and a bottom outlet to flush the deposited material (WHO 1992).
Example
“Rapid gravity, horizontal and pressure filters can be used for direct filtration of raw water, without pretreatment. Rapid gravity and pressure filters are commonly used to filter water that has been pretreated by coagulation and sedimentation.” (WHO 1992)
References
- Symons JM, Bradley LC Jr. and Cleveland TC (2000) The Drinking Water Dictionary.
- American Water Works Association
- WHO (1992) A guide to the development of on-site sanitation
