Coagulation / Settlement Tanks are used for a wide variety of applications which require the addition of chemicals to the water being treated to form precipitates and settle suspended solids in the raw water. Applications include the addition of lime to raw water in the cold lime softening process, which also reduces the alkalinity of the raw water, and addition of lime or other alkalis to effect precipitation of insoluble hydroxides.

High performance, rapidly deployable settlement tank (silt traps) ensuring effective removal of suspended solids from wastewater providing a large settlement area within a small footprint.  The water to be treated is often mixed with the chemicals and flows down to the base of the coagulation vessel via the central chamber. The water then flows up the outside of the chamber where the suspended solids and precipitates settle out.   The solids (sludge) collected by the unit settle within the unit’s single hopper and are easily removed by the opening of a gate valve, eliminating the need for the unit to be taken off line for emptying thus allowing continuous operation.  The treated water is collected at the top of the vessel.

Silt whilst technically referring to a specific grain size is more often a broad term applied to fine particles of soil carried by water giving it that muddy or dirty discoloration. The most common source of silt pollution is the result of rainwater runoff from topsoil stripped areas of construction sites. When washed off into nearby watercourses, silt pollution is highly visible and easily traceable back to the site. It can travel a long way, causing significant environmental harm including suffocating fish by blocking gills and settling on river beds killing bottom dwelling organisms. There are legal limits for the concentration of suspended solids in discharged water and breaching these is a common reason for construction companies being taken to court and fined. 

Primary treatment of sewage is removal of floating and settleable solids through sedimentation. Primary clarifiers reduce the content of suspended solids as well as the pollutant embedded in the suspended solids.  Because of the large amount of reagent necessary to treat domestic wastewater, preliminary chemical coagulation and flocculation are generally not used, remaining suspended solids being reduced by following stages of the system.

Sedimentation tanks are used in water treatment as “secondary clarifiers” to remove flocs of biological growth created.

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