In coagulation and flocculation tank, wastewater is allowed to react with coagulants and flocculants, respectively, with appropriate concentration and amount (determined by Jar testing). These chemicals reduce the stability of colloidal particles in water, which enables the particles to interact with each other to form larger flocs. As a result, the process provides a good condition for sedimentation and floatation in respectively downstream sedimentation tanks or DAF tanks. The removal of flocs from wastewater in sedimentation tanks and DAF tanks is implemented using density differences.

This process is often applied to remove color, suspended solids, some heavy metals as well as part of organic pollutants in wastewater.

Koastal Eco utilizes the coagulation and flocculation process in most industrial wastewater treatment plants.


Sedimentation tank is operated according to gravity settling to separate suspended solids or flocs created from coagulation and flocculation tank. Settled sludge collected by sludge collection hopper will be pumped to the sludge treatment system while treated wastewater will overflow to the next treatment unit.

Types of sedimentation tanks commonly used:

  • Circular tank (with bottom scraper)
  • Rectangular tank (with bottom scraper)
  • Hopper bottom tank (for small flowrate projects)
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Circular sedimentation tank


Sedimentation tank separate suspended solids or flocs by gravity settling mechanism, and DAF tank removes them by floatation mechanism. Wastewater after going through a flocculation tank is compressed at high pressure (3-4atm), then reduced to atmospheric pressure in DAF tank. The dissolved air separated from wastewater forms fine air bubbles, which will adhere to the suspended solids in the wastewater and cause them to float to the surface. They will then be removed by a skimming device.

In wastewater treatment, DAF tank is used to remove fat, oil, grease, suspended solids, surfactants, and low-density solids (pulp and paper, rubber industry, etc.). Koastal Eco has applied DAF tank with the capacity up to 8,000 m3/day

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Dissolved Air Flotation DAF

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