Clarifiers are settling tanks engineered for continuous separation of solids from water by allowing heavy suspended solids to settle at the bottom and clarified water to overflow out to the top. The sludge layer produced at the bottom and the floating scum needs to be removed or thickened for proper disposal. The clarified water or wastewater then goes through the next treatment stage.
Suspended matter can consist of large and denser solids which can settle by gravity alone, or finer and colloidal solid particles that will stay in suspension and will not settle. In this case, coagulation and flocculation agents are required to clump together the finer particles and enhance the settling rates.
- Coagulation can be achieved through the controlled addition of iron, aluminum or inorganic salts.
- Flocculation can be enhanced through the controlled addition of water soluble organic polymers.
For potable water treatment, the clarifier is utilised as primary treatment to remove suspended and colloidal particles before sending the clarified water to the membrane filtration and disinfection stages.
For wastewater treatment, the clarifiers are used as either primary or secondary clarifiers. Similar to a potable water treatment process, the primary clarifier removes large suspended solids prior the biological treatment stage. Secondary clarifier receives the mixed liquor (treated wastewater mixed with biomass) from the bioreactors (e.g. Activated Sludge, MBR, and Oxidation Ditch) and separates the biomass (sludge flocs) from the treated wastewater. In most biological treatment processes, majority of the separated biomass are returned back to the bioreactor.