Water clarifiers are chemical or physical treatment processes and equipment designed to remove suspended solids, colloidal particles, and turbidity from water, resulting in a clear effluent. In municipal and industrial treatment, the most common method involves the use of coagulants and flocculants. Coagulants (like aluminum sulfate/alum, ferric chloride, or polyaluminum chloride) neutralize the electrical charges on fine particles, causing them to destabilize and clump together into microflocs. Then, flocculants (typically high-molecular-weight polymers) bridge these microflocs to form larger, heavier aggregates called flocs. These dense flocs then settle out of the water by gravity in a settling tank or clarifier basin, a process known as sedimentation, leaving clarified water above.

The applications of clarifiers are fundamental to water and wastewater treatment across numerous sectors. Municipal drinking water plants use them to produce clear, safe water from surface sources like rivers and lakes. Industrial wastewater treatment relies on them to remove process solids before discharge or reuse, common in industries like mining, textiles, and food processing. Municipal wastewater treatment plants employ clarifiers as a primary treatment step to remove settleable solids and as secondary clarifiers to separate biological floc (activated sludge) after the aeration process. Other types include lamella clarifiers, which use inclined plates to increase settling area in a compact footprint, and dissolved air flotation (DAF) units, which use microbubbles to float lighter particles to the surface for removal. The effective selection and dosing of chemicals, along with proper clarifier design, are critical for achieving regulatory compliance, protecting downstream processes, and ensuring efficient operation.