Which coagulant is most commonly used in water treatment?

Alum, or aluminum sulfate, is the most commonly used coagulant in water treatment because of its effectiveness and cost efficiency. When added to water, alum reacts with the natural alkalinity of the water to form aluminum hydroxide, which flocculates impurities and suspended particles. This reaction helps in removing turbidity, pathogens, and organic matter from the water, improving its clarity and quality.

The reason alum is favored in many treatment facilities is its long history of use and its proven track record in both small-scale and large-scale applications. It is widely available, relatively inexpensive, and compatible with various water conditions. Other coagulants, while effective, may not be as readily used due to either higher costs, specific pH requirements, or differing efficiencies in removing certain types of contaminants depending on the water's initial quality.