Which chemical is commonly used as a coagulant in water treatment?

The use of alum, or aluminum sulfate, as a coagulant in water treatment is well-established due to its effectiveness in removing suspended particles from water. Coagulation is a critical step in the treatment process, where coagulants like alum facilitate the aggregation of tiny particles into larger flocs, which can then be easily removed through sedimentation or filtration.

When added to water, alum dissociates and releases aluminum ions that neutralize the negative charges on suspended particles. This neutralization helps in clumping these particles together, promoting their deposition as a heavier mass—floc—that can be separated from the water.

Alum is favored in many water treatment facilities because it is relatively low in cost, widely available, and efficient at a range of pH levels. Furthermore, its use not only enhances the turbidity removal but can also aid in precipitating contaminants, such as phosphates, thereby improving water quality.

The other substances listed serve different purposes: chlorine is primarily used for disinfection, calcium carbonate is often used to adjust pH and hardness, and magnesium sulfate can act as a flocculant or as a nutrient but is not commonly used as a primary coagulant in water treatment.