Why is liquid alum commonly used in surface water treatment plants?

Liquid alum, or aluminum sulfate, is primarily used in surface water treatment plants as a coagulant. Its main function is to help improve the clarity of the water by facilitating the aggregation of small suspended particles into larger flocs that can be easily removed during the sedimentation and filtration processes. By neutralizing the charges on particles in the water, alum causes them to clump together, which enhances the efficiency of filtration systems and leads to cleaner treated water.

The role of alum in water treatment does not directly focus on lowering alkalinity or making water harder. While it can affect the overall chemistry of the water, including influencing alkalinity levels, its primary and most critical function is related to coagulation rather than directly altering alkalinity. This quality of alum to create flocculation is vital for effective surface water treatment, which involves removing turbidity and improving water quality before the disinfection stage.

In addition, liquid alum does not serve as a disinfectant or a method for filtering pathogens, nor does it increase water hardness. The primary use in coagulation aligns with the importance of removing particulate matter to protect public health and ensure water quality.