What type of water treatment method typically involves the use of alum?

The use of alum, or aluminum sulfate, is closely associated with the coagulation process in water treatment. Coagulation is a crucial step designed to remove suspended solids and colloidal particles from water. When alum is added to water, it reacts to form small particles known as flocs, which aggregate together and settle out of the water due to gravity. This process effectively improves water clarity and reduces the load on subsequent filtration systems.

Coagulation is essential because it enhances the efficiency of filtration and disinfection processes that follow. By promoting the aggregation of particles, it allows for the easier removal of contaminants before reaching the disinfection stage. In contrast, filtration is primarily focused on physically removing particles from water, while disinfection targets pathogens through chemical means or by using ultraviolet light, and fluoridation is related to adding fluoride for dental health benefits. Thus, the role of alum in coagulation directly makes it the correct answer in this context.