What aspect of water does alum primarily affect during treatment?

Alum primarily affects turbidity during water treatment. It is a coagulant used to remove suspended solids from water, contributing to clarity and overall quality. When alum is added to water, it reacts to form small, sticky particles that can bind with suspended particles, including dirt and organic matter. This process causes the combined particles to clump together, a process known as flocculation, making it easier to remove them through sedimentation or filtration. By significantly reducing turbidity, alum plays a crucial role in improving water clarity and decreasing the load on subsequent treatment processes.

While the other aspects listed—odor, chlorine demand, and microbial content—are important in water treatment, they are not the primary focus of alum's function. Odor control often involves different chemicals, chlorine demand relates to the amount of chlorine needed for disinfection, and addressing microbial content typically requires disinfectants or other strategies rather than coagulants like alum.