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

Aluminum sulfate, commonly referred to as alum, is frequently used as a coagulant in water treatment processes. The primary function of a coagulant like aluminum sulfate is to destabilize suspended particles in water, allowing them to clump together (or coagulate) into larger aggregates called flocs. This aggregation helps in removing impurities, such as silt, clay, and microorganisms, from the water, thus improving its clarity and overall quality.

In the coagulation process, when alum is added to the water, it dissociates and releases aluminum ions. These ions neutralize the charges on the particles present in the water, which allows them to come together and settle more easily during the following sedimentation phase. This results in a more efficient removal of solids in the water treatment process.

Other options listed, such as chlorine, fluoride, and sodium bicarbonate, serve different purposes in water treatment. Chlorine is primarily used as a disinfectant to kill bacteria and viruses, fluoride is often added for dental health purposes, and sodium bicarbonate is used to control pH levels rather than to coagulate particles. Thus, aluminum sulfate stands out as the correct choice for its specific role as a coagulant in treating drinking water.