In treating raw water, what process comes first before filtration?

Coagulation and sedimentation are critical initial steps in the treatment of raw water before filtration occurs. During coagulation, chemicals are added to the water to facilitate the aggregation of suspended particles that can cause turbidity. This process uses coagulants such as aluminum sulfate or ferric sulfate, which bond with impurities, forming larger particles called flocs.

Once coagulation takes place, the mixture is allowed to sit in a sedimentation basin, where the flocs settle to the bottom due to gravity, effectively removing a significant portion of the suspended solids from the water. This separation process results in clearer water that is much easier and more effective to filter. If filtration were to occur before coagulation and sedimentation, the filters would become clogged more quickly and would not function effectively due to the high concentration of solids.

In contrast, disinfection, filtration media application, and activated carbon treatment are subsequent processes that follow coagulation and sedimentation in the overall treatment sequence. Disinfection aims to kill pathogens, filtration removes finer particles and impurities, and activated carbon treatment addresses taste and odor issues. Therefore, the sequence and methodology are essential in ensuring raw water is treated effectively, making coagulation and sedimentation the correct initial processes before filtration.