What is the primary purpose of adding chemical/coagulate aids during treatment?

The primary purpose of adding chemical or coagulant aids during water treatment is to enhance flocculation and settleability. Coagulants work by neutralizing the charge on suspended particles in the water, allowing them to clump together into larger aggregates, known as flocs. This process is crucial because larger flocs are more easily removed from the water through sedimentation or filtration.

By improving the properties of the flocs, coagulant aids ensure that these aggregates settle out of the water column more efficiently, reducing turbidity and improving overall water quality. Enhanced settleability means that the solid particles can be removed more effectively before the water goes through additional treatment processes, like filtration, ultimately leading to cleaner drinking water.

Focusing on the other options, reducing water temperature does not directly relate to the process of coagulation and flocculation. Similarly, while speeding up filtration rates may be a secondary benefit of improved floc properties, it is not the primary purpose of adding coagulants. Decreasing chemical usage is a relevant goal in water treatment practices, but it is not a direct purpose of adding coagulant aids, since their addition is meant to optimize the treatment process, often requiring careful dosage to achieve desired outcomes.