To prevent buildup in the flocculation basin, which of the following actions should be taken?

To effectively prevent buildup in the flocculation basin, increasing the speed of the paddle is crucial. This action enhances the mixing and agitation within the basin, which is necessary for promoting the collision and aggregation of particles, thereby facilitating the flocculation process. By increasing the paddle speed, you ensure that the particulate matter remains suspended and is effectively mixed with the coagulant, preventing the settling of flocs or debris at the bottom.

Furthermore, higher paddle speeds help create a controlled flow regime that supports continuous movement of the flocculent material. This minimizes the likelihood of stagnant zones where sediment might accumulate, ensuring that the water treatment process operates efficiently and that higher quality treated water is produced.

Other choices, such as reducing paddle speed or adding more coagulant, could lead to either insufficient mixing or excessive chemical use without addressing the underlying issue of buildup. Increasing water temperature may also influence viscosity and reaction rates but does not directly tackle the buildup concern as effectively as adjusting paddle speed.