The process where smaller particles in the water are combined to form larger heavier ones that sink in a settling basin is called:

The process being described is coagulation, which involves the chemical and physical aggregation of smaller particles in water to form larger, heavier aggregates, commonly referred to as flocs. When coagulants, such as aluminum sulfate or ferric chloride, are added to water, they neutralize the charge of suspended particles, allowing them to bond together. As these aggregates become larger, they gain sufficient mass to settle out of the water column in a settling basin, effectively removing turbidity and other impurities from the water.

Coagulation is a crucial step in water treatment processes, as it enhances the efficiency of subsequent filtration and disinfection stages, leading to cleaner and safer water supplies for consumption and use.

Other processes mentioned, such as pre-sedimentation, are related but are distinct from coagulation. Pre-sedimentation refers to allowing larger particles to settle out before further treatment, while disinfection focuses on eliminating pathogens, and oxidation involves chemical reactions that transform substances rather than combining particles.