Flotation in water treatment is best defined as:

Flotation in water treatment refers specifically to the process of separating solids from liquids by introducing gas bubbles into the liquid. When gas bubbles are formed in the water, they adhere to suspended particles, causing them to rise to the surface. This natural tendency allows for efficient collection of the solid particles as they float, which can then be removed easily.

This method is particularly effective for treating water with low density solids or those that do not settle well with gravity alone. It is commonly utilized in various water treatment processes, such as industrial wastewater treatment and the purification of drinking water, due to its ability to enhance the removal of suspended solids, turbidity, and even some dissolved substances.

The other options relate to different water treatment processes that do not accurately describe flotation. For instance, using chemicals to disinfect water focuses on pathogen elimination, the removal of large objects from water deals with physical debris, and using sand filters relates to a different method of filtration.