Ontario Operator-in-Training (OIT) Practice Exam

What is the purpose of a sedimentation tank in water treatment?

1. To reduce water pressure

2. To remove dissolved gases

3. To allow solid particles to settle

4. To disinfect the water

The correct answer is: To allow solid particles to settle

The purpose of a sedimentation tank in water treatment is to allow solid particles to settle out of the water. This process relies on gravity to remove suspended solids, such as silt, sand, and organic matter, from the water being treated. During sedimentation, heavier particles sink to the bottom of the tank, forming a sludge layer, while clearer water rises to the surface and can be further processed. This is a critical step in water treatment as it helps to improve the efficiency of subsequent treatments, such as filtration and disinfection, by reducing the load of solids that would otherwise need to be handled in those processes. The sedimentation process ultimately leads to cleaner water, minimizing the potential for contamination and making it safer for consumption and use.