Texas Commission on Environmental Quality (TCEQ). Class C Water License Exam

What does sand filtration primarily remove from surface water?

1. Chlorine residues

2. Turbidity

3. Pathogenic microorganisms

4. Heavy metals

The correct answer is: Turbidity

Sand filtration primarily removes turbidity from surface water due to the physical characteristics of the sand grains. Turbidity refers to the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, such as silt, clay, and organic matter. When surface water passes through layers of sand, these particles get trapped in the spaces between the grains. This process not only clarifies the water but also improves its overall quality by reducing the concentration of suspended solids. Sand filtration is essential in the treatment of drinking water because high turbidity levels can interfere with disinfection processes and may harbor pathogens. In contrast, while chlorine residues can be effectively removed through other methods such as activated carbon filtration, pathogenic microorganisms require different treatment approaches such as chemical disinfection or advanced filtration methods. Heavy metals are typically removed through processes like coagulation and sedimentation, and not primarily through sand filtration. Thus, sand filtration is specifically noted for its effectiveness in reducing turbidity in surface water.