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

For thorough treatment of water, what is usually not the first step?

1. Disinfection

2. Aeration

3. Filtration

4. Coagulation

The correct answer is: Disinfection

In the process of thoroughly treating water, disinfection is typically not the first step. The reason for this is that disinfection is aimed at eliminating pathogens present in the water, and it is most effective when applied to water that has already been clarified and treated to remove sediment and other particles. Before disinfection, processes such as coagulation, flocculation, and sedimentation are generally employed to remove suspended solids and other impurities. Coagulation involves the addition of chemicals to the water that facilitate the clumping together of small particles into larger ones (floc), which then can be removed. Following coagulation, filtration is often used to further clean the water by physically removing remaining particles. Aeration can also be an early step, as it helps to remove dissolved gases and can aid in the oxidation of certain contaminants, making them easier to filter out. By the time disinfection is performed, the water should be as clear and as free of solids and suspended matter as possible, ensuring that the disinfectant can effectively target microorganisms without interference. In summary, while disinfection is a crucial step in the overall treatment process, it is not the initial operation. The first steps typically involve reduction of turbidity and removal of contaminants through coagulation and filtration