Water Treatment Operator-in-Training (OIT) Practice Test

Which of the following is the correct order of processes within a conventional surface water treatment plant?

1. screens, coagulation, flocculation, filters, chlorination

2. screens, flocculation, coagulation, chlorination, filters

3. chlorination, screens, filtration, coagulation, flocculation

4. screens, filters, flocculation, coagulation, chlorination

The correct answer is: screens, coagulation, flocculation, filters, chlorination

The correct order of processes within a conventional surface water treatment plant begins with screens to remove large debris and particles from the water, ensuring that subsequent treatment steps are more effective. After screening, the coagulation process follows, where chemicals are added to help small suspended particles clump together, forming larger aggregates or flocs. This is crucial because smaller particles can evade filtration if they are not adequately aggregated. Next, flocculation occurs, which is a gentle mixing process that encourages the formation of larger floc particles from the smaller ones created during coagulation. This step is vital as it helps aggregates to grow large enough to be effectively removed during filtration. Once flocculation is complete, the water is then passed through filters, which serve to remove these larger floc particles and any remaining smaller sediment. The filtration process is essential to ensure that the water is clear and free of particulates before disinfection. Finally, chlorination is performed to disinfect the treated water, killing any remaining pathogens and ensuring that the water is safe for distribution. This step typically occurs after filtering to prevent damage to the filtering media from disinfection chemicals and to ensure a clean water supply. By understanding the interdependence of these processes, it's clear why this specific sequence is