Ontario Operator-in-Training (OIT) Practice Exam

What is the correct sequence of processes in a conventional surface water treatment plant?

1. Coagulation, screening, flocculation, filtering, chlorination

2. Screens, coagulation, flocculation, filtering, chlorination

3. Chlorination, filtering, coagulation, flocculation, screens

4. Flocculation, screens, chlorination, filtration, coagulation

The correct answer is: Screens, coagulation, flocculation, filtering, chlorination

The correct sequence of processes in a conventional surface water treatment plant typically begins with screening, followed by coagulation, then flocculation, filtering, and finally chlorination. Screening is the first step, where large debris and particles are removed from the water to protect subsequent equipment and processes. After screening, coagulation occurs, where chemicals (coagulants) are added to the water to neutralize charges on suspended particles, allowing them to bind together. This process is followed by flocculation, where gentle mixing encourages these small particles to form larger aggregates called floc. Once the floc has formed, the water is passed through filtration to remove the floc and any remaining particulate matter. The final step is chlorination, in which chlorine is added to disinfect the water and ensure that harmful microorganisms are eliminated before the water is distributed for use. This sequence is essential for effective treatment, ensuring that the water meets safety and quality standards before distribution. Each step builds upon the previous one to progressively improve the clarity and safety of the water.