California Wastewater Treatment Operator Practice Exam

What will the addition of chlorine gas do to the pH of wastewater?

1. increase the pH

2. decrease the pH

3. have no effect

4. stabilize the pH

The correct answer is: decrease the pH

The addition of chlorine gas to wastewater typically leads to a decrease in pH. Chlorine is a strong oxidizing agent, and when it reacts with water, it forms hydrochloric acid (HCl) and hypochlorous acid (HOCl). These acids contribute hydrogen ions (H+) to the solution, causing the pH to drop. This effect is significant in wastewater treatment processes where chlorine is often used for disinfection purposes. It’s important for operators to monitor pH levels because a decrease in pH can impact the efficacy of other treatment processes and the overall health of aquatic environments when effluent is discharged. Understanding the relationship between chlorine gas and pH is crucial for managing the treatment process effectively, ensuring that the water remains within acceptable limits for both the treatment system and environmental discharge regulations.