Florida Drinking Water Operator "B" Practice Test

What is the common effect of adding acid to chlorinated water?

1. Increases pH

2. Decreases chlorine efficiency

3. Forms chloramines

4. Neutralizes THM's

The correct answer is: Decreases chlorine efficiency

When acid is added to chlorinated water, the pH of the water decreases. This change in pH can have a significant effect on the efficiency of chlorine as a disinfectant. Lowering the pH generally leads to an increase in the concentration of hypochlorous acid, which is the more effective form of chlorine for disinfection. However, at extremely low pH levels, chlorine can become less effective due to its instability and the potential formation of disinfection byproducts, which can interfere with its ability to kill pathogens effectively. This demonstrates the importance of maintaining balanced pH levels for optimal chlorination. Operators must monitor and adjust the pH to ensure that chlorine remains effective in its role as a disinfectant, which ultimately protects public health. In contrast, forming chloramines typically occurs when ammonia is present in water during chlorination, increasing the complexity of the disinfection process. The other effects listed, such as neutralizing THMs (trihalomethanes), are also influenced by several variables in water chemistry and do not specifically relate to the direct impact of adding acid to chlorinated water. Understanding these interactions reinforces the need to manage chemical dosing carefully in water treatment processes.