Florida Drinking Water Operator "B" Practice Test

What action should be taken if excess calcium carbonate is precipitating on the filters in a lime softening plant?

1. Add more lime to the process

2. Add carbon dioxide to lower the pH

3. Increase the filter speed

4. Remove the filters entirely

The correct answer is: Add carbon dioxide to lower the pH

When excess calcium carbonate is precipitating on the filters in a lime softening plant, adding carbon dioxide to lower the pH is the appropriate action. This occurs because calcium carbonate tends to precipitate out of solution at higher pH levels. By introducing carbon dioxide, the pH of the water can be reduced, which helps to maintain the calcium carbonate in a soluble form, thereby preventing it from accumulating on the filters. This adjustment is particularly important for maintaining the efficiency of the filtration process, as excessive deposits can hinder flow rates and reduce the overall effectiveness of the softening treatment. Lowering the pH also alters the solubility dynamics, allowing the system to effectively manage calcium levels without causing undue build-up in the filtration media. Adjustments to pH are a common practice in water treatment to balance chemical interactions and optimize processes, making this option a suitable response to the issue of excess calcium carbonate precipitation.