Which of the following is NOT a limitation of the lime softening process?

In the context of lime softening, option D is correct because it accurately reflects the capability of the process. Lime softening is primarily employed to reduce hardness in water by precipitating calcium and magnesium ions. However, one of the key aspects of lime softening is that it does not effectively remove all hardness components. Specifically, while it is designed to target certain hardness ions, other forms, such as non-carbonate hardness, may not be fully removed.

This process can remove some components of hardness, especially when performed under optimized conditions, but due to various variables such as water chemistry and the specific types of hardness present, complete removal of all hardness is generally not achieved. Therefore, stating that it effectively removes all hardness components is incorrect.

Understanding the limitations of lime softening is crucial for water treatment operators, as it helps to inform them about potential additional treatment steps that may be necessary to address remaining contaminants, including certain hardness components that lime softening does not fully address.