Which chemical is used to increase pH levels in water treatment?

Lime, or calcium hydroxide (Ca(OH)2), is commonly used to increase pH levels in water treatment processes. When lime is added to water, it reacts with the water to form hydroxide ions, which effectively raises the pH level by reducing acidity. This is particularly important in water treatment because maintaining appropriate pH levels can help optimize conditions for disinfection processes, protect infrastructure from corrosion, and improve the overall quality of the treated water.

In contrast, the other chemicals listed either lower the pH or are not primarily used for adjusting pH. For example, carbon dioxide naturally lowers pH levels when it dissolves in water, creating carbonic acid. Hydrochloric acid and sulfuric acid are strong acids that also decrease pH when added to water. Therefore, lime is the correct choice for increasing pH in water treatment systems.