Which of the following is a common form of lime used in wastewater treatment?

Calcium oxide is commonly used in wastewater treatment processes. It serves as a strong alkaline agent and is effective in pH adjustment and the precipitation of heavy metals. When added to wastewater, calcium oxide reacts with water to form calcium hydroxide, which increases the pH and facilitates the removal of contaminants through various chemical processes, including coagulation and flocculation. This helps improve the overall quality of the effluent before it is discharged or further treated.

Other options, while they may have specific uses in certain contexts, do not serve as the primary lime in wastewater treatment processes. For instance, calcium carbonate is generally used for buffering and might not be as effective as calcium oxide in raising pH quickly in treatment scenarios. Calcium sulfate is more commonly associated with gypsum, used in construction and agriculture rather than wastewater treatment, and magnesium hydroxide is not as widely utilized as a lime product in this context.