Tennessee Wastewater Operator Practice Exam

Alum is added to the secondary clarifiers of an activated sludge plant to remove?

1. Nitrogen

2. Phosphates

3. Suspended solids

4. Organic matter

The correct answer is: Phosphates

Alum, or aluminum sulfate, is commonly used in wastewater treatment as a coagulant to help remove phosphorus, particularly in processes that involve secondary clarifiers in activated sludge plants. When alum is added to the wastewater, it reacts with the phosphorus compounds present, forming aluminum phosphate. This reaction facilitates the precipitation of phosphorus from the water, allowing it to be removed along with the settled solids during the clarification process. Reducing phosphorus is critically important in wastewater treatment because excess phosphorus can lead to eutrophication in receiving water bodies, causing harmful algal blooms and degrading water quality. Thus, the addition of alum effectively targets and addresses the removal of phosphates, enhancing the overall efficiency of the treatment process.