Tennessee Wastewater Operator Practice Exam

Why might alum be added upstream of the primary clarifier?

1. To lower the pH

2. To improve clarifier performance

3. To increase dissolved oxygen

4. To reduce odor

The correct answer is: To improve clarifier performance

Adding alum upstream of the primary clarifier is primarily done to enhance the performance of the clarifier. Alum acts as a coagulating agent, aiding in the aggregation of suspended particles and colloids in the wastewater. When alum is introduced, it reacts with the particles, causing them to form larger aggregates or flocs. This improved flocculation makes it easier for these particles to settle out in the clarifier, leading to a clearer effluent and reducing the overall turbidity of the water. By improving clarifier performance, alum helps in achieving more effective removal of solids and other impurities before the wastewater moves on to further treatment processes. This step not only optimizes the overall efficiency of the treatment plant but also enhances the quality of the treated wastewater that is ultimately discharged or reused. While alum does have other effects, such as potentially lowering pH or influencing dissolved oxygen levels, these are not the primary reasons for its use in this context. The main focus is on the coagulation and flocculation processes, which directly impact the efficacy of the primary clarifier.