Tennessee Wastewater Operator Practice Exam

Which chemical is commonly used as a flocculant in wastewater treatment?

1. Alum

2. Soda ash

3. Caustic soda

4. Hydrochloric acid

The correct answer is: Alum

Alum, or aluminum sulfate, is widely used as a flocculant in wastewater treatment processes. A flocculant is a substance that helps aggregating tiny particles into larger particles, called flocs, which can then settle out of the liquid phase more easily. In wastewater treatment, this process is crucial for removing suspended solids and colloidal particles, improving the clarity of the water. When alum is added to wastewater, it reacts with the water to form microflocs. These microflocs then collide with larger particles, allowing them to clump together and form larger flocs that can be removed through sedimentation or filtration processes. This mechanism effectively reduces turbidity and enhances the overall efficiency of the water treatment system. In comparison, soda ash is primarily used for pH adjustment and to soften water rather than as a flocculant. Caustic soda is also aimed at pH adjustment and is used in various chemical reactions, while hydrochloric acid is primarily used as a strong acid for lowering pH levels but does not serve as a flocculant. Therefore, alum stands out as the compound specifically designed and used for promoting flocculation in wastewater treatment.