Tennessee Wastewater Operator Practice Exam

Which conditions tend to entrain grease and prevent its removal in a primary clarifier?

1. High pH and low temperatures

2. Low pH and high temperatures

3. Neutral pH and moderate temperatures

4. High pH and high temperatures

The correct answer is: Low pH and high temperatures

Entrainment of grease in a primary clarifier can be influenced by various chemical and physical conditions in the wastewater treatment process. The correct choice highlights how low pH combined with high temperatures can create the ideal environment for grease to become entrained rather than removed effectively. In situations with low pH, the solubility of grease can increase, leading to a reduction in the surface tension of the water. This allows the grease to remain in suspension, making it more difficult for the primary clarifier to remove it effectively. Additionally, high temperatures can decrease the viscosity of grease, further facilitating its suspension in the wastewater stream. The combination of these two factors—low pH providing a favorable environment for grease dispersion and high temperatures aiding its movement—results in a scenario where grease is more likely to be entrained rather than settled out at the clarification stage. Understanding the chemistry of wastewater in terms of pH and temperature is critical for effective operation and management of clarifiers, as maintaining optimal conditions can significantly improve removal rates of grease and other floating materials.