Tennessee Wastewater Operator Practice Exam

What is the primary function of the IMLR in wastewater treatment?

1. Removes phosphorous from the water

2. Returns nitrate to the anoxic zone

3. Introduces oxygen for aerobic processes

4. Enhances sedimentation efficiency

The correct answer is: Returns nitrate to the anoxic zone

The primary function of the Internal Mixed Liquor Recirculation (IMLR) in wastewater treatment is indeed to return nitrate to the anoxic zone. This process is crucial in biological nutrient removal systems, specifically for managing nitrogen. In many wastewater treatment processes, especially those employing techniques like the modified activated sludge process, the recirculation of internal mixed liquor plays a key role in balancing the concentrations of nutrients. When nitrate is returned to the anoxic zone, it facilitates biological denitrification, allowing microorganisms to convert nitrate into nitrogen gas, which is then released into the atmosphere. This step is essential in controlling the nitrogen levels in effluent, thus minimizing the potential for eutrophication when the treated water is discharged into natural bodies of water. The other functions listed, while important in different contexts, do not capture the primary role of the IMLR as effectively as returning nitrate does. For example, the removal of phosphorus, introducing oxygen, and enhancing sedimentation are all vital in their own right, but they pertain to other stages or components of the wastewater treatment process rather than the specific function of IMLR.