Tennessee Wastewater Operator Practice Exam

Which conditions will require the highest airflow to achieve a DO concentration of 2mg/L in a digester?

1. Cold water, low solids

2. Warm water, low solids

3. Warm water, high solids

4. Cold water, high solids

The correct answer is: Warm water, high solids

To achieve a dissolved oxygen (DO) concentration of 2 mg/L in a digester, it is crucial to understand how temperature and solids concentration affect the oxygen demand and, consequently, the airflow required. In the scenario of warm water combined with high solids, the metabolic activity of microorganisms increases due to the higher temperature. Warmer temperatures typically enhance microbial activity, which, in turn, raises the oxygen demand because the microorganisms utilize more oxygen for respiration as they break down organic material present in the high solids content. High solids mean there is a greater volume of organic matter for the bacteria to process, which significantly increases the oxygen requirement. Given that dissolved oxygen levels are essential for the effective functioning of anaerobic digesters, maintaining sufficient airflow is critical in such a condition. The required airflow must compensate for the higher demand for oxygen to maintain the target DO concentration. This means that the combination of warm temperatures and high solids leads to the highest demand for airflow among the provided conditions, ensuring that the microorganisms remain sufficiently oxygenated to carry out their functions efficiently.