Tennessee Wastewater Operator Practice Exam

What can reduce oxygen transfer efficiency and resulting DO concentrations in a digester?

1. Temperature variations

2. Total solids concentration >3.5%

3. Low aeration rates

4. High loading rates

The correct answer is: Total solids concentration >3.5%

The total solids concentration in a digester plays a significant role in oxygen transfer efficiency because higher concentrations of solids can hinder the movement of oxygen throughout the liquid. When total solids exceed a certain level (in this case, more than 3.5%), the density of the material increases, which can create a more viscous environment. This viscous environment obstructs the diffusion of oxygen into the liquid, thereby leading to lower dissolved oxygen (DO) concentrations. In digesters, maintaining an optimal balance of total solids is crucial to ensure that there is enough liquid space for effective gas exchange and for the microorganisms responsible for digestion to thrive. When the concentration is too high, it can also lead to stratification within the digester, making it even more challenging for oxygen to reach all areas equally. Understanding how solute concentrations affect oxygen dynamics is essential for operators managing wastewater treatment systems, as inadequate DO levels can significantly affect treatment efficiency and the overall health of the microbial community within the digester.