Texas Wastewater Class B Practice Exam

What occurs when the dissolved oxygen levels are excessively high in an aeration tank?

1. Reduced microbial activity

2. Floc shearing

3. Settling of more solids

4. Increased nitrification

The correct answer is: Floc shearing

When dissolved oxygen levels are excessively high in an aeration tank, floc shearing occurs. This is due to the turbulence created by the excess oxygen, which can disrupt the formation of floc, the clumps of microorganisms and organic material that are essential for effective wastewater treatment. High levels of dissolved oxygen can increase the mixing intensity, leading to the physical breakdown of these aggregates. As a result, the ability of the microbes to effectively treat wastewater is compromised because smaller floc particles have less surface area to promote biological interactions. The other options do not accurately describe the effects of high dissolved oxygen levels. For example, while reduced microbial activity typically occurs under low oxygen conditions, excessive oxygen levels do not lead to a decline in microbial activity but rather can disrupt the floc structure. Similarly, settling of more solids is generally associated with optimal conditions for floc formation, not when oxygen levels are excessively high. Increased nitrification, meanwhile, refers to the biological process of converting ammonia into nitrate, which thrives at controlled and adequate oxygen levels but could be inhibited by the disruption of microbial communities due to floc shearing.