Tennessee Wastewater Operator Practice Exam

What happens to biofilm thickness when the rotational speed of the distributor is increased?

1. Decreases

2. Remains the same

3. Increases

4. Becomes unstable

The correct answer is: Increases

When the rotational speed of the distributor is increased, biofilm thickness tends to increase. This phenomenon occurs because a higher rotational speed enhances the distribution of nutrients and dissolved oxygen, which are critical for the microbial communities present in the biofilm. As the conditions improve for microbial growth — due to better oxygenation and nutrient availability — the microbes proliferate, leading to an increase in biofilm thickness. Additionally, the increased movement induced by higher rotational speeds can promote better contact between the substrate and the microorganisms, allowing for more efficient nutrient uptake. Consequently, as the biofilm receives more resources, the overall biomass can grow, resulting in a thicker biofilm layer. In wastewater treatment systems, the balance of conditions in the system is crucial. While faster rotation may increase thickness, operators must monitor to ensure that it does not lead to problems such as detachment or sloughing off from the substrate, which could affect treatment efficiency.