Tennessee Wastewater Operator Practice Exam

What happens to excess biofilm in a fixed film process?

1. It is absorbed by the wastewater

2. It settles at the bottom

3. It sloughs off

4. It is chemically oxidized

The correct answer is: It sloughs off

In a fixed film process, excess biofilm typically sloughs off due to a combination of factors including shear forces from flowing wastewater, changes in environmental conditions, and the metabolic activity of microorganisms. As wastewater passes over the biofilm attached to fixed surfaces (such as media or walls of a bioreactor), the biofilm can become sufficiently thick that portions of it break away. This sloughing process helps to remove excess biomass from the system, allowing for a more balanced microbial population and effective treatment performance. This process is essential for maintaining the efficiency of the biological treatment because excessive biofilm can lead to reduced oxygen transfer rates and hinder overall system performance. Therefore, sloughing provides a mechanism to control the growth of microorganisms while ensuring that sufficient biofilm remains to effectively treat the wastewater. The other options do not accurately describe the fate of excess biofilm in a fixed film process. Biofilm does not simply get absorbed by the wastewater, settle at the bottom, or undergo chemical oxidation as a predominant mechanism. Instead, the dynamic nature of the system means that it regulates biofilm thickness primarily through sloughing, which is vital for optimal operation and treatment efficiency.