Wastewater Treatment Operator Certification Practice Test

What could cause the slime growth on a rotating biological contactor to appear black?

1. It could indicate solids or organic overloading

2. High DO in the plant effluent

3. Lack of BOD in the influent to the rotating biological contactor

4. Low hydraulic loading

The correct answer is: It could indicate solids or organic overloading

The presence of black slime growth on a rotating biological contactor often indicates a condition related to solids or organic overloading within the system. When the microbial population is subjected to an excessive amount of organic material or solids, it can lead to an unhealthy growth of microorganisms. This overabundance can facilitate the rapid proliferation of certain types of bacteria, particularly those that produce dark pigments or have a different morphology that results in a darker appearance. In biological treatment processes, maintaining a proper balance of organic loading is critical for the health and function of the biomass. If the organic loading is too high, it can overwhelm the biological treatment process, inhibit the growth of beneficial microorganisms, and lead to the development of adverse conditions in the reactor. The black slime typically signifies not only overloading but may also indicate the presence of specific types of microorganisms that thrive in these conditions, exacerbating issues related to treatment efficiency and system operation. Thus, identifying black slime growth as a symptom of solids or organic overloading is vital for wastewater operators to take corrective actions and maintain effective treatment performance.