Tennessee Wastewater Operator Practice Exam

If the influent BOD decreases, what happens to the growth of new bacteria in the secondary treatment process?

1. Increases significantly

2. Decreases to match the influent BOD supply

3. Remains unchanged

4. Fluctuates randomly

The correct answer is: Decreases to match the influent BOD supply

In the context of the secondary treatment process in wastewater management, the growth of new bacteria is closely related to the amount of biodegradable organic matter available, which is primarily measured by biochemical oxygen demand (BOD). When the influent BOD decreases, there is less organic material available for the bacteria to metabolize. Bacteria in the activated sludge process utilize BOD as a food source for growth and reproduction. Therefore, when the BOD concentration goes down, the stimulation for bacterial growth also diminishes because there is insufficient substrate to support a larger bacterial population. As a result, the bacterial growth rate will decrease to match the lower influent BOD supply. This relationship reflects a biological mechanism where microbial populations adjust based on the availability of nutrients, ensuring that they don't overpopulate in an environment where food resources are limited. Thus, the level of bacteria in the treatment system will align with the reduced organic load, leading to a decrease in their growth in response to the decrease in influent BOD. Understanding this connection is crucial for wastewater operators to maintain efficient treatment processes.