Ontario Operator-in-Training (OIT) Practice Exam

What is likely to be most affected by a higher than normal BOD in wastewater entering a conventional treatment plant?

1. clarification process

2. dewatering process

3. activated sludge process

4. disinfection process

The correct answer is: activated sludge process

A higher than normal Biochemical Oxygen Demand (BOD) in wastewater significantly impacts the activated sludge process, which is a widely used method for treating municipal and industrial wastewater. The activated sludge process relies on microorganisms to consume the organic matter present in the wastewater, converting it into biomass and reducing the pollutant levels. When the BOD is unusually high, it means there is an increased amount of organic material for the microorganisms to break down. This can lead to several challenges in the process, including: 1. Increased Oxygen Demand: The microorganisms require more oxygen to decompose the additional organic material. If the available dissolved oxygen levels fall below the required threshold, it can result in inefficient treatment and even harm to the microbial community. 2. Extended Aeration Time: To effectively treat the wastewater with high BOD, the retention time in the aeration tank may need to be longer, which can lead to higher operational costs and require adjustments in the treatment plant's design and operation. 3. Potential for Overloading: If the BOD exceeds the design capacity of the activated sludge system, it can lead to poor settlement in the secondary clarifier, resulting in reduced efficiency and performance of the treatment plant. Overall, a higher BOD directly influences the activated sludge process