Ontario Operator-in-Training (OIT) Practice Exam

Secondary treatment generally removes what percentage of BOD and suspended solids?

1. 50-75%

2. 80-99%

3. 60-85%

4. 70-90%

The correct answer is: 80-99%

Secondary treatment in wastewater treatment processes is designed to significantly reduce the organic matter and suspended solids from the wastewater after primary treatment. The process typically employs biological processes that involve microorganisms to break down organic materials. In general, secondary treatment can effectively remove around 80-99% of both Biochemical Oxygen Demand (BOD) and suspended solids. This high removal percentage is crucial for meeting environmental discharge standards and ensuring that the water can be safely released back into the environment or reused. The efficiency of secondary treatment is impacted by factors such as the design of the treatment system, the type of organisms used in the biological treatment process, and the duration of the treatment. The other options represent lower removal efficiencies that do not accurately reflect the typical effectiveness of secondary treatment systems, making them unsuitable in this context.