Ontario Operator-in-Training (OIT) Practice Exam

What is one common method of secondary treatment in wastewater systems?

1. Activated sludge

2. Incineration

3. Raw filtration

4. Basic chlorination

The correct answer is: Activated sludge

Activated sludge is indeed a common method of secondary treatment in wastewater systems. This process involves aerating wastewater to enhance the growth of microbial organisms that consume organic matter. During activated sludge treatment, raw sewage is mixed with air and a population of microorganisms, usually in an aeration tank, which allows these microbes to break down pollutants effectively. This method is highly effective for reducing biochemical oxygen demand (BOD) and suspended solids in wastewater. The activated sludge process typically results in a high-quality effluent that can be safely discharged into the environment or reclaimed for reuse. The process is widely used because it can be adapted to varying flow rates and concentrations of contaminants, making it versatile for different wastewater treatment facilities. In contrast, other methods listed—like incineration, raw filtration, and basic chlorination—are not typically associated with secondary treatment. Incineration is often used for solid waste disposal rather than liquid wastewater treatment. Raw filtration may remove larger solids but does not address dissolved organics effectively. Basic chlorination can serve as disinfection but is not a treatment process aimed at reducing organic load or nutrients in the wastewater.