Ontario Operator-in-Training (OIT) Practice Exam

What is the correct sequence of processes within a conventional activated sludge treatment facility?

1. secondary sedimentation, aeration tank, grit channel, primary sedimentation

2. grit channel, aeration tank, primary sedimentation, secondary sedimentation

3. grit channel, primary sedimentation, aeration tank, secondary sedimentation

4. primary sedimentation, grit channel, secondary sedimentation, aeration tank

The correct answer is: grit channel, primary sedimentation, aeration tank, secondary sedimentation

The correct sequence of processes within a conventional activated sludge treatment facility is grit channel, primary sedimentation, aeration tank, and secondary sedimentation. In this process, the initial step is the grit channel, which is crucial for removing large grit and sediment from the incoming wastewater, preventing damage to equipment and ensuring effective treatment downstream. After passing through the grit channel, the wastewater enters primary sedimentation, where heavier solids settle out due to gravity, resulting in the formation of primary sludge and a clearer effluent. Following primary sedimentation, the flow moves to the aeration tank, where biological treatment occurs. Here, microorganisms are introduced to break down organic material in the wastewater, utilizing oxygen in the process. This is a key part of the activated sludge process, promoting the growth of beneficial bacteria that further aid in purification. Finally, the treated wastewater exits the aeration tank and goes to secondary sedimentation. In this stage, the activated sludge formed during aeration settles out again, allowing for the separation of treated water from the biomass before further disinfection and release or reuse. This sequence efficiently utilizes each step to progressively treat the wastewater, ensuring that particulate matter is removed, organic materials are biologically degraded, and the final effluent meets quality standards for