Water Treatment Operator-in-Training (OIT) Practice Test

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Which of the following is a correct order of processes within a conventional activated sludge treatment facility?

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

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

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

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

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

In a conventional activated sludge treatment facility, the sequence of processes is essential for effective wastewater treatment. The correct order starts with the grit channel, where larger, heavier particles are removed from the wastewater. This initial step is crucial as it helps prevent damage to equipment that might occur if larger debris were to enter the subsequent treatment stages. Following the grit channel, the wastewater moves to the primary sedimentation stage. In this phase, the flow is allowed to settle, which leads to the separation of the remaining suspended solids from the liquid. This process is important for reducing the biochemical oxygen demand (BOD) and removing settleable solids before the water enters the aeration tank. The aeration tank is where the activated sludge process occurs. In this step, microorganisms are introduced to the wastewater for the breakdown of organic matter. The aeration promotes the growth of beneficial bacteria, which consume pollutants, effectively treating the wastewater. Finally, the treated effluent proceeds to the secondary sedimentation stage. Here, the biomass is allowed to settle out of the treated water. This phase separates the activated sludge, which can be recycled back to the aeration tank or removed as waste. This structured approach emphasizes the importance of each process in maintaining water quality standards and effectively treating wastewater within