Ontario Operator-in-Training (OIT) Practice Exam

Which method is NOT commonly used for dewatering sludge?

1. Centrifuging

2. Drying beds

3. Filtration

4. Gas fumigation

The correct answer is: Gas fumigation

The correct choice is indeed the method that is not commonly used for dewatering sludge, which is gas fumigation. Dewatering sludge is typically achieved through physical methods that remove water from the sludge, and gas fumigation does not fit into this category. Centrifuging, drying beds, and filtration are all well-established techniques used in the treatment of wastewater solids. Centrifuging employs a fast-spinning mechanism that utilizes centrifugal force to separate solids from liquids, effectively reducing the volume of sludge. This method is efficient and can handle varying sludge types. Drying beds, on the other hand, rely on the natural evaporation of water from the sludge in an open bed system, allowing the liquid to drain away while the solids are left behind. This process is cost-effective and works well in regions with adequate sunlight and dry conditions. Filtration involves passing sludge through a medium that captures the solid particles while allowing water to pass through. This method can also be highly effective in reducing sludge volume. In contrast, gas fumigation is a technique used for pest control and does not apply to the dewatering of sludge, which requires physical or mechanical processes to achieve the separation of water and solids. Thus, it stands out as an incorrect option