Texas Commission on Environmental Quality (TCEQ). Class C Water License Exam

What is the most common type of filter used in a surface plant?

1. Rapid sand

2. Activated carbon

3. Membrane

4. Bag filter

The correct answer is: Rapid sand

The most common type of filter used in a surface water treatment plant is the rapid sand filter. This type of filter is designed to remove suspended solids and other impurities from water through a rapid flow of water through a sand bed. The process involves forcing water through layers of sand and gravel, which captures particles and sediments effectively. Rapid sand filters operate on the principles of gravity and hydraulic pressure. When the water passes through the filter media at a relatively high rate, the larger particles are trapped on the surface, while smaller particles move deeper into the sand layer. This not only provides efficient filtration but also allows for a relatively quick backwashing process, which is essential for maintaining the filter's effectiveness. In contrast, activated carbon filters are primarily used for removing organic compounds and improving taste and odor, rather than serving as the primary filtration method for suspended solids in surface plants. Membrane filters are often more advanced and used in specific applications, while bag filters can be used, but they are typically less common for large-scale surface water treatment. Overall, rapid sand filtration is a well-established method that balances efficiency, cost-effectiveness, and ease of operation, making it the predominant choice in surface water treatment facilities.