Which arrangement describes lamella plate flow?

• A. parallel plates that direct the water downward then upward at 55 degrees
• B. plates inclined downward by 20 degrees then upward into plates inclined by 45 degrees
• C. plates directed downward at 45 degrees then upward at 45 degrees
• D. plates inclined by 40 degrees

Answer: (A)

Lamella plate flow uses a bank of parallel, inclined plates to create a vertical, zigzag path for the water. The water moves downward along the face of each plate and then upward into the space toward the next plate, so the flow travels downward then upward as it passes through the pack. The plates are typically set at about 55 degrees from the horizontal, which balances gravity-driven settling with enough horizontal spacing to allow upward movement between plates, maximizing settling while keeping the footprint compact. This arrangement matches the description of parallel plates directing the water downward then upward at roughly 55 degrees. The other options don’t capture the uniform, downward-then-upward path or the typical plate angle used in lamella clarifiers.