What is the main functional difference between a step screen and a bar screen in wastewater facilities?

• A. A bar screen uses fixed bars to remove larger solids; a step screen uses multiple narrow slots with steps to progressively remove solids.
• B. A step screen uses fixed bars to remove large solids; a bar screen uses multiple narrow slots with steps to progressively remove solids.
• C. A step screen uses multiple narrow slots with steps to progressively remove solids; a bar screen uses fixed bars to remove larger solids.
• D. A step screen uses rotating blades to remove solids; a bar screen uses moving bars to trap debris.

Answer: (C)

The main idea is how solids are captured and how openings are sized. A bar screen acts as a coarse barrier with fixed vertical bars that block larger debris while letting water pass; debris is typically removed by a rake or chute behind the bars. A step screen uses a series of narrow openings arranged in steps, so solids are caught progressively as water flows over the levels, capturing smaller solids at each step and reducing clogging and headloss. That progressive, multi-opening approach is what differentiates it from the fixed-bar, coarse screening.