Bar screen

A bar screen is a mechanical filter used to remove large objects, such as rags and plastics, from wastewater.

[1] It is part of the primary filtration flow and typically is the first, or preliminary, level of filtration, being installed at the influent to a wastewater treatment plant.

They typically consist of a series of vertical steel bars spaced between 1 and 3 inches apart.

Items removed from the influent are called screenings and are collected in dumpsters and disposed of in landfills.

[1] As a bar screen collects objects, the water level will rise, and so they must be cleared regularly to prevent overflow.