In large installations these are normally made in longitudinal concrete tanks with inclined walls. Wastewater is aerated and grit and oil are separated from the main stream.

A travelling bridge is used to facilitate the removal of accumulated grit oil-grease scum that accumulates on the liquid surface. The removal mechanism for the grit varies as it relates to the tank geometry. Usually, a submersible pump is used that is attached onto the travelling bridge and transfer sediments with liquid into an external channel.

Other method of removing grit sediments may be used such as suction hoods with syphon effect or in some cases bottom scrapers. Surface scum is removed by a travelling scraper on the liquid surface and is collected into the scum compartment. The surface scraper is automatically raised above the water level during reverse travelling of the bridge. Travelling bridges design is normally tailored to the requirements of the concrete tank construction.