Fine Bar Screens

Bar screens are typically at the headworks (entrance) of a waste-water treatment plant (WWTP), bar screens are used to remove large objects such as rags, plastics bottles, bricks and solids from the waste stream entering the treatment plant. Bar screens are vital to the successful operation of a plant, they reduce the damage of valves, pumps, etc. Floatables are also removed at the entrance to a treatment plant, these are objects that “float” on the surface of the water and if aren’t removed end up in the primaries or aeration tanks.

The spacing between Fine bar screens is usually between 1.5 mm through 6 mm. Fine bar screens are installed at some wastewater treatment plants that do not have primary treatment to minimized clogging of downstream liquid and solid processes. Fine bar screens have been used for “effluent polishing” which increases secondary effluent to tertiary effluent quality. They also are installed upstream of the trickling filters to minimize clogging and fouling of distributor nozzles.
Typically bar screens fall under two classification, mechanical bar screens and manual bar screens. Both manual and mechanical screens contain equally spaced vertical or inclined bars that span the width of a channel. Design considerations for both mechanical and manual screens include: bar spacing, bar size, geometry of bar, channel width, angle of screen and approach velocity.

Some plants still use manually cleaned bar screens, but because they are so labor intensive, the trend is to move toward mechanical bar screens. Mechanically bar screens are the more routinely used type because of their ability to operate automatically.

In addition to the vertical or inclined bars, mechanical bar screens are equipped with rakes or some type of cleaning mechanism for removing collected debris from the face of the unit. Once screenings are collected from the unit, they are usually de-watered and hauled away to a landfill.