The Problem

A variety of different screen flow patterns and screening medias have been applied to the headworks of sewage treatment plants over the past century. Each type of screen came with numerous inherent flaws that either prevented efficient screening or required constant maintenance. Pursuant to discharge demands requiring a round hole, ordinary perforated plate has been applied to the oldest mechanical screen design, the Thru Flow band screen. The thin perforated plate (usually 1/16" or 2mm thick) allows fibrous debris such as body hair, cotton and rags to staple or hair pin around the plate eventually blinding the screen. Removal requires constant attention and/or an additional rotating brush or spray. The Thru Flow pattern allows material missed by the brush or spray to simply carry over to the clean side thus fouling other down stream operations within the plant.

The Solution

Brackett Green’s engineers spent several years working with various combinations of plate thickness and hole diameters to develop a screening media that would resist hair pinning. The end result is known today as the ProPaPanel® (US Patent No. 5407563). This thick plate (9mm/3/8") screening media resists hair pinning, contains a tapered hole to prevent plugging and is made of a corrosion resistant urethane. The combination of unique benefits of the ProPaPanel and the superior in to out central flow pattern establish the CF 200 as a highly economical solution. ProPaPanels are available with 6mm (~1/4") diameter to 2mm (~1/16") diameter holes. The ProPaPanel also requires a low backwash pressure (~30 PSI) to positively clean the screen. This same wash water is typically used up to three times: once to backwash the screen, again to transport the screenings via gravity conveyance and a third time in the screenings conditioning process. Today Brackett Green has hundreds of CF 200 Screens installed at sewage treatment, water reclamation facilities and combined stormwater overflow plants around the world.

The Process

The influent water enters the CF 200 in the center of the screen and passes through each side of the screening band as the band revolves. Clean water exists through either side and recollects into a smaller down stream channel. ProPaPanels retain the smaller debris while lifting lips (debris scoops) (1) mounted on every panel elevate the larger screenings to deck level. When the debris laden panels reach deck level, the captured screenings are deposited into a center trough by gravity and a light backwash (2) (typically 30 PSI) rinses the panels clean. The captured screenings then exit the head section via a sluice trough (3) eliminating the need for screw conveyors.

Other Features

Frame tracks (4) are sealed to eliminate the bypass of solids and to prevent grit from entering the chain tracks. Other features include shaft mounted drive (5) and anti-friction bearings (6) to reduce maintenance. Enclosed head section (7) with viewing windows for odor control. Trough spray nozzle (8) to convey screenings. Rigid frame construction (9) for durability and long life. Sealed back plate eliminates bypassing. Roll around foot section (10) to eliminate foot sprockets and reduce maintenance. Positive sealing so that nothing larger than the mesh opening can bypass the screen. The CF 200 is the best screen for the fine filtration of waste water. The CF 200 utilizes state-of-the-art design for the filtration of domestic sewage, eliminating both carryover and bypassing of solids downstream.