Screening

Screening is provided by a traveling media fine screen backed up by a manually cleaned bar screen. Separate main and bypass channels are provided with manual stop gates to control flow. The mechanical screen operates intermittently, controlled by a programmable timer capable of varying both the frequency and duration of each operating cycle. This allows operation to follow the daily flow pattern and variations in the volume of incoming screenings to minimize wear and allow screenings to dewater on the screen before being discharged to the disposal cart.

Purpose: The purpose of screening is to remove large objects that could jam equipment, plug process piping or reduce process capacity and efficiency by accumulating in process tanks.

Description: Screening is accomplished by a mechanically cleaned, fine screen. A manually cleaned bar rack is provided as a back up in case the mechanical screen fails. The screen and bar rack are arranged in parallel channels with flow controlled by aluminum stop plates.

The mechanical screen is an endless belt, self-cleaning type designed to continuously remove floating and suspended materials larger than the belt element spacing. The accumulated material is carried out of the channel and discharged into a self-dumping hopper. The screen operates intermittently to allow the screenings to partially dewater on the belt before being discharged to the hopper. Intermittent operation also reduces wear on the screen's moving parts. The self-dumping hopper is periodically emptied into a dumpster for collection by a commercial hauler and disposed of in a landfill. The screening belt consists of alternating platen and take elements mounted on parallel horizontal shafts. The horizontal spacing between elements is 15 mm (5/8"). The horizontal shafts are mounted between drive chains that creates an endless belt that is carried into and out of the channel. The drive chains are driven by an electric motor through sprockets mounted at the top of the screen unit. At the lower end of the screen, the screening belt is supported by curved guardrails. This eliminates potential problems with bearings operating under water. A rotating brush assembly located at the upper end of the screen unit cleans the screen of material that has not dropped off by gravity before the screening belt returns to the channel.

The mounting arrangement of the mechanical screen provides for rotating the screen out of the channel to a horizontal position for major maintenance operations. A lifting eye to accommodate a portable hoist is provided in the ceiling above the influent channel for this purpose.

The manually cleaned bar rack is mounted in a concrete bypass channel next to the mechanical screen. The bars are 2" x 5/16" spaced 1' apart and inclined at an angle of 60 degrees. In operation, accumulated material is periodically manually raked onto a drain plate, allowed to drain, and then shoveled into the self-dumping hopper. Access to the bar rack is provided by removable grating. A rake to fit the bar rack is provided for cleaning.