Packaged Headworks Solutions, Part 2: Common packaged headworks system designs

Drum screening with aerated grit removal basins

In this design, two tanks are used. One tank has a circulating drum screen mounted at a 25-degree angle relative to the incoming flow of wastewater. The water is screened and then flows into the aeration tank, where grit settles and is removed.

The drum screens typically use a perforated plate grid or a circular bar design. Screenings are raked or removed by water pressure by a hopper in the middle of the drum. An auger is used to remove screenings and dispose of them in an external dumpster. Two augers are located in the aeration tank. The lower one collects the grit slurry at the bottom of the tank. The other one, mounted at an angle, moves the grit to the top of the tank for disposal in a second dumpster. A grit classifier can dewater the grit slurry before further disposal.

Key features of the drum screening with aerated grit removal basins design:

• Drum screens and aerated grit removal are established technologies with many successful applications.
• Drum screens can employ either fine or coarse screening.
• Both units together require a large footprint because of the space needed for the angled screen and large grit removal tank.
• Large augers are hard to remove and service.

Drum screens with vortex grit removal basins

The drum screens with vortex grit removal basins also use two tanks with a drum screen mounted at a 25-degree angle relative to the wastewater flow into the screen. The circulating drum screens the water, which flows into a vortex tank for grit settling and removal. Like the previous design, the drum screens typically use a perforated plate grid or a circular bar design with a hopper in the middle of the drum. Screens are cleared by rakes or water pressure, and an auger removes the screenings to a dumpster.

In the vortex grit removal system, propellers or impellors rotate slowly to separate organics and aid in settling the grit. The grit slurry is eliminated from the bottom of the vortex chamber using an airlift or pump. A grit classifier can help further dewater the slurry. This packaged headworks design can be operated using a single control panel.

Key features of drum screens with vortex grit removal basins:

• This packaged headworks design uses established technologies with many successful installations.
• Drum screens can handle fine or coarse screening.
• This design requires a large footprint because of the space needed for the angled screen and grit removal tank.
• Vortex grit removal offers a lower footprint option versus aeration.
• This design requires a large auger with a motor mounted above the channel to remove screenings.
• This design provides limited dewatering of screenings.

Traveling band screens with vortex grit removal basins

This design uses two tanks: one for screening and one for grit removal. A traveling band screen is mounted at a 60-75 degree angle relative to incoming water flow, which helps capture large. The water passes through a coarse or fine perforated plat grid or a linked bar design before flowing into the vortex grit removal tank. Screenings are removed by water to a compactor. Two motors are used in this design: one to move the screening grid and another to rotate an auger that compacts the screenings. Both motors operate independently and can work at variable speeds.

Like the previous vortex system, a propeller or impellor helps settle grit. The grit slurry is removed by airlift or pump, and a classifier can aid in dewatering. This design can be operated using a single control panel.

Key features of this packaged headworks design:

• Traveling band screens and vortex grit removal are established technologies with many successful applications.
• This design supports either fine of coarse screening.
• This design requires a large footprint to accommodate the angled screen and the grit removal tank.
• The footprint for vortex grit removal is lower than aeration.
• This design provides greater compaction for dewatering than the other options discussed here.

Combined screening and grit removal in a single tank

Screening and grit removal processes can be combined in a single tank for facilities requiring a smaller footprint. Wastewater enters through an inlet duct to a center-flow traveling band screen located in the center of a cone bottom tank. This design can accommodate low velocities that promote grit settling. Collected debris is carried to the top and offloaded by water to a compactor.

The screenings are dewatered by the compactor and deposited in a dumpster. Fine grit that passes through the screens settles at the bottom of the cone tank, where the grit slurry is removed by pumping or airlifting and dewatered.

The screened and de-gritted wastewater exits through a radial launder to promote the lowest possible water velocity for grit settling. This design also uses a baffle around the screen exit below the water level to prevent turbulence and promote grit settling in the bottom of the tank.

Combining the screening and grit removal equipment into a single packaged headworks process tank can have several benefits summarized below:

• This design offers a lower overall footprint if the screen can reside inside of the grit tank.
• It offers the best configuration to prevent grit short-circuiting if the grit tank is designed with a center inlet and radial exit.
• It uses a low approach velocity to promote and improve grit settling to a grit basin under the screen.
• Integrating screening and grit removal provides the smallest footprint possible for both unit processes.
• Traveling band center flow screens can employ either fine or coarse screening.
• Center-flow screen designs can achieve high debris capture rates.
• The screen design promotes grit settling under the screening grid to the cone bottom tank.
• The design includes an overflow weir capable of full-flow screen bypass.
• The configuration of the combined system is optimized for grit settling.

Selecting the Right Screening and Grit Removal Equipment

This blog has discussed several typical packaged headworks system designs for small flow rates. Factors to consider in equipment selection include equipment footprint, screen capture, grit removal capacity, and lifecycle costs. Additional considerations should include site characteristics, such as grit and wastewater composition, when selecting the optimum system configuration for your facility.

Hydro-Dyne offers the Reef Package Headworks product designed specifically for high screening and grit capture using a compact footprint.