Packaged Headworks Solutions, Part 1: An overview of packaged headworks technologies

Typical screening solutions

There are many screening solutions, ranging from manually raked bar screens to automatically cleared traveling band screens. The three types of screening systems commonly used in packaged headworks wastewater treatment systems are drum screens, through-flow traveling band screens, and center-flow screening equipment.

Inclined drum screen

Some packaged headworks designs utilize an inclined drum with a screen of circular bars or a perforated plate grid. The screenings can be raked into a central hopper or removed from the grid with pressurized water. Captured screenings are then moved to a dumpster with an auger. The amount of debris removed largely depends on the grid type used.

Some key considerations of the Inclined Drum Screen design are:

• Inclined drum screens require large channel widths and a large footprint and structures to house the equipment.
• Angling the auger at 25 degrees also requires a large footprint.
• Some designs use two motors: one to rotate the drum and another to run the auger conveyor.
• The auger is large and functions as a conveyer. Maintenance can be difficult if the auger must be removed.
• This design provides minimum compaction to dewater captured solids.
• A more tightly spaced grid will increase the amount of solids captured.

Traveling band screen

Band screen designs use a traveling grid that moves into the wastewater stream. Debris is captured with screens comprising either a perforated plate grid or linked bars. The screenings are removed from the grid into a compactor with either pressurized water or a rotating brush. The captured screenings are compacted and dewatered using an auger, which moves them to a dumpster. Band screen solutions typically used in wastewater treatment are center-flow and through-flow designs. Again, the amount of debris removed depends in large part on the grid type used.

Key considerations of the Traveling Band Screen design are:

• Water is typically used to move solids into a separate compactor.
• No maintenance is required on the equipment inside the channel or tank.
• This screen design supports different grid types.
• Band screen designs generally have lower headloss and footprint than drum screen designs.
• Band screens typically have higher solids capture than drum screens.

Summary of screen types used for packaged headworks (UKWIR data measured with 6mm perforated holes):

Typical grit removal solutions

Grit is traditionally defined as inorganic particles larger than 65 mesh (230 microns) and with a specific gravity greater than 2.65 g/cc. Geography and geology play a role in determining the type of grit in the wastewater system. Fine grit is typically considered to be less than 100 microns in size. The exact composition in terms of particle size and density is site-specific. Most grit removal systems in North America are designed to remove 95% of all particles larger than 300 microns and denser than 2.65 g/cc. This specification is based on an average grit composition over most regions of the US. Coastal areas typically have finer grit and require alternate settling technologies for grit removal.

Two grit removal systems are common in packaged headworks solutions: aerated grit removal chambers and vortex grit removal tanks.

Aerated grit chamber

Aerated grit removal systems have been in service for over 50 years. The typical aerated grit chambers are horizontal tanks with a bottom channel and auger conveyor that moves the grit slurry to a sump for removal. Air injected into the water column creates a circular pattern that helps settle the grit. Aerated grit chambers are designed to remove 95% of all grit 250 microns or larger with a density of 2.65 g/cc.

Vortex grit removal

Vortex grit removal systems are also an established technology and have been around for over 40 years. Vortex grit removal tanks use a stirring apparatus to move the water in a circular pattern in a circular tank. Baffles are frequently utilized in vortex designs to help with grit settling. Vortex grit chambers are designed to remove 95% of all grit 300 microns or larger with a density of 2.65 g/cc.

Summary of grit removal types commonly used for packaged headworks

Summary

In this blog, we discussed what a packaged headworks solution is and looked at the typical screening and grit removal designs used in packaged headworks systems. Our next blog will discuss the pros and cons of various packaged headworks system designs.

Speak with a Hydro-Dyne expert about your facility and which screening system is right for you. Call us at 813-818-0777 or contact us online.