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1) Screen it

Portland Water District
Portland, Maine

PROBLEM

The Portland Water District provides wastewater services to six communities in southern Maine. Assets include 72 pump stations ranging from an ejector station serving several homes to the state’s largest at 50 mgd; four treatment plants; and 96 miles of pipe.

The capital improvement plan included upgrading a pump station that feeds a 4.54-mgd treatment plant. Shortly after installation, the new pumps began to plug at the onset of wet weather. Two of the four pumps would fail completely. The other two would keep running with the clogs intact, making the entire facility vibrate.

Made entirely of baby wipes, according to Portland Wastewater Services Director Scott Firmin, the clogs were physically degrading the pumps. The district considered three possible solutions:

  • New cutter pumps or impeller modifications. Rejected; available electrical power at the station limited possible pump modifications.
  • A channel grinder. Rejected; equipment couldn’t easily accommodate station configuration and flow ranges, and instead of removing material would pass it along to the plant where there could be downstream issues.
  • Screens. Accepted; the station already had a coarse bar rack, so it could accommodate a screen.

SOLUTION

Equipment: Mahr continuous-rake screen with ½-inch bar spacing. It’s a front-raked, front-return bar screen with multiple rake bars mounted to chains located on each side of a self-contained frame to prevent solids carryover.

Manufacturer: Headworks Inc.
www.headworksusa.com

Equipment: Model EWP 250-600A washing press to control odor by rinsing organic matter out of screenings material.

Manufacturer: Vulcan Industries Inc.
www.vulcanindustries.com

AEC firm: CDM, using design-build EPCM (engineer-procured contract management) with a $4 million guaranteed maximum price

Project cost: $3.74 million

FOR MORE INFORMATION
Scott Firmin
sfirmin@pwd.org
207-774-5961, ext. 3077
Portland Water District
www.pwd.org

Next page: 2) Replace the pump