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Environmental Services

working for clean rivers

Phone: 503-823-7740

Fax: 503-823-6995

1120 SW 5th Avenue, Suite 1000, Portland, OR 97204

Glossary of Terms

  • Headworks The door to the treatment process where contaminants larger than 3/4" in diameter are removed.
  • Screenhouse Grit removal and screening devices are installed here.
  • Clarifier A large, circular or rectangular tank that separates solids from the waste stream by settling or flotation.
  • Flights Slats that move along the bottom or surface of a rectangular clarifier to transport settled or floating material to removal points.
  • Skimmers A device that removes grease or scum from the surface of wastewater in a clarifier or tank.
  • Aeration Tank A tank normally associated with secondary treatment where air is injected to provide oxygen for microorganisms and to bring them into contact with wastewater through the mixing action.
  • Blowers Low pressure air compressors that inject air into the aeration tank.
  • Anoxic Selector The section of an aeration tank where oxygen is available in a combined form rather than as dissolved O2 to select out undesirable types of bacteria.
  • Anaerobic Digester A closed vessel where solids, or sludges, produced by other treatment processes are stabilized through a biological process which takes place in the absence of oxygen.
  • Thickener Equipment or process that increases the concentration of solids in sludge after gravity sedimentation.
  • Biosolids Treated wastewater sludges that meet stringent quality control standards.
  • Suspended Solids Insoluble solids that either float on the surface of or are in suspension in wastewater or other liquids.
  • Return Activated Sludge (RAS) Sludge that is recycled between secondary clarifiers and aeration tanks to maintain an active biomass for secondary treatment.
  • Thickened Waste Activated Sludge (TWAS) Solids removed from the activated sludge process and passed through a thickening process or thickening device.

Heartbleed Security Notice

A serious security vulnerability known as "Heartbleed" was recently discovered in OpenSSL, a popular software library commonly used by many websites on the internet to encrypt communication between a user's computer and a web server.

PortlandOregon.gov is NOT affected by this vulnerability as it does not use the OpenSSL software library. Please rest assured we are dedicated to protecting your security on this website.