(ATU) Aerobic Treatment Unit

Another method of treating wastewater involves an “aerobic” process by which air is injected into the effluent in a specific manner. The increased levels of oxygen in the effluent allow the microorganisms to thrive and digest the biological nutrients. A small air compressor is used to inject air into the effluent.

By bubbling compressed air through liquid effluent in a tank, ATUs create a highly oxygenated (aerobic) environment for bacteria, which uses the organic matter as an energy source. In another stage bacteria and solids settle out of the wastewater and the cleaner effluent is distributed to a soil treatment system.

ATUs are more complicated than septic tanks. In a septic tank, solids are constantly separating from liquid. As individual bacterial cells grow, they sink to the bottom, along with less decomposed solids, to form a layer of sludge. Floating materials, such as fats and toilet paper, form a scum layer at the top of the tank.

In an ATU, the bubbler agitates the water so solids cannot settle out, and floating materials stay mixed in the liquid. Well-designed ATUs allow time and space for settling, while providing oxygen to the bacteria and mixing the bacteria and its food source (sewage). Any settled bacteria must be returned to the aerobic portion of the tank for mixing and treatment.

Services We Provide

Service Area

  • Battle Ground, WA
  • Brush Prairie, WA
  • Camas, WA
  • Hazel Dell, WA
  • Hockinson, WA
  • La Center, WA
  • Meadow Glade, WA
  • Mill Plain, WA
  • Ridgefield, WA
  • Vancouver, WA
  • Washougal, WA
  • Woodland, WA
  • Yacolt, WA