How an Aerobic Treatment Unit (ATU) Works

The Suspended Growth Aerobic Treatment unit (ATU) consists of an aeration compartment, diffusers, a clarification compartment and an outlet assembly. As the wastewater from the home enters the aeration compartment it is thoroughly mixed with the contents which are full of mixed liquor suspended solids (MLSS) activated sludge (aerobic bacteria). The diffusers are responsible for this mixing. They also dissolve large quantities of oxygen into the mixed liquor which will be utilized by the aerobic bacteria in the treatment process. This is also known as Extended Aeration. The aerobic bacteria utilizes the incoming wastewater as a food source and metabolizes or consumes it.

For every gallon of wastewater that enters the aeration compartment an equal amount is hydraulically displaced into the bottom of the clarification compartment. Due to the calm condition in the clarifier as the mixed liquor moved upward toward the outlet assembly, suspended solids (bacteria) settle to the bottom where they reseed and remix with the aeration compartment mixed liquor (aerobic bacteria). This reseeding keeps the aerobic bacteria strong and healthy and the remixing provides additional biological treatment. The remaining treated and clarified effluent leaves the Aerobic Treatment Unit (ATU) via the outlet assembly and outlet pipe.

Typical ATU

This effluent is highly treated and odorless!

Typical Samples Showing Proper Performance of an Aerobic Treatment Unit (ATU)

  • Aeration grab sample
  • Mixed Liquor Suspended Solids (MLSS) immediately caught from aeration compartment
  • Healthy mixed liquor
  • Chocolate in color and resembling small bits of sponge
  • Mixed Liquor Suspended Solids (MLSS)
  • 15 minute Settleability test started immediately after being caught from aeration compartment
  • Healthy settleability test
  • 20% – Good interface after 15 minutes of settling
  • Effluent from ATU outlet
  • Highly treated
  • Clear
  • Odorless

The above samples are from an actual True Aerobic ® converted septic tank (ATU).

Patents Pending