Aerobic Treatment Units (ATU's)

Aerobic Treatment Units (ATU) are a special kind of wastewater disposal system that are more efficient at processing waste. They are highly versatile and efficient systems and have many advantages including the ability to be installed in a place where a conventional systems could be installed (due to soil quality or site conditions), or providing the ability to build a larger house on a smaller lot (ATUs require a smaller drainfield size than conventional systems).  ATUs reduce the amount of biological material that enters your drainfield. This may extend the lifespan of your drainfield, and is more environmentally friendly than a conventional system.

There are fees associated with maintaining an ATU as a direct result of the requirments to maintain a valid operating permit and a maintenance contract for the life of the system.

How Aerobic Treatment Units Work

ATUs force compressed air through the liquid effluent in the tank to create a highly oxygenated (aerobic) environment for bacteria. Bacteria that thrive in oxygen-rich environments work to break down and digest the wastewater inside the aerobic treatment unit. Aerobic units come in a variety of sizes and shapes. They can be made of concrete, fiberglass or polyurethane.

• Pretreatment

Some ATUs have a step before the actual aeration begins. This is pretreatment and it helps to reduce the amount of solids and other materials that the bacteria cannot degrade that go into the system. These solids include grease, oil, toilet paper, and other substances that get put down the drain or flushed into the system. This stage may take place in a separate tank or in a compartment of the ATU itself.

• Aerobic Treatment Unit

The aeration chamber is where the bacteria decompose the sewage. The ATU consists of a pump, pipes, and diffusers. The pump compresses the air that flows into the chamber. The pipes carry the air from the aerator to the diffusers. The diffuser forces air into the water in the form of bubbles which introduces oxygen into the sewage. There are two main types of ATUs: suspended growth units and attached growth units. Suspended units are the most common type of ATU and work by mixing air with the sewage to feed the free floating bacteria without the use of any type of medium. In attached growth units the bacteria are attached to some type of medium located inside the ATU itself.

• Settling Chamber

The settling chamber is a calm area which allows settling to occur with the use of gravity. This is the area where the clear, treated water is separated from the bacteria that have been treating the sewage and other solids before they leave the system and travel to the drainfield.

• Drainfield

After all the treatment is complete the effluent is discharged into unsaturated soil and allowed to filter through the sand and continue further treatment. The effluent from aerobic treatment units can be discharged into a variety of different drainfield systems. There are gravel systems, chamber systems, pipe systems, and Dripline systems. All these different materials have different requirements, sizes and capacities. There are gravity feed systems and pump systems. The type of drainfield material you have present depends on what you, the builder or the engineer wanted installed.

Maintaining Your ATU

What are the requirements?

• The homeowner must maintain a current operating permit for the life of the system. The operating permit must be renewed every two years. and costs $200.00 payable to the Department of Health.
• The homeowner must maintain a valid maintenance contract with an approved maintenance entity for the life of the system.  The maintenance contract on new construction will initially be good for two years. Subsequent renewals must be good for at least a one-year term for the life of the system. Prices vary depending on the maintenance entity selected and type of system.
• Maintenance entity is required to inspect/service the ATU at least two times per year. Inspection reports must be submitted to the Department of Health in Lee County.
• The Department of Health must inspect the maintenance  and performance of the ATU at least once per year.