How does an aerator septic system work?

Written by stephen hasty
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How does an aerator septic system work?
Individual septic systems with aeration resemble large municipal aeration sewage treatment systems. (Thinkstock Images/Comstock/Getty Images)

Conventional septic systems utilise anaerobic treatment of waste water in a septic tank. Aerator systems, or aerobic treatment units (ATU), create an oxygen-rich environment using aerators and air compressors. ATUs are used primarily as a pretreatment device in instances where high-quality effluent is needed, such as when poor soil exists for the septic system's drain-field. ATUs reduce pathogens and break down organic material at a much faster rate than anaerobic systems.

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Motors and Aerators

Air supply is provided through the application of a blower motor or an aerator. Blower motors push air through diffusers or bubblers. Aerators submerged in the waste water pull outside air into the mixed portion of the tank with vacuum. Aeration units may be retrofitted to existing tanks or may be installed as a separate unit. Protecting aeration devices from damage or plugging requires installation of a primary tank or trash trap that will catch large debris.

Pump Controls

Aeration systems can be utilised on a gravity system or a pump system. For the best-quality effluent, aerobic treatment units require waste water dosages to be strictly controlled. Waste water must remain in the ATU for a length of time calculated by the system designer. Common controls consist of electrical panels with timers that can run a pump as well as control the air blower or aerator. ATUs designed for nitrogen reduction, which requires the air supply to be temporarily shut off, benefit greatly from this set-up.

Fixed Film and Suspended Growth

Bacteria in an ATU that attaches to a medium is considered a fixed-film system. Media typically consist of plastic, textiles or gravel. These systems provide a consistent effluent quality because of their stable environment for bacteria to grow. ATUs that do not use a medium for bacterial growth are known as suspended growth units. These units grow bacteria in the mixed liquid portion of the tank. Suspended-growth ATU designs commonly require a separate area for solids to settle out.


For proper functioning of an ATU, the system must be properly maintained. Included with the design of the septic system is a management plan. Management plans include descriptions of the system, emergency contact phone numbers, timer panel dosing rates and general instructions. Maintenance includes pumping accumulated sludges from the tank, servicing of any filters and a visual inspection of plumbing and effluent quality. These steps prevent organic overloading and provide unobstructed air flow to the unit. Proper ongoing maintenance is vital to the proper functioning of aeration systems.

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