What Is Septic Tank Aeration?

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In rural and suburban areas where homes are not connected to public sewer systems, on-site septic systems treat waste water before returning it to the environment. Traditionally, underground septic tanks were anaerobic, meaning that they functioned in the relative absence of oxygen. Many homeowners today use aerobic septic treatment.

Septic Aeration

An underground septic tank is filled with oxygen through aeration. This process must happen continuously for aerobic septic systems to function. A mechanism called an aerator pumps air into the septic tank from outside. This enables a septic tank to support aerobic bacteria that break down pollutants in waste water and consume and remove harmful bacteria and viruses.

Aerobic Bacteria

Aerobic bacterial colonies can more fully treat waste water than anaerobic bacteria. According to the Food and Agriculture Organization of the United Nations, aerobic bacteria are also less susceptible to household chemicals. However, aerobic bacteria have more difficulty breaking down inorganic solids, so aerobic systems can clog more easily. Because aerobic bacteria require constant aeration, lengthy power outages can temporarily hinder the proper functioning of aerated septic systems.


Aeration tends to make septic systems more expensive to maintain than traditional anaerobic septic systems. Because the aerator is susceptible to mechanical malfunction, aerobic systems typically require more frequent routine maintenance. Aeration requires electricity, so maintaining aerobic bacterial colonies also increases the monthly electricity bill.

Aeration and Drain Field Size

Most septic systems have drain fields to receive waste water from the septic tank for even distribution to the soil, where it is treated further. Because aerobic bacteria can more fully treat waste water, aerobic septic systems usually require smaller drain fields than anaerobic systems. Aeration makes septic treatment possible in cases where a homeowner has little space or when the soil type is not ideal for treating large volumes of waste water.

Stand-Alone Tanks

In some cases, aeration enables a septic tank to treat waste water so effectively that it does not require a drain field. The effluent from stand-alone septic tanks can be safely used to water a lawn or can otherwise be released back into groundwater. Stand-alone tanks save space and help homeowners avoid the costly repairs associated with underground drain fields.

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