What is the difference between a conventional septic system and an aerobic system?

A conventional system is a septic tank plus a soil drainfield: solids settle in the tank and the liquid flows by gravity or pump into perforated pipes where the soil finishes treatment. Texas A&M AgriLife calls it the most cost-efficient choice where soils are suitable, but it does not work in clay without modification. An aerobic treatment unit (ATU) pumps air into the wastewater so oxygen-loving microbes break it down, producing much cleaner effluent that is often disinfected and sprayed on a lawn. EPA notes ATUs suit small lots, poor soils, high water tables and sites near water. The trade-off: ATUs need constant electricity and regular maintenance.

Sources

• Onsite Wastewater Treatment Systems: Septic Tank/Soil Absorption Field (L-5227)Texas A&M AgriLife Extension Service
• Onsite Wastewater Treatment Systems: Aerobic Treatment Unit (L-5302)Texas A&M AgriLife Extension Service
• Types of Septic SystemsU.S. Environmental Protection Agency