Aerobic systems are similar to septic systems in that they both use natural processes to treat wastewater. Unlike septic (anaerobic) treatment, the aerobic treatment process requires oxygen. Aerobic treatment units (ATUs), therefore, use a mechanism to inject and circulate air inside the treatment tank, which requires electricity to operate.
An aerobic treatment septic system is utilized in high clay content soils and/or also when water tables are near the ground surface. There are different disposal methods used with this type of system the most common and cheapest being surface spray. The next common disposal method is using drip irrigation tubing but the cost is higher for installation. Surface spray requires more land area so if you have a small piece of property, less than 1/2 an acre, with high clay content or signs of a seasonally high water table then drip irrigation disposal is the best option.
Limited use spray is occasionally utilized if necessary but is installed with the home owner understanding their daily water use may be somewhat restricted. If you overload the septic system with more water use than your spray field is designed for your yard will stay wet and if it is bad enough your effluent may runoff on to the neighbors property and you would soon find yourself dealing with the governing authority. The same can be said about drip irrigation disposal.
A typical aerobic treatment unit like the one shown above is designed to process 500 gallons per day of wastewater or up to a 4 bedroom home. Larger units are available for larger homes or when multiple homes are connected to a treatment unit.
Remember that the larger the home the larger the disposal field will have to be as well.