Extended Aeration is a type of activated sludge process with no primary settling and very long aerobic detention time to generate less excess sludge overall. It is ideal for smaller flow, modular applications that require low maintenance, such as residential subdivisions. But the long HRT of Extended Aeration means larger basins, and when capacity growth outpaces available space, IFAS can be a good solution.

Additionally, if stricter regulations require nutrient removal, IFAS can help convert an Extended Aeration process into a staged Biological Nutrient Removal system.