The unique AGAR attached growth aeration system supplies process oxygen that circulates thousands of special carriers through a reactor, creating an enormous total surface area for biofilm growth. This biological treatment process is easily retrofitted into existing wastewater plants, doubling the tank capacities, and enables upgrading to a complete BNR system using integrated fixed-film activated sludge (IFAS) processes, such as with existing lagoon treatment. The result is an enhanced wastewater treatment process without an expanded footprint.