A system for wastewater treatment comprises a tank and includes a mixer that generates large mixing bubbles, for example a bubble having a largest dimension of 6 inches to 10 feet. In some embodiments, the mixer is located in the anoxic zone. The mixing bubbles are large enough to move wastewater as they rise to the surface and generate a mixing current in the wastewater. The mixing current mixes the wastewater, and bacteria and other microorganisms to promote the bacteria and other microorganisms' conversion of the pollutants contained in the wastewater. The system further comprises an Integrated Fixed-film Activating Sludge (IFAS) system.