Apparatus for integrated biological wastewater treatment and clarification including a tank having a wastewater inlet for receiving wastewater to be treated and having a treated, clarified wastewater outlet for providing treated, clarified wastewater for use, the tank having an upper turbulence region, a lower solids settling region below the upper turbulence region and a sludge collection region below the lower solids settling region, a multiplicity of biomass carriers disposed in the upper turbulence region, a gas diffuser assembly arranged generally between the upper turbulence region and the lower solids settling region for providing gas bubbles which move upwardly through the wastewater and the biomass carriers in the upper turbulence region, providing turbulence and oxygen and a sludge removal conduit communicating with the sludge collection region for removal of sludge therefrom.