A method and system for wastewater treatment includes flowing a quantity of a wastewater into a first microbubble chamber having a plurality of diffusers for injecting microbubbles into the wastewater to promote oxygenation. The microbubble includes activated sludge for treating the wastewater. The wastewater is then flowed from the first microbubble chamber through a plurality of rotating discs having a biofilm of microorganisms mounted thereon. The discs rotate about a shaft such that a portion of each disc is exposed to air during rotation. The wastewater is the flowed into a second microbubble chamber having a plurality of diffusers for injecting microbubbles into the wastewater. The treated wastewater is then recovered.