Abstract: A process and apparatus for the treatment of waste water utilizing a downflow or upflow system incorporating a suitable media or biological growth wherein air is sparged into the media on an intermittent or pulsed flow basis at selected time intervals and the pulsed application of air allows the trapping of the air bubbles in the media bed based at least in part on particulate media size, shape and biofilm growth and thereby provides a more significant avenue of oxygen transfer due to a prolonged exposure of the air bubbles with the biomass and the absorption of oxygen directly from the film of the bubbles to the biofilm in addition to transfer from surrounding liquid due only to oxygen diffusion.