Abstract: A process and apparatus for the treatment of flowable waste in a waste treatment reactor and in particular the treatment of waste water in a bioreactor containing a bed of support particles having an attached biofilm and entrapped microorganisms are described. The process includes the steps of intermittently introducing waste water through a discharge port adjacent a bottom surface of the bed to form a series of plugs of waste water integrated with the microorganisms in the immediate vicinity of the discharge port; and maintaining a quiescent period following each introduction of waste water to promote biological degradation of contaminants in the waste water of each plug by the microorganisms and production of treated waste water.