Abstract: A system for the treatment of waste water including hydrocarbons and of a high biological oxygen demand. Preferably, the system includes a portable platform suitable for transport from site to site. A reaction vessel defining a substantially vertically oriented flow path therethrough for flowable waste water is mounted with its lower portion within and surrounded by a collection basin which receives waste water for treatment and recycling via trickling down through a biomass disposed on packing material within the reaction vessel. Simultaneously with the trickle down of the waste water, ambient air is forced upwardly countercurrent to the flow of the waste water to provide oxygen to the biomass, to enhance the flow of waste water over the biomass, and to sweep gaseous products from the reaction vessel. Optionally, oxygen is introduced into the collection basin to enhance biodegradation reactions within the collection basin. The system may be operated in either batch mode or continuously.