Abstract: An improved process and apparatus for continuously treating sewage wastewater by chemical oxidation of the contaminates and characterized by a high degree of oxygen absorption and utilization. An enclosed vessel continuously receives liquid wastewater at one end thereof to define a liquid level and the treated sewage is continuously removed from the other end to maintain the liquid level. Oxygen gas in the form of a mixture of O.sub.2 and O.sub.3 is introduced under pressure into the vessel, while pressurizing the vessel and creating an oxygen-rich atmosphere in an upper portion of the vessel, to chemically treat the wastewater through absorption of the oxygen by the wastewater.