Abstract: The wastewater treatment method of the present invention includes introducing an influent water to an oxygen-supply tank for aeration; introducing the oxygen-enriched water from the oxygen-supply tank into the bottom of an activated carbon tank, so that the oxygen-enriched water flows upward and expands the activated carbon bed. When the oxygen-enriched water flows through the activated carbon bed, the microorganisms on the activated carbon particles use the enhanced oxygen concentration to decompose the contaminants, such as COD, BOD, TKN, etc., that are contained in the water or adsorbed on the activated carbon particles. Most of the supernatant liquid in the activated carbon tank is recycled to the oxygen-supply tank for aeration, and a small amount of the liquid is discharged, thereby performing a suitable treatment on wastewater having various qualities by controlling the amount of oxygen supply in the oxygen-supply tank and the recycle ratio of (the oxygen-enriched water)/(the influent water).