To inexpensively, stably and efficiently decompose environmental pollutants and malodorous substances over a long period of time by bringing a liquid or gas to be treated into contact with activated carbon substantially held to an aseptic state by heat treatment within a specific temp. range in the presence of an oxygen atom supply substance at specific temp.

The liquid to be treated in a tank 1 is sent to a mixing tank 3 by a liquid sending pump 2 and sent to an activated carbon packed column 6 from the mixing tank 3 by a circulating pump 4. The activated carbon packed column 6 is constituted by packing a stainless steel pipe with granular activated carbon 8 and arranging a heater 9 to the peripheral surface of the stainless steel pipe to heat the interior of the stainless steel pipe to the highest temp. of 100°C. An air supply apparatus 5 is disposed in the piping just before the liquid to be treated enters the column 6 and air is sent so that air bubbles enter the column 6 from the air supply apparatus 5. The liquid to be treated issuing from the column 6 is circulated so as to again enter the mixing tank 3 through the piping and the liquid overflowing the mixing tank 3 is discharged out of a discharge port 10.