A device for roasting spent activated carbon, waste sludges, or other organic wastes, includes a downdraft bed furnace, a first adsorber fluidly coupled to the furnace including a closed tank of adsorber process solution, a venturi scrubber and a cyclone separator coupled to the tank such that gases are sucked through the venturi and the cyclone separator, liquid effluents from the scrubber and separator falling by gravity into the tank, a second adsorber fluidly coupled to the first adsorber including a closed tank of adsorber liquid, a venturi scrubber and a cyclone separator coupled to the tank such that gases are sucked through the venturi and the cyclone separator, liquid effluents from the scrubber and separator falling by gravity into the tank, the second adsorber configured to remove impurities not removed in the first adsorber; and an exhaust blower fluidly coupled to the second adsorber unit and configured to pull air into the furnace and through the first and second adsorbers.