Abstract: The invention provides a method and apparatus for increasing the rate of aerobic digestion of an organic waste. The apparatus is particularly suited for use with commercial or residential septic tanks. In general, the apparatus includes a medium with high surface area to volume ratio, a portion of which extends above the liquid level of waste in the tank. Aerated waste is frothed upward above the medium and cascades down over the exposed medium thereby enhancing aeration and subsequent reduction of biological oxygen demand concentrations. In certain embodiments the apparatus includes a surrounding clarifier to remove floating scum. The concentration of biological oxygen demand in the effluent from a septic tank may be reduced from about 230 mg/l to less than about 40 mg/l, and the total suspended solids concentration can be reduced from 75-150 mg/l to about 10 mg/l by using the apparatus and method of the invention.