Method of and apparatus for digesting organic waste and/or sewage sludge

An improved method of continuously digesting material such as organic waste and/or sewage sludge, including the steps of feeding the material to be digested into the upper end of an enclosed space, withdrawing the material after being digested from the lower end of the enclosed space, aerating the material as it moves downwardly from the upper end to the lower end of the enclosed space, and adjustably supplying the air to the material as a function of values measured within the enclosed space, wherein the improvement comprises the steps of allowing the material to pass from the upper end of the enclosed space to the lower end thereof in a continuous body forming a single mass, finely distributing the total amount of air required for the digestion process of the material over the entire cross-sectional area of the lower end of the enclosed space so that the air supplied thereto contacts the entire cross-sectional area of the mass of material taken transverse to its direction of movement through the space as the air flows through said mass of material, in a direction opposite to the movement of the material through said enclosed space, adding a regulated amount of moisture to the air introduced into the enclosed space, withdrawing the air from the upper end of the enclosed space after its upward flow through the material, monitoring one of the CO.sub.2 and O.sub.2 content of the air withdrawn from the upper end of the closed space, comparing the actual value of the one of the CO.sub.2 and O.sub.2 content monitored with a predetermined desired value, regulating the flow of the air through the enclosed space based on the comparison of the desired and monitored values by separately controlling the introduction of air into the enclosed space and controlling the withdrawl of air therefrom thereby controlling pressure gradients in the various layers of said mass so as to adjust the oxygen level flowing through said mass in desired amounts, measuring the moisture content of the material in at least two locations spaced apart in the direction between the lower end and the upper end of the closed space, comparing the actual moisture content values with predetermined desired values, regulating the amount of finely divided water added into the air being supplied to the lower end of the enclosed space based on the comparison of the desired and measured values of moisture content, and heating the air supplied to the lower end of the enclosed space to a temperature in the range of 30.degree. to 50.degree. C.