Abstract: A reaction vessel for biologically decomposing a material comprises a frame, an airtight housing rotatably mounted on the frame defining an enclosure therein, and a device for controlling environmental conditions within the enclosure so that biological decomposition of the material can occur at a controlled rate. Air is circulated through the enclosure in a closed loop so that air leaving the enclosure will be recirculated back into the enclosure. A computer controls the oxygen level of the air inside the enclosure, the humidity of the air inside the enclosure, the temperature of the air inside the enclosure, and the carbon dioxide level of the air inside the enclosure. The housing is disposed at an incline relative to the frame so that the material introduced into the enclosure proximal to the higher portion of the housing tends to flow toward the lower portion of the housing. A separating wall is disposed within the enclosure, forming therein a first chamber and a second chamber.