apparatus for high - efficiency drying of material includes a vacuum drying chamber maintained at a low pressure by a vacuum pump . material to be dried is introduced to the drying chamber through an air lock valve and is transported through the drying chamber by an auger . in the preferred embodiment a second interconnected drying chamber includes a further auger , and material that has been dried is removed from the drying chamber by another air lock valve . microwave energy sources apply energy to vaporize liquid from the material , and air inlets are provided at the processed ends to introduce air for sweeping generally across the material to the outlet to the vacuum pump . the sweep of cool air causes an aerosol mixture to form , which is removed by the vacuum pump . heat is reclaimed by separating liquid and vapor , with the liquid being passed through hollow shafts of the augers to heat the material in the drying chamber , and the vapor being sent through a heat exchanger in thermal contact with a preheat zone so that heat from the vapor removed from the drying chamber , including latent heat of vaporization , is transferred to the material prior to introduction to the drying chamber .