The present invention provides a method for processing wastes containing a large amount of water and a method for processing leachate from industrial wastes. Specifically, the present invention provides a method which comprises maintaining reduced pressure in the dryer equipped with a stirring means, feeding wastes containing a large amount of water to the dryer, stirring the wastes while blowing refrigerated air at -20.degree. C..+-.5.degree. C. to the dryer, and drying the frozen moisture portion of the wastes by sublimation. Air heated at 80.degree. C.+10.degree. C. can be used instead of refrigerated air to dry water of the wastes by evaporation. The present invention also provides a method for processing leachate which comprises pooling leachate industrial wastes and burned ashes, and utilizing the leachate to absorb wet-type toxic gas, thereby confining the leachate within the waste treatment plant. The present invention therefore make it possible to process wastes containing a large amount of water, which have been a problem in the incineration by the conventional methods, by using the potential heat of the waste gas from the incinerator. The present invention also provides an effective means to prevent environmental contamination because leachate is confined in the waste treatment plant.