An apparatus and a method for treating a composition containing toxic materials or biosolids, wherein the apparatus has a hydraulically sealable top that can be opened to allow loading of the composition or closed to seal the apparatus. The apparatus also includes a reagent injection system for injecting a reagent into the apparatus, a mixing device for mixing the composition with the reagent, a heater system for heating the composition, or the mixture of the composition and the reagent, an internal vapor recovery system for recovering gases, vapors, and odors from the toxic materials or biosolids, or from the reagents, a reagent recovery system for recovering the reagent after it has been mixed with the composition, a discharge mechanism for discharging the treated composition, and a control panel comprising temperature and pressure measurements.