TECHNOLOGY FOCUS - ENVIRONMENT - Preferred Process: The steam transfer from one autoclave to another autoclave is aided by at least one thermocompressor. The temperature during the cooking cycle is greater than or equal to 121 degrees C, preferably greater than or equal to 140 degrees C. In the process, the autoclave is initially filled for greater than or equal to 75 vol.%, preferably greater than or equal to 90 vol%, and greater than or equal to 25% of the energy content is swapped from the first to the second vessel. The process comprises: (a) optionally, pre-treating material to improve its properties; (b) feeding material into an autoclave (pressure vessel); (c) agitating the autoclave while creating a steam atmosphere at elevated pressure in the autoclave by applying steam (and optionally heat) to the contents of the autoclave, (cooking cycle) to change the properties of the contents; (d) cooling and/or depressurizing the autoclave; (e) discharging the autoclave; (f) classifying the treated waste to yield several fractions e.g. fibrous fraction, shattered glass and grit fraction and fraction with larger parts e.g. plastics and metals; and (g) optionally, further separation and/or improvement of the fractions, where during step (c), at least part of the steam and gas atmosphere is purged to a condenser, and further steam is fed into an autoclave vessel, and during step (d) at least part of the steam is transferred to another vessel, which is in an initial phase of step (c). The purging is effected for at least four times during the cooking cycle, where the purging is effected (semi) continuously. The gasses from the autoclave are purged to a scrubber or condenser to lower the content of volatile organic compounds and/or inerts in the gaseous phase. The gasses emitted from the condenser/scrubber are further treated in a biofilter. In step (c), the vessel is agitated while having steam pressure at 2.5-8 bar abs, and at 127-170 degrees C for at least 15 minute, where after step (b), steam at greater than or equal to 165 degrees C and a pressure of greater than or equal to 5 bar (abs), but where the pressure is at least greater than or equal to 2 bar than the required pressure during the cooking cycle, is injected into the vessel after closing to raise the pressure within the vessel to 2.5-8 bar (abs) in condensing atmosphere, and then in step (c), preferably for a suitable period, continuing to inject steam at a reduced flow rate to allow heating of the waste material by steam condensation and to maintain the waste treatment conditions. The steam transfer from the autoclave vessel to the accumulator is aided by the thermocompressor. EXAMPLE - No suitable example given.