TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Method: The treated waste is classified through a screen to remove fraction having size of less than 10 mm. The fraction having size of less than 12 mm or less than 10 mm contains less than 1 wt.% of plastic. The fibrous fraction is treated to yield a fraction with less than 1 wt.% of inorganic material. The fibrous content is dried to 55 wt.% or less of moisture. The gas emitted during the application of the vacuum is treated with a fluid to clean the exhaust gas from solid and volatile contaminants during usage of vacuum pump to achieve a vacuum of 0.8 bar or less. Two or more vessels are used alternately. The vacuum pump is an eccentric-rotary vacuum pump, and has capacity sufficient to reach vacuum of 0.5 bar in a vessel having volume of 10 m3 or more in 15 minutes or less. The exhaust gas is cleaned in a scrubber. The fluid used to clean the exhaust gas is process water, which is used in portion to wet waste, which is fed to the vessel. The vacuum is applied after charging of vessel and before adding steam. The solid waste is treated in two or more vessels, which are used alternately. The vessel is depressurized, and steam is transferred from primary vessel to secondary vessel with the aid of a compressor, which is steam driven compressor. The content of vessel is heated through indirect heating with thermal fluid. The thermal fluid is provided via a heating system comprising a primary circuit with a heating element, and secondary circuit for heating two or more vessels independently. Indirect heating is applied through conduits in the vessel, and through a heated jacket. The inner surface and the coils of the vessel are at 100 degrees C or less during discharge of the vessel. The municipal waste is treated in an autoclave process, and classified. The open side of conveyers and other open equipment in the classification section after autoclaving comprise a hood with air suction to catch dust and volatile material. Air stream is supplied to a washing or cleaning section. The velocity of inward air stream of air suction is 0.1 m/second or more. Steam (more than 90%) used for the direct steam injection is derived from another pressure vessel used to treat waste. The average energy input is 125 kWh or less per ton of waste. The amount of energy supplied during normal operation through boiler steam is 25% or less, preferably 10% or less. The vessel is designed such that 35-80% of energy is transferred through jacket, and 20-65% of the energy is transferred through the internal conduits. The conduits are assembled such that they act as baffles to stir the content of the vessel. The vessel is insulated on the outside of the vessel. Municipal waste is treated in an autoclave process, and treated material is classified. The fiber product contaminated with glass and grit particles is subjected to an air separation step on a vibrating screen, which causes the lighter particles to flow downward, and the heavier particles to move upwards.