TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Apparatus: The apparatus (A1) comprises an oxygen level sensor (149) for giving a signal dependent upon the oxygen content of the gas in contact with the mixed solid waste, where the control unit is operable in response to the signal. The apparatus (A1) further comprises a sensor (150) for giving a signal dependent upon the moisture level of the gas in contact with the mixed solid waste during treatment, where the control unit is responsive to the signal. The apparatus (A2) further comprises units for gasifying the pyrolyzed mixed organic waste.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The solid mixed organic waste is treated in a rotary aerobic digester (116). The rotary aerobic digester is rotated at a rate of one revolution in a period of 1-10 (preferably 2-5) minutes. The organic waste and the other solid waste are mixed so that the overall average moisture level of the mixed solid waste before treatment is 45-60 wt.%. In the method, air is supplied to the treatment vessel by a forced draught or is supplied to the treatment vessel by a fan (148) drawing gas out of the treatment vessel. The air supplied to the treatment vessel has humidity below that of the ambient air. The moisture level of the gas in contact with the solid waste during treatment is controlled so that it does not exceed the dew point at the temperature in the treatment vessel. The waste is treated by aerobic digestion. The treated solid mixed organic waste is processed to form fuel or compost. After the pyrolysis process, the pyrolyzed waste is treated in a gasification process. The microbial activity is aerobic digestion. EXAMPLE - A process was operated with a feed comprising 75000 tons per annum of mixed municipal waste. The average moisture level of waste input to the rotary aerobic digester was 60 wt.%, with some batches having higher moisture level and some batches having lower moisture level. Treated waste collected from the rotary aerobic digester, after unloading and fan drying had a moisture level of about 30 wt.%. After 24 hours residence on the drying floor, the moisture level had dropped to below 15 wt.% and the product was stable. From an input of 75000 tones of combined waste materials, 40000 tones of Green Coal was produced having a calorific value equivalent to 15000 tones of fuel oil. The graded and pelletized product was found to have constant thermal characteristics and was suitable for use as a supplementary fuel. It had minimum calorific value of 14500 kJ/kg. It had an ash content of less than 20 wt.% and very small quantities of sulfur and chlorine.