TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Concentration: The amount of sludge in the biomass is 40-65 (preferably 50-60) wt. %. The amount of green waste in the composting mixture is 10-35 (preferably 15-30) wt. %. The amount of sand in the biomass is 10-30 (preferably 15-25) wt. %. The content of water in the sludge being fed into the mixer is 85-70 wt. %. The content of water in the sand being fed into the mixer is less than or equal to10 (preferably less than or equal to5) wt. %. The amounts of sludge, sand and green waste and the content of water in the sludge, sand and green waste are selected to obtain a biomass having water content of 40-65 (preferably 50-60) wt. %.Preferred Property: A major part of the particles of the sand being fed into the mixer have no dimensions larger than 10 (preferably larger than 4) mm. A major part of the particles of the green waste being fed into the mixer have no dimensions larger than 50 (preferably larger than 20) mm. A major part of the particles of the green waste being fed into the mixer have no dimensions larger than 8 (preferably larger than 4) mm.Preferred Parameter: The composting step comprises a hygienic treatment having a heating step during which the biomass is heated to a temperature of greater than or equal to70 degreesC for greater than or equal to1 hour. The biomass is heater to a temperature less than or equal to80 degreesC for greater than or equal to1 hour.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Concentration: The amount of sludge in the biomass is 40-65 (preferably 50-60) wt. %. The amount of green waste in the composting mixture is 10-35 (preferably 15-30) wt. %. The amount of sand in the biomass is 10-30 (preferably 15-25) wt. %. The content of water in the sludge being fed into the mixer is 85-70 wt. %. The content of water in the sand being fed into the mixer is less than or equal to10 (preferably less than or equal to5) wt. %. The amounts of sludge, sand and green waste and the content of water in the sludge, sand and green waste are selected to obtain a biomass having water content of 40-65 (preferably 50-60) wt. %.Preferred Property: A major part of the particles of the sand being fed into the mixer have no dimensions larger than 10 (preferably larger than 4) mm. A major part of the particles of the green waste being fed into the mixer have no dimensions larger than 50 (preferably larger than 20) mm. A major part of the particles of the green waste being fed into the mixer have no dimensions larger than 8 (preferably larger than 4) mm.Preferred Parameter: The composting step comprises a hygienic treatment having a heating step during which the biomass is heated to a temperature of greater than or equal to70 degreesC for greater than or equal to1 hour. The biomass is heater to a temperature less than or equal to80 degreesC for greater than or equal to1 hour.