TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Process: The urban solid waste, and/or the residue and/or scraps coming from agricultural and/or zootechnical activities, and/or the residue and/or scraps coming from the agricultural/food industry, and/or the residue and/or scraps coming from agricultural processes and/or from forestation and/or from silviculture, are treated by subjecting them to a preliminary grinding or sizesorting process before subjecting them to the liquefaction step (b). The liquefaction step (b) is carried out at 150-350 degrees C, preferably 250-320 degrees C. The liquefaction step (b) is carried out at a pressure of 5-170 bar, preferably 35-120 bar. The liquefaction step (b) is carried out for a time of 5-240 minutes, preferably 15-180 minutes. The oily phase, the solid phase and the aqueous phase included in the mixture obtained in the step (b) are separated by gravitational separation, filtering, centrifugation. Preferred Components: The sludge is primary sludge and/or biologic sludge produced in purification plants of civil and/or industrial wastewater. The sludge is used in a mixture with other materials such as: urban solid waste comprising organic material coming from the sorted waste collection and/or organic material from not sorted urban solid waste; or mixtures of the organic material with pruning cut-offs and/or agricultural residue; residue and/or scraps coming from agricultural and/or zootechnical activities; residue and/or scraps coming from the agricultural/food industry; residue and/or scraps coming from agricultural processes, from forestation and/or from silviculture; and/or oily by-products such as oils and/or fats, coming from the preliminary treatment of wastewater. The sludge is used in a mixture with oily by-products such as oils and/or fats, coming from the preliminary treatment of wastewater. EXAMPLE - Wet sludge (46,000 ton/year), oils and fats (282 ton/year) and sorted waste collection ( FORSU) (90000 ton/year) were continuously added to liquefaction, i.e. to a tubular reactor, at 310 degrees C (reactor inner temperature), a pressure of 110 bar (reactor inner pressure), for 1 hour. The reaction crude was separated, continuously, in a gravitational separator to obtain aqueous phase (i.e. second aqueous phase). The obtained aqueous phase (94300 ton/year) was sent directly to purification plant of urban wastewater and was turned out to be equal to 0.08 vol.%. The obtained solid phase comprising a solid residue (13,435 ton/year) was sent to a waste-to-energy plant to obtain oily phase containing bio-oil (24494 ton/year - equal to 500 barrels/day).