Method for the treatment of complex waste

A method for treating a mixture M1 comprising at least organic matter, the method comprising:

• a) pressurizing the mixture M1 at a pressure of 150 to 300 bar to obtain a mixture M1p
• b) heating the mixture M1p at a temperature ranging from 250° C. to 500° C. to obtain a mixture M2;
• c) separating mixture M2 from step b) in order to obtain a stream M3 enriched in inorganic matter and a stream M4 depleted of inorganic matter;
• d) carrying out hydrothermal gasification on stream M4 depleted of inorganic matter to obtain a mixture M5 comprising gas and a liquid effluent;
• e) cooling and separating at least one fraction of mixture M5 resulting from the hydrothermal gasification of step d) in order to separate the gas from the liquid effluent M5′ comprising ammonia;
• f) optionally enriching at least one fraction of liquid effluent M5′ in ammonia to obtain an ammonia-enriched stream M5″ and an ammonia-depleted stream M8;
• g) mixing (i) at least one fraction of the inorganic-matter-enriched stream M3 obtained from step c) and (ii) at least one fraction of the liquid effluent M5′ or at least one fraction of the enriched stream M5″ resulting from step f) when it is present, to obtain a mixture M6;
• h) forming struvite from at least one fraction of mixture M6 in a precipitation reactor;
• and
• i) recovering struvite at an outlet of the precipitation reactor,
• wherein the method further comprises injecting at least one magnesium salt into the mixture M1 before step a) and/or during step g) and/or during step h) and/or into the mixture M6 between steps g) and h).