NOVELTY - The method comprises: subjecting a biomass mixed with water to an anaerobic fermentation in a first anaerobic fermenter (2) to obtain a concentrated liquid digestate and biogas (13A); pumping and grinding the liquid digestate by a pump/grinder to obtain a ground concentrate liquid digestate; separating fibers and particles of the ground liquid digestate to obtain a clarified water mixed with a balance of a comminuted liquid digestate and the concentrated wet ground digestate; and passing the clarified water mixed with a remainder of the ground liquid digestate in a water extractor (6).    USE - The method is useful for treating a biomass mixed with water in order to produce, independently, combustible solids, drinking water, biogas and struvite (all claimed).    ADVANTAGE - The method is capable of energy-efficiently treating the biomass mixed with water, thus improving the yield and purity of biogas and struvite.    DETAILED DESCRIPTION - The method comprises: (a) subjecting a biomass mixed with water to an anaerobic fermentation in a first anaerobic fermenter (2), which comprises two outlet conduits (3a, 3b) directly connected to the first anaerobic fermenter, to obtain a concentrated liquid digestate and biogas (13A); (b) pumping and grinding the concentrated liquid digestate by a pump/grinder to obtain a ground concentrate liquid digestate; (c) separating fibers and particles of the ground concentrate liquid digestate to obtain a clarified water mixed with a balance of a comminuted liquid digestate and the concentrated wet ground digestate, which passes into a lysis device; (d) passing the clarified water mixed with a remainder of the ground liquid digestate in a water extractor (6) to obtain drinking water and the balance of a comminuted liquid digestate, which pass into the lysis device; (e) obtaining a wet concentrate digestate ground and lysed from the lysed mixture of the remaining crushed liquid digestate with the ground concentrate digestate; (f) returning the wet ground and lysed concentrate digestate to the first anaerobic fermenter in a case of a device comprising a single anaerobic fermenter to produce the combustible solids and biogas, and a second-anaerobic fermenter in a case of device comprising two anaerobic fermenters comprising two outlet conduits directly connected to the second anaerobic fermenter and producing the combustible solids, a first portion of the biogas and a second portion of the biogas; and (g) dehydrating the combustible solids by a dewatering device (16), which receives the concentrate liquid digestate mixed with the concentrated wet ground and lysed digestate. The dewatering device is directly connected by a single outlet conduit to an outlet of the first anaerobic fermenter in the case of a device comprising a single anaerobic fermenter and directly connected by a single outlet conduit to an output of the second anaerobic fermenter in the case of a device comprising two anaerobic fermenters. The concentrated liquid digestate is mixed with the concentrate wet ground and lysed digestate in the anaerobic fermenters after re-injection of the concentrate wet milled and lysed digestate into the fermenters. The drinking water comprises no suspension material and has a dry matter content of strictly less than 1%. In the step (a), the concentrated liquid digestate rests at the bottom of the first anaerobic fermenter. In the step (b), the concentrate liquid digestate is pumped from the bottom of the first-anaerobic fermenter to the pump/grinder. A conduit is connected to the water extractor. The method further comprises a quality control step of extracted water using turbidity and conductivity, and a quality control step of biomass by the viscosity and rapid measurement of biodegradability. A conduit is connected to the first anaerobic fermenter. An INDEPENDENT CLAIM is included for a device for treating a biomass mixed with water in order to produce, independently, combustible solids, drinking water and biogas.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a device for treating a biomass.    First anaerobic fermenter (2)    Outlet conduits (3a, 3b)    Water extractor (6)    Biogas (13A)    Dewatering device. (16)