NOVELTY - Operating a biogas plant for solid organic wastes comprises: an anaerobic fermentation of organic paste load from municipal solid waste with the help of anaerobic bacteria; (b) a separation step to obtain a liquid fraction or leaching (FL) and a solid fraction (FS) of waste from the Digest or fermented organic paste; and (c) a feedback stage in order to replenish a settled fractional part (PFL) as anaerobic inoculum for the fermentation stage.    USE - The method is useful for operating a biogas plant for solid organic wastes (claimed).    DETAILED DESCRIPTION - Operating a biogas plant for solid organic wastes comprises: an anaerobic fermentation of organic paste load from municipal solid waste with the help of anaerobic bacteria; (b) a separation step to obtain a liquid fraction or leaching (FL) and a solid fraction (FS) of waste from the Digest or fermented organic paste; and (c) a feedback stage in order to replenish a settled fractional part (PFL) as anaerobic inoculum for the fermentation stage comprising: (i) a stage of storage and fermentation of a remainder of the liquid fraction (RFL) by methanogenic bacteria to methane gas production; (ii) a filtering stage residual liquid fermentation stage for further physical-chemical treatment of the liquid for use as liquid fertilizer; (iii) crushing of the solid fraction (FS) promptly treated which can be used as organic substituted or organic feed material; and (iv) a stage of drying the solid fraction (FS) in the outgoing phase separation by heat neutralization of the bacterial flora present in the solid fraction. An INDEPENDENT CLAIM is an installation to perform the procedure above comprising the installation (1): (a) a bioreactor (2) fed a load of organic paste from municipal solid waste for fermentation of the dough with the help of methanogenic bacteria; (b) a centrifugal separator (3) fed by the digested or organic paste from the bioreactor, for a liquid or leaching fraction (LF) and a solid fraction (FS) from the waste; and (c) a feedback loop (4) to replenish a portion of liquid (PFL) and methanogenic bacteria inoculum to the bioreactor, where the facility further comprises: (i) storage tanks (5) of the remaining liquid fraction (RFL); (ii) fermentation tanks (6) by methanogenic bacteria for methane gas obtained from the remaining liquid fraction of the storage tanks; (iii) filters (7) for filtering the liquid waste tanks for fermentation and subsequent physico-chemical treatment of the liquid for use as fertilizer liquid; (iv) a tank (8) for storage of residual liquid filtration; (v) an oven (9) for drying the solid fraction (FS) projection of the centrifugal separator for neutralization by heat of the bacterial flora present in the solid fraction; (vi) a shredder (10) for crushing the dry and solid fraction (FSS) promptly treated used as organic amendment and/or organic feed material; and (vii) an appropriate inerting device (12) for neutralization with N2 of the solid fraction (FS), and if necessary, a gasometer (13) for storage and subsequent use of the gas from the fermentation of the remaining liquid fraction obtained in the fermentation tanks (6).    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic diagram of the method for operating a biogas plant for solid organic wastes.