NOVELTY - Operating a biogas system (1) based on dry fermentation principle comprising a number of biogas fermenters that are run in batch mode, comprises (i) loading at least one of the biogas fermenters with fresh biomass and maintaining the other biogas fermenter which produces highly concentrated biogas; (ii) providing closure of at least one biogas fermenter loaded with fresh biomass; (iii) connecting at least one biogas fermenter to at least one of the other biogas fermenter; (iv) returning the biogas mixture; (v) terminating the return of the biogas mixture.    USE - The method is useful for operating a biogas system.    ADVANTAGE - The method: is carried out in batch mode; utilizes structurally simple device; and ensures continuous delivery of biogas.    DETAILED DESCRIPTION - Operating a biogas system (1) based on dry fermentation principle comprising a number of biogas fermenters that are run in batch mode, comprises (i) loading at least one of the biogas fermenters with fresh biomass and maintaining the other biogas fermenter which produces highly concentrated biogas; (ii) providing closure of at least one biogas fermenter loaded with fresh biomass; (iii) connecting at least one biogas fermenter loaded with fresh biomass to at least one of the other biogas fermenter which produces biogas; (iv) returning the biogas mixture from at least one freshly loaded biogas fermenter to at least one of the other biogas fermenter; (v) terminating the return of the biogas mixture from the freshly loaded biogas fermenter after a defined time duration. An INDEPENDENT CLAIM is also included for a biogas system operated based on dry fermentation principle, comprising biogas fermenter having a biogas outlet and a gas inlet, where the biogas outlet of at least one biogas digester is connected with the inlet of other biogas fermenter for a specific period of time by a gas return line and valve device (12).    DESCRIPTION OF DRAWING(S) - The figure shows a schematic top view of the biogas system with many biogas fermenters (Drawing includes non-English language text).    Biogas system (1)    Gas collection line (6)    Control device (7)    Valve device (12)    Gas recirculation line (14)