Device for biologically transforming pyrogasification gas into biogas (19, 23) comprising: - a liquid digestate production unit, comprising a raw digestate production unit and a phase separation system, with the joint function of producing liquid digestate containing anaerobic bacteria, - an RLMB functional unit comprising four functions: (i) a cooling function R of the pyrogasification gas, (ii) a washing function L of the pyrogasification gas, (iii) a methanisation function M of at least a portion of the by-products of the pyrogasification gas SPGP, extracted from the pyrogasification gas by the cooling function R and washing function L, so as to form biogas, (iv) a biomethanation function B of the syngas, extracted from the pyrogasification gas and separated from the by-products of the pyrogasification gas SPGP by the cooling function R and washing function L, so as to form biogas, the RLMB functional unit being supplied by at least the pyrogasification gas, and by digestate originating wholly or partly from the liquid digestate production unit, the RLMB functional unit comprising one or more separate sub-units each capable of performing all or some of one or more of the cooling, washing, methanisation and/or biomethanation functions. - a liquid digestate production unit, comprising a raw digestate production unit and a phase separation system, with the joint function of producing liquid digestate containing anaerobic bacteria, - an RLMB functional unit comprising four functions: (i) a cooling function R of the pyrogasification gas, (ii) a washing function L of the pyrogasification gas, (iii) a methanisation function M of at least a portion of the by-products of the pyrogasification gas SPGP, extracted from the pyrogasification gas by the cooling function R and washing function L, so as to form biogas, (iv) a biomethanation function B of the syngas, extracted from the pyrogasification gas and separated from the by-products of the pyrogasification gas SPGP by the cooling function R and washing function L, so as to form biogas, the RLMB functional unit being supplied by at least the pyrogasification gas, and by digestate originating wholly or partly from the liquid digestate production unit, the RLMB functional unit comprising one or more separate sub-units each capable of performing all or some of one or more of the cooling, washing, methanisation and/or biomethanation functions. (i) a cooling function R of the pyrogasification gas, (ii) a washing function L of the pyrogasification gas, (iii) a methanisation function M of at least a portion of the by-products of the pyrogasification gas SPGP, extracted from the pyrogasification gas by the cooling function R and washing function L, so as to form biogas, (iv) a biomethanation function B of the syngas, extracted from the pyrogasification gas and separated from the by-products of the pyrogasification gas SPGP by the cooling function R and washing function L, so as to form biogas, the RLMB functional unit being supplied by at least the pyrogasification gas, and by digestate originating wholly or partly from the liquid digestate production unit, the RLMB functional unit comprising one or more separate sub-units each capable of performing all or some of one or more of the cooling, washing, methanisation and/or biomethanation functions. the RLMB functional unit being supplied by at least the pyrogasification gas, and by digestate originating wholly or partly from the liquid digestate production unit, the RLMB functional unit comprising one or more separate sub-units each capable of performing all or some of one or more of the cooling, washing, methanisation and/or biomethanation functions.