The present disclosure refers to a plant (1) for production of biogas (18). The plant (1) comprises a digester (4) including a bag-like casing (5) of flexible material and fluid-tight, wherein the bag-like casing (5) is adapted for the containing a sewage (14). The casing (5) defines, in an internal zone, a digestion chamber (40) adapted for a digestion of the sewage (14). The plant (1) further comprises a heater (45, 68) for heating the sewage (14). The disclosure further refers to a co-generation installation (100) comprising a plant (1) for the production of biogas (18), a co- generator (8) and fuelling means (71, 72) for fuelling the co-generator (8) with biogas (18), said fuelling means comprising a biogas line (71, 72) between the plant (1) and the co-generator (8).
