This thesis explores the production of biogas from agricultural biomass and the strategic conversion of existing biogas plants to biomethane facilities, within the broader context of the energy transition and circular economy. It provides a comprehensive overview of the Italian agricultural biogas sector, with an emphasis on policy frameworks, regulatory incentives, and the role of the public authority Gestore dei Servizi Energetici (GSE). The core of the work focuses on the case study of the "La Falchetta" plant, originally designed for electricity generation through anaerobic digestion and currently undergoing reconversion to produce biomethane suitable for injection into the distribution gas grid.