There are various biomethane upgrading technologies available on the market, based on different chemical and physical principles relating to gas separation. AB has chosen the membrane-based system, the most widely used worldwide, consisting of special polymeric materials with a selective permeability useful in separating CH4 and CO2. The pretreated gas is compressed over several phases and sent to different stages of membranes to optimize the operation; two stages aligned in series ensure compliance with grid specifications, while a third stage has the specific task of optimizing methane recovery while simultaneously limiting emissions into the atmosphere. Through independent compressions management the control system is able to regulate the operating pressures in the separation stages, thus ensuring the required performance with the lowest possible energy consumption. Other advantages are the simplicity of the process (without intermediate phases or the use of chemicals or consumables) along with high scalability and flexibility – e.g. operation also with partial loads (ideal for possible future plant expansion).