In addition to the production of biomethane the Bright Biomethane systems may be used to recover and liquefy CO₂ to create an extra source of revenue for the owner of the biogas plant with biogas upgrading system. Zero methane slip is achieved since the small amount of methane still present in the CO₂ is recovered during the liquefaction process. When no liquid CO₂ production is required, the recovery system can be put in a stand-by mode that requires no additional energy.