Herein, a radical innovation in biogas production is presented using a single-step membrane purification technology without any necessary pretreatment steps for contaminant removal and with the usage of low feed pressure. Asymmetric hollow fiber membranes with a thin, selective, non-porous layer made from polyester carbonate on the bore side were successfully used in a single-step raw biogas upgrading process at biogas plant Cholovice in the Czech Republic. A double-stage arrangement operated at 17 degrees C exhibited the best CO2/CH4 separation factor (beta similar to 23) with 96 vol% CH4 purity. This single-step biogas upgrading technology with highly H2S and water-resistant membrane modules allows reductions in capital expenditures of similar to 20% and in operational expenditures of 50% compared to high-pressure water scrubbing (HPWS) and similar to 70% compared to pressure swing adsorption (PSA). Due to the small energy consumption required merely for biogas compression, our units consumed around only similar to 2 MJ/Nm(3) CH4. Thus, our approach with significantly improved performance and robustness of the membrane separation process can be seen as a major breakthrough of membrane gas separation for inexpensive biogas production.