This study developed a membrane separation process for biogas using a DDR-type Zeolite membrane with high CO(2)/CH(4) selectivity. Biogas produced in a sewage plant was separated and purified by using the DDR-type Zeolite membrane, and the performance and durability of the membrane was estimated. We first analyzed the membrane performance required for a simple, one-stage separation process through a mathematical model and experimentation, and then decided upon the appropriate flow rate through DDR. type Zeolite pattern usage. Next, in order to conduct actual biogas separation and purification, we set up a pilot plant within the sewage treatment facility. The purification tests showed that purification was possible with our objective purity of CH(4) concentration of 90% and emission CO(2) concentration of over 97%. Separation factor of CO(2)/CH(4) and permeation of the DDR-type Zeolite membrane changed little even after 40 h of ventilation. These results demonstrate that the membrane separation process developed is fully applicable to the separation and purification of biogas. Finally, we examined the influence of impurities in the biogas on membrane separation performance by supplying the biogas without pre-treatment for 1600 h. From the results, we believe that membrane performance is reduced by long periods of ventilation and high boiling compounds such as higher hydrocarbons and siloxane, which are present as impurities in the biogas.