Biogas Holder for Anaerobic Digestion: Double-Membrane Gas Storage A biogas holder for anaerobic digestion waste is a gas storage system that captures methane at 5-30 mbar above a digester, smoothing supply to the generator or flare. The most common form is a double-membrane holder on a Glass-Fused-to-Steel (GFS) tank. Engineered by Shijiazhuang Zhengzhong Technology Co., Ltd. (Center Enamel) to AWWA D103-09 and ISO 28765, the membrane lasts 10-15 years. What a Biogas Holder