"Upgrading of Biomethane Production In An Inclined Plug-Flow Type Anaerobic Digestor Fed With Biomass And Agroresidues"

At ENEA-Trisaia research centre an inclined plug-flow type anaerobic digestor was coupled with an upgrading section consisting in a polymeric membrane, for biomethane production. The biogas produced by biomass and agroresidues fermentation is a mixture of different gases such as methane, carbon dioxide, hydrogen sulphide, nitrogen, hydrogen, mercaptans and oxygen. Low-pressure biogas membrane upgrading tests showed that at a pressure < 1 MPa biomethane recovery is over 50% (with a purity of about 70% v/v). High-pressure biogas membrane upgrading tests showed that at a pressure close to 3.0 MPa, it is possible to obtain a high purity biomethane stream with a CH4 concentration of about 99.5% v/v, but with a recovery of about 20% and CO2 selectivity < 1. A secondary membrane separation stage is required to overcome this problem allowing for an increased biomethane recovery keeping the purity unchanged. On this aspect further research work is necessary.