Carbon capture technology is often associated with ideas of capturing CO₂ from power plants or industrial facilities like cement plants. Biomethane upgraders provide CO₂ that is easy to capture and less controversial than most other potential sources for CCS and also CCU. Yet, they are rarely part of the discussion.
In summary, it’s same CCS with a different CO_2 source, biogas. No CO_2 is removed from the atmosphere; gas which would otherwise by released can be capture. The paper discusses that capturing from biogas upgraders is more efficient than capturing from other sources. They not discuss the actual capture-and-storage process.