To what extent can small-scale bio-CCS from biogas upgrading contribute with net-negative emissions?

Carbon capture and storage (CCS) of CO2 from biogas upgrading units has been proposed as a way to achieve negative CO2 emissions. This study evaluated the climate performance and energy efficiency of such a bio-CCS system from a life cycle perspective, encompassing management, transport and storage of the separated biogenic CO2. The results demonstrated a climate impact of 0.10 tonne CO2-eq emitted/tonne CO2 captured, corresponding to 90% carbon efficiency. Relative to biogas production, the emissions from the CCS value chain amounted to 3.9 g CO2-eq/MJ biomethane, with an energy demand of 0.056 MJ/MJ biomethane or 1450 MJ/ tonne captured CO2. On adding the benefit of stored carbon (-38 g CO2/MJ biomethane) to an emissions factor for Swedish biogas from bio-based waste, its value decreased to-15.4 CO2-eq/MJ biomethane. Sensitivity analyses highlighted the importance of utilising renewable energy sources, but also showed that a clear net-negative emissions balance can be achieved even under non-ideal circumstances, such as for long transport distances and fossil-based energy supply. These results indicate that coupling a CCS system to biogas upgrading has the potential to deliver net-negative greenhouse gas emissions, even with conservative assumptions regarding renewable energy availability and large transport distances relative to the small CO2 volumes mostly available from biogas systems.