Reduced life cycle climate impact from manure through catalytic methane conversion and carbon dioxide removal.

Agri-food systems constitute around one-third of global greenhouse gas (GHG) emissions, with roughly half consisting of non-CO2 GHGs, mainly methane (CH4) and nitrous oxide (N2O). Methods and technologies to mitigate non-CO2 GHGs are currently limited, which is a reason for agriculture being categorised as a hard-to-abate sector. This study examines mitigation of GHG emissions from manure storage headspace through oxidisation of CH4 emissions at low concentrations, using a thermal catalytic process with and without subsequent CO2 capture and storage (CCS). The technology is studied using a combination of process modelling and life cycle assessment at four CH4 concentrations: 300, 1000, 3000 and 10,000 ppmv. The primary energy demand and net climate effect were evaluated, reaching a net climate effect of +0.10, -0.77, -0.91 and -0.97 g CO2-eq emitted/g CO2 mitigated, respectively. The wide range of results is mainly influenced by the process energy demand being strongly correlated to the CH4 concentration. The sensitivity analysis shows that a net negative climate effect can also be achieved at 300 ppmv with access to low emission energy sources. Coupling CCS worsens the net climate effect of the system at all studied CH4 concentrations, mainly due to the additional energy demand for CO2 separation.