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.