*9.1.3 Minimization of CO2 footprint*

Circular bioeconomy could decarbonize energy systems and reduce CO2 footprint. Substituting Haber-Bosch fertilizer with digestate for example avoids the 7 tons of CO2 emitted for each ton of fertilizer produced. Studies replaced fossil fuel with biogas in the transport sector. Biogas caused only 21–36% of the GHG emissions of fossilbased fuels [162], and biomethane reduced CO2 footprint by 49–84% [163]. Emissions linked to AD production of renewable energy and biofertilizer were lower than those for production of fossil energy and mineral fertilizer [164]. A study of combined heat and power (CHP) production found that pressurized AD systems achieved a direct CO2 footprint of about 13 kgCO2/MW hf. This footprint is quite low when compared to the 700 kgCO2/MW hel direct CO2 footprint of conventional CHP systems [165]. In the analysis of sorghum cultivation as an energy crop, inorganic fertilizer accounted for 51% of GHG emissions; digestate decreased carbon footprint by 11%. Digestate was then recommended for sustainable energy crop production and GHG mitigation [166]. Furthermore, a study from Switzerland quantified their national biomass availability and confirmed its potential for biofertilizer provision and climate change mitigation. The authors concluded that by 2050, circular bioeconomy application of AD would save significant amounts of mineral fertilizer (over 10 kt/a), and GHG emissions (38 kt/a of CO2eq) [167].
