The development of methanisation sectors is part of a drive to create a circular economy that simultaneously serves three purposes:
- treat waste,
- supply energy (biogasa),
- and produce fertilizers (digestates).
Biogas can then be purified to form biomethane, which is then injected into the mains gas network.
As a supplement to natural gas imports, this regional production of biomethane is a potential lever for the energy transition.
As part of a project aimed at recycling livestock farming waste and biowaste produced in the same area, IFPEN has carried out Life Cycle Assessments (LCA) to simultaneously compare the environmental impacts of “waste treatment” and “energy supply” services, in the presence or absence of a methanisation sector(1):
- without the sector: storage and spreading of livestock manure, landfilling and/or composting of biowaste, energy supply by natural gas combustion;
- with the sector: anaerobic digestion of biowaste and livestock manure, combustion of the biomethane produced and recycling of digestates.
This study underlines the fact that methanisation enables — for the same amount of energy produced — a significant reduction in greenhouse gas (GHG) emissions, thanks to the combination of services provided: approximately 180 kg of CO2 equivalentb less per ton of waste, half of which is due to their treatment and the other half to the energy supply.
Furthermore, the CO2 produced by biogas purification can be recycled using a methanation processc.
Analysis of coupling of the two processes highlights the impact on the overall performance of the electricity mix composition used to produce the hydrogen required, via water electrolysis(2).
This territorial methanisation approach could be compared with the anaerobic digestion of dedicated crops (like in Germany), with the latter not providing any “waste treatment” service.
a- Biogas is composed of methane (CH4), CO2 and impurities.
b- Since all GHG emissions share CO2 as a common unit, the term CO2 equivalent is used for all of them.
c- Power to Methane: industrial methane production process via catalytic conversion of dihydrogen (H2) and carbon monoxide (CO) or carbon dioxide (CO2).
(1) A. Bouter, Life Cycle Assessment of territorial biogas production by anaerobic digestion of local wastes - SETAC Europe 25th Annual Meeting 2015 (Ref. MO400: page 235 in the Abstract Book)
(2) P. Collet, E. Flottes, A. Favre, L. Raynal, H. Pierre, S. Capela, C. Peregrina, Techno-economic and Life Cycle Assessment of methane production via biogas upgrading and power to gas technology - Applied Energy, 2016, 192, 282-295.
>> DOI: 10.1016/j.apenergy.2016.08.181