CO2 gasification of dairy and swine manure: A life cycle assessment approach

• Gasification of manure using CO2 as gasifying agent was studied by TGA-MS.
• Two CO2 manure gasification scenarios were evaluated by means of LCA approach.
• LCA included the economy, gas emissions and energy balance of manure gasification.
• The viability of manure gasification instead of its fertilizer use was verified.

CO2 gasification of three different chars obtained from the pyrolysis of two dairy manure samples and a swine manure sample was evaluated. Dairy samples were firstly pretreated by anaerobic digestion process and swine sample by bio-drying process. Subsequently, manure samples were pyrolyzed between 30 °C and 980 °C obtaining a solid fuel (biochar), which was later gasified using different vol.% CO2 (15–90%) which was the gasifying agent. Gasification was conducted at 900 °C. Thermal behavior and gasification characteristics were studied by means of the thermogravimetric-mass spectrometric analysis. In this sense, the reactivity of the samples was influenced by the catalytic activity of the mineral matter contained in the remaining biomass ashes. On the other hand, the viability of the manure gasification process vs the traditional use of manure as fertilizer was studied by means of the life cycle assessment (LCA) methodology. Two different scenarios were analyzed: gasification of manure sample before anaerobic digestion (Pre) and gasification of manure after anaerobic digestion (Dig R). According to the results obtained, the gasification of char Pre was the most viable scenario from the economic and environmental viewpoints whereas the gasification of char Dig R was the best energetic option.