Biofuel Production as an Example of Virtuous Valorization of Swine Manure

The recovery of energy from organic waste opens a chance to promote the renewable energy production, reducing the use of fossil-based fuels. This study is focused on the virtuous valorization of swine manure, which is conventionally used as a fertilizer. An integrated valorization process of swine manure via transesterification and CO2-assisted pyrolysis was suggested to maximize the recovery of energy-intensive and value-added products, such as biodiesel, biochar, and syngas. Lipid fraction in the swine manure was transformed into biodiesel through thermally induced transesterification. The yield of biodiesel was ≥94 wt % (based on the lipid content) in the existence of silica and swine manure biochar at 400 and 220 °C, respectively. The biochar acted as a porous medium and alkaline catalyst for transesterification. The residual solid after transesterification (i.e., lipid-extracted swine manure) was valorized with pyrolysis. CO2 was fed as a co-reactant to carry out the process in a more sustainable manner. In the presence of CO2, the enhancement of CO production was observed because of the homogeneous reactions of CO2 with gaseous pyrogenic products derived from swine manure, compared to pyrolysis in a N2 atmosphere. To expedite the reaction rates affecting the homogeneous reaction, a Ni/SiO2 catalyst was adopted. Syngas formations were significantly enhanced through the synergistic effects of CO2 and the Ni/SiO2 catalyst. All experimental observations signified that swine manure could be considered a useful resource that can be valorized into value-added fuels and chemicals.