On the strong exothermicity of fecal matter pyrolysis under an inert atmosphere

Understanding the role of the exothermic pyrolysis is important for the design of reactors and gasifiers that seek to convert or even destroy fecal matter. In the present work, we reveal clear experimental evidence of fecal matter exothermic pyrolysis from human, pig, and chicken, under the conditions of differential scanning calorimetry. The results suggested that the strong exothermicity is related to the presence of inorganic elements in feces, Fe, Cu, Si, Pb, and Al, catalyzing the exothermic reactions, such as the partial fixed carbon oxidation and the inorganic reduction reactions. The pig feces presented the highest inorganic content, and the lowest fixed carbon content, 4.21 wt%. For all samples, the exothermicity of pyrolysis overcame endothermic reactions, leading to a maximum positive balance of 631.84 J/g. The pyrolysis efficiency reached values up to 10%. Based on the experimental evidence, a conceptual mechanism leading to exothermicity was drew for heterogeneous and homogeneous exothermic reactions affecting positively the overall energy balance of pyrolysis.