Low vacuum thermochemical conversion of anaerobically digested swine solids

• Biochar samples from digested swine solids were produced using hot stage in ESEM.
• Pyrolysis temperature rate under low vacuum (0.13 kPa) was set to 20 °C min−1.
• Six low vacuum peak pyrolysis temperatures between 300 and 1000 °C were assessed.
• As low vacuum peak pyrolysis temperature rises, the mineral fraction increases.
• Nitrous oxide emissions exponentially increase up to 1000 °C.

This work provides data on the production of biochar from the pyrolysis of the solid phase of swine effluents following anaerobic biodigestion. The study involved the low vacuum thermochemical conversion by environmental scanning electron microscope (ESEM) in a thermoregulated hot-stage tungsten SEM. The feedstock was characterized by FTIR, ESEM and energy dispersive X-ray analysis (EDS). The charred feedstock at peak temperatures of 300 °C, 400 °C, 500 °C, 600 °C, 700 °C, and 1000 °C were assessed by SEM and EDS. For each pyrolysis experiment, the exhaust gases were monitored by photoacoustic spectroscopy. SEM/EDS indicated that for increasing peak temperature in low vacuum pyrolysis, the mass losses are greater and the proportion of mineral particles such as P, Ca and Mg in the biochar. Photoacoustic spectroscopy showed that low vacuum pyrolysis is responsible for emissions of toxic gases NH3 and SO2 and radiative trace gases, especially N2O above 600 °C.