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Biomass carbon could be sequestrated in form of biochar, an aromatized carbon structure produced by pyrolysis. Inherent minerals are reactive constituents that interact with organic contents during pyrolysis, significantly affecting the properties of the pyrolysis product. Despite their importance, their influence on biochar-carbon sequestration has been rarely studied. This study selected four types of biomass: barley grass, peanut hull, cow manure and sewage sludge to investigate the influence of inherent minerals on carbon conversion during pyrolysis. Results showed removal of inherent minerals shifts the peak biomass conversion to a higher temperature (370 o C) compared to biomass with inherent minerals being present (330 o C). It also led to reduced emissions of low molecular weight organic compounds. Compared to pristine biomass, more carbon (3.5-30.1%) could be retained in biochar along pyrolysis after removing inherent minerals. And it showed increased resistance to chemical and thermal oxidation decomposition, indicating higher carbon stability and therefore carbon sequestration potential. Instrumental analysis showed removal of inherent minerals facilitated disappearance of oxygen-containing functional groups such as C=O, O=C-O and CO , while promoting C-C/C=C bonds, indicating higher aromatization of biochars. This study suggested that to remove minerals prior to pyrolysis can be a promising approach for strengthening carbon-sequestration potential of biochar.

Nitrogen (N) is one of the nutrients embedded in biowastes and its speciation in solid−liquid−gas pyrolysis products is closely related to environmental issues such as the greenhouse effect, acid rain, and eutrophication. This study investigated the distribution and evolution of N species during pyrolysis of various biowaste matrixes, and the roles of exogenous mineral calcium (CaCl 2 ) in regulating N transformation were explored. The results showed that these biowastes show a similar tendency for the conversion of protein-N (70−90% in biowaste) into char-N (25− 35%), oil-N (15−30%), and gas-N (30−60%). Exogenous Ca did not alter total char-N yield, while it promoted the conversion of protein/pyridine-N into pyrrole/quaternary-N, which could mitigate N loss as a cause of eutrophication; Ca catalyzed the cracking of N-containing macromolecules in bio-oil, especially amine, and therefore, drove N migrating from the liquid phase to gas phase. This would benefit the recycle of bio-oil as a fuel. In gas, the significant decrease of harmful HCN accompanied by a remarkable increase of NH 3 and N 2 were observed. Detection by thermogravimetric analysis− Fourier transform infrared spectrometry−gas chromatography mass spectrometry confirmed that mineral Ca intensified N-related reactions, including dehydration, decarboxylation, dehydrogenation, and deamination of protein-N. This study could guide pyrolytic production and subsequent application of biochar/biofuel, as well as exhaust gas collection regarding N recovery and pollution control.

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