Effect of Heating Time and Temperature on the Chemical Characteristics of Biochar from Poultry Manure

Poultry manure (PM) chars were obtained at different temperatures and charring times. Chemical–physical characterization of the different PM chars was conducted by cross-polarization magic angle spinning (CPMAS) 13C NMR spectroscopy and thermal analysis. CPMAS 13C NMR spectra showed that the chemical composition of PM char is dependent on production temperature rather than on production duration. Aromatic and alkyl domains in the PM chars obtained at the lowest temperatures remained unchanged at all heating times applied for their production. The PM char obtained at the highest temperature consisted only of aromatic structures having chemical nature that also appeared invariant with heating time. Thermogravimetry revealed differences in the thermo-oxidative stability of the aromatic domains in the different PM chars. The PM char produced at the highest temperature appeared less stable than those produced at the lowest temperatures. This difference was explained by a protective effect of the alkyl groups, which are still present in chars formed at lower temperature. The analysis of the chemical and physicochemical character of poultry manure chars produced at different temperatures can increase understanding of the role of these materials in the properties and behavior of char-amended soils.