Automated image analysis and hyperspectral imagery with enhanced dark field microscopy applied to biochars produced at different temperatures

Biochar from agricultural biomasses and solid wastes represents a win-win solution for a rational waste management. Its sustainable usage requires the identification and standardization of biochar characteristics. The aim of this work was to identify the physical-chemical and spatial characteristics of biochars from pruning residues (PR), poultry litter (PL), and anaerobic cattle digestate (CD) at two pyrolysis temperatures (350\ub0C and 550\ub0C). The biochar characterization was carried out by applying emerging imaging techniques, 2D automated optical image analysis and hyperspectral enhanced dark-field microscopy (EDFM), and by SEM analysis. As predictable, the feedstock composition and the pyrolysis temperature strongly influence the physical structures of the biochar samples. Irrespective of charring temperature, PR biochar was mainly characterized by a broken and fragmented structure with an irregular and rough particle surface, completely different from the original PR wood cell. The EDFM imaging analysis evidenced the thermal degradation of PR vegetal products, composed primarily of hemicellulose, cellulose and lignin. On the contrary, small and regular particles with a smooth surface were produced by the PL pyrolysis, especially at 550\ub0C, due to the lower PL morphological homogeneity in comparison with the other biomasses. Finally, CD charring at both temperatures was characterized by changes in chemical composition, suggested by a lower pixel intensity. In conclusion, the emerging imaging techniques used in this study proved to be very effective in analyzing some properties of biochars, and can, therefore be considered as promising experimental strategies for detecting the feedstock and pyrolysis temperature of biochar

Characterization of chemical\u2013physical, structural and morphological properties of biochars from biowastes produced at different temperatures

Biochar production from biowastes (e.g. digestate) is currently one of the more innovative and unexplored fields of research. A complete characterization of these materials, also according to the production temperature, would be a key tool to assess their potential use as soil amendments. For this purpose, five feedstocks (sewage sludge, municipal organic waste, cattle manure and silage digestates, poultry litter and vineyard pruning residues) were pyrolyzed at different temperatures. Structural and morphological transformations of biomasses during heating were followed by using FT-IR, scanning electron microscopy (SEM) and hyperspectral enhanced dark-field microscopy, a novel technique that provides both spectral and spatial information in one measurement. In addition, biochar microstructure (i.e. surface area and pore size distribution) using CO2 and N-2 adsorption isotherms was investigated. Specific density was also analysed by a helium pycnometer. Biochars exhibited considerable chemical, structural and morphological differences depending on temperature and feedstock type. Moreover, specific density and surface area increased with the temperature. In particular, heating was able to produce a sharp increase of mesopore and micropore volume especially at 450 and 550 A degrees C, but with different intensities for each feedstock. Thanks to the hyperspectral analysis, distinctive spectral patterns depending on the biochar chemical composition as well as the spatial distribution of the components were found. The results demonstrated that, from a physical-chemical point of view, it is not possible to identify an "ideal" biochar able to improve both soil nutrient content and structure. On the contrary, depending on feedstocks and temperature, each biochar exhibits specific features that would make it suitable for a specific purpose