Submitted to: Journal of Analytical & Applied Pyrolysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 6, 2013
Publication Date: September 19, 2013
Citation: Uchimiya, M., Ohno, T., He, Z. 2013. Pyrolysis temperature-dependent release of dissolved organic carbon from plant, manure, and biorefinery wastes. Journal of Analytical & Applied Pyrolysis. 104:84-94. Interpretive Summary: Biochar is a solid co-product formed during the controlled heat treatment of agricultural wastes to produce bioenergy. Very small portion of biochar is expected to be water-soluble. This water-soluble fraction can become available to the plant/microbial community in the amended soils. Little information is available to understand how heat treatment conditions will influence the chemical structure of this water-soluble biochar fraction. In this study, water-extracts of biochars were analyzed by a highly sensitive fluorescence technique. Statistical analysis of fluorescence results showed more condensed chemical structure of water-soluble fractions, when the biochar was produced at higher temperature. Demonstrated fluorescence technique will also be useful for understanding the time-dependent changes in soluble organic carbon composition of biochar amended soils.
Technical Abstract: Limited information is available to understand the chemical structure of biochar’s labile dissolved organic carbon (DOC) fraction that will change amended soil’s DOC composition. This study utilized the high sensitivity of fluorescence excitation-emission (EEM) spectrophotometry to understand the structural changes in biochar-derived DOC as a function of feedstock and pyrolysis temperature (350-800 °C). Regardless of feedstock (almond shell, broiler litter, lignin, cottonseed hull, and pecan shell), low temperature (350-400 °C) pyrolysis shifted EEM of hot water (80 °C for 16 h) extracts towards longer emission wavelengths, indicating increased aromaticity. Five component parallel factor (PARAFAC) modeling of EEM afforded fulvic-like (C1), UVC humic-like and UVA marine humic-like (C2), UVC and UVA humic-like (C3), microbial decomposition products (C4), and protein-like (C5) components. Relative contribution of fulvic-like component (C1) exceeded that of humic-like fractions, and increased as a function of pyrolysis temperature. C4 showed disproportionately high contributions to 500 °C broiler litter and cottonseed hull biochars. First derivative ATR-FTIR analyses of biochars indicated that C4 represented carboxyl and other transient thermal degradation intermediates. C5 was attributable to thermally stable DOC fraction of lignin-rich biomass (pecan shell and lignin). Overall, fluorescence EEM and PARAFAC techniques provided rapid, quantitative structural information on biochar’s DOC that could not be obtained from bulk (proximate, ultimate, FTIR) analyses.