Center for Sustainable Environmental Technologies

The goal of this project is three fold: to characterize chars produced by CSET’s thermochemical processes, to test the char’s suitability as a bio-char soil amendment, and ultimately, to engineer and produce bio-chars that exhibit desirable agronomic properties.

Bio-char, by definition, is simply the solid product of a thermochemical process used for agronomic or horticulture purposes.  As soil amendments, chars from the thermochemical processing of biomass are believed to increase soil fertility by improving nutrient and water retention, lowing soil acidity and density, and increasing microbial activity.  In addition, energy produced from the thermochemical processing of biomass that stores carbon as bio-char in the soil can be considered carbon negative due to bio-char’s high recalcitrance.

Multiple physical, chemical and soil analyses are used to characterize these chars to better understand how production conditions relate to end product bio-char properties.  Among the analyses are particle size distribution by sieving, moisture and volatile content by thermogravimetric analysis (TGA), ash analysis by combustion, mercury intrusion and gas sorption porosimetry for BET surface area and pore size distribution, and particle density by pycnometry.  Elemental CHNOS analysis and X-ray fluorescence spectroscopy (XRF) quantifies the char’s chemical and trace mineral content. (The majority of mineral nutrients from biomass are retained in the char; using char as a soil amendment returns these nutrients to the soil.)  Fourier-transform infrared spectroscopy (FTIR) provides information about available surface functional groups and cation exchange capacity (CEC).  Finally, solid state nuclear magnetic resonance (NMR) is used to estimate the char’s degree of aromaticity, which is believed to relate to its long term stability in soil.     

Chars from fast pyrolysis and gasification of switchgrass and corn stover are being studied first as a baseline for locally-producible bio-chars.  After characterization, various lab, pot and field trials, conducted in collaboration with agronomists at ISU, will determine which kinds of bio-chars are the most successful as soil amendments.  From there, new bio-chars can be engineered from a wide range of biomass feedstocks using optimized thermochemical processing conditions for additional pot and field trials.