ARS | Publication request: Mineral nutrient recovery from pyrolysis systems

Submitted to: Journal of Environmental Progress and Sustainable Energy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 12, 2012
Publication Date: March 27, 2012
Citation: Wise, J., Vietor, D., Provin, T., Capareda, S., Munster, C., Boateng, A.A. 2012. Mineral nutrient recovery from pyrolysis systems. Journal of Environmental Progress and Sustainable Energy. 31(2):251-255.

Interpretive Summary: Bioenergy crops such as high-energy sorghum, bioenergy rice, corn stover, and switchgrass can be converted by pyrolysis, heating in absence of oxygen, to produce bio-oil, non-condensable gases, and biochar. The biochar fraction can be recycled back to the production field to improve soil physical qualities and nutrient status. We quantified the recovery of nutrients such as phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) in the pyrolysis products from various biomass feedstocks using two distinct reactors typically used to carry out pyrolysis at slow heat rate (fixed-bed reactor) and fast heat rate (fluidized-bed reactor). The results showed that P recoveries can be as much as 93% in a fixed-bed reactor and 58% in a fluidized-bed reactor for pyrolyzed high energy sorghum. Recoveries for K, Ca, and Mg varied along with the other feedstocks and reactor type, suggesting nutrient recovery is linked both to feedstock characteristics and reactor type. The results will assist farmers wishing to apply biochar for soil amendment and nutrient transport.

Technical Abstract: Bioenergy crops such as high-energy sorghum (HES), bioenergy rice, corn stover, and switchgrass can be thermo-chemically converted by pyrolysis to produce bio-oil, synthesis gas from non-condensable gases, and biochar. The biochar fraction can be recycled back to the production field to improve soil physical qualities and nutrient status. While various publications have demonstrated the beneficial effect of pyrolysis biochar on soil physical properties, there has been limited data published on the recovery of mineral nutrients from pyrolysis co-products. This work quantified the recovery of nutrients (P, K, Ca, and Mg) in pyrolysis co-products from various feedstocks using two distinct reactors. Nutrient mass balances, on a biomass basis, were calculated for the two reactors efficiency in the recovery of the nutrients. The results revealed P recoveries of 93% (fixed-bed reactor) and 58% (fluidized-bed reactor) for pyrolyzed HES. Recoveries for K, Ca, and Mg varied along with the other feedstocks and reactor type, suggesting nutrient recovery is linked both to feedstock characteristics and reactor type.