Mineral Concentration in Selected Native Temperate Grasses with Potential Use as Biofuel Feedstock

Authors: El Nashaar, Hossien; Griffith, Stephen; Steiner, Jeffrey; Banowetz, Gary

Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/9/2009
Publication Date: 6/30/2009
Citation: El Nashaar, H.M., Griffith, S.M., Steiner, J.J., Banowetz, G.M. 2009. Mineral Concentration in Selected Native Temperate Grasses with Potential Use as Biofuel Feedstock. Bioresource Technology. 100:3526-3531.

Interpretive Summary: There is considerable interest in converting agricultural residues into energy products, especially to reduce the need for imported oil. One agricultural residue that is plentiful in the Pacific Northwest is straw from grass seed-producing and cereal grain cropping systems. Economical conversion of straw to energy has been plagued by high costs to transport this low density feedstock. One alternative to transporting the straw is on-farm or local conversion to energy. This would require local-scale technologies capable of performing the conversion. One potential technology is a thermochemical approach, gasification. Previous attempts to develop gasification units to convert straw to energy were plagued by anti-quality mineral constituents that reduced the long-term durability of gasifiers. We analyzed the mineral content of straws from a selection of grasses collected from multiple locations to determine whether some grasses would be more suitable feedstock for gasification conversion. We also quantified the content of minerals in the straw that represent potential soil nutrients that would be removed from crop fields by straw harvest. We discovered that significant variability in mineral composition existed, particularly in critical anti-quality. The accumulation of silicon (Si), potassium (K), sulfur (S) and chloride (Cl) varied between species and locations. Analyses of soils from eight locations suggested that variability in plant mineral composition may be due to soil nutrient content, but differences between species collected at the same location suggest fundamental differences in how these grasses take up minerals from the soil. Soil and plant mineral composition needs to be considered when determining the quality of bio-feedstocks or attempting to genetically improve grasses to enhance their potential use as biofuel feedstock.

Technical Abstract: National and state bio-based energy initiatives have focused interest in conversion of agricultural residues into energy products. One plentiful residue in the Pacific Northwest is straw from grass seed-producing and cereal grain cropping systems. Previous efforts to utilize thermochemical approaches to convert straw to energy were plagued by high transportation costs of this low density feedstock material and by anti-quality mineral constituents that impact the long-term durability of thermochemical technologies. We conducted mineral analyses on straw from a selection of grasses collected from multiple locations to determine if there were genotypic differences in the accumulation of minerals that negatively impact thermochemical gasification conversion. We also quantified the content of minerals that represent potential soil nutrients that would be removed from crop fields by straw harvest. Significant (P < 0.01) variability in mineral composition was measured, particularly in critical anti-quality minerals that impact the suitability of straw for thermochemical conversion to synthesis gas by gasification. The accumulation of silicon (Si), potassium (K), sulfur (S) and chloride (Cl) varied between species and locations. Analyses of soils from eight locations suggested that variability in plant mineral composition may be due to soil nutrient content, although more analyses are required to quantify the relationship between soil mineral content and plant accumulation. The differences between species collected at the same location suggest the existence of genotypic differences. There were also differences among locations for the same species. Soil and plant mineral composition needs to be considered when determining the quality of bio-feedstocks or attempting to genetically improve grasses to enhance their potential use as biofuel feedstock.