Hydraulic Properties of Baled Switchgrass and Miscanthus

Abstract. This study characterized the hydraulic properties within baled switchgrass ( L., variety Alamo) and miscanthus (x), thereby enabling a better understanding of moisture changes in baled biomass during on-farm storage and/or high-solids bioconversion. Fully saturated bales were drained by gravity, and the moisture content was determined over 60 h. The average initial moisture content ranged between 55.9% and 71.9% (w.b.) for switchgrass and between 60.5% and 73.9% (w.b.) for miscanthus bales depending on the dry bale density. As the bale drained by gravity, rapid leaching of water was observed within the first 0.1 h, with a reduction in moisture content of 7.3 and 7.0 percentage points (w.b.) for switchgrass and miscanthus, respectively. Leaching then continued at a steady rate until termination of the experiment, with further reductions of 4.3 and 4.4 percentage points (w.b.) for switchgrass and miscanthus, respectively. Final moisture contents after 60 h ranged from 45.8% to 58.3% for switchgrass and from 48.7% to 60% for miscanthus, with the higher moisture contents observed in the lowest density bales. Hydraulic conductivity tests were carried out with bales of switchgrass and miscanthus with a constant head system. The average saturated hydraulic conductivity ranged between 0.103 and 0.616 cm s-1 for baled switchgrass and between 0.219 and 0.658 cm s-1 for baled miscanthus depending on the bale density. The matric suction of baled switchgrass was also assessed at variable densities and moisture contents using the contact filter paper method. The van Genuchten parameters were found to range between 0.235 and 0.270 m-1 for α and between 5.415 and 10.345 for n, depending on the density. Infiltration tests were also carried out on baled switchgrass at variable densities and moisture contents using a minidisk infiltrometer. The curve-fitting parameters of Philip‘s two-term equation ranged between 0.086 x 10-6 and 0.779 x 10-6 cm s-1 for C1 and between 0.200 and 5.805 x 10-6 cm s-1/2 for C2, depending on the density and moisture content. The unsaturated hydraulic conductivity ranged between 0.019 and 0.272 cm s-1, while sorptivity ranged between 0.048 and 2.103 cm s-1/2, depending on the density and moisture content. These results provide data required to evaluate water flow through variable-density rectangular bales and indicate a potential to remove end-products of biomass conversion from baled biomass.

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