Range of and relationships between physical and hydraulic properties of commonly available denitrifying bioreactor woodchips
Saturated hydraulic conductivity (Ksat), porosity, and particle size are key physical parameters of woodchip media for denitrifying bioreactor design. Current design guidelines can be improved by analyzing more woodchip types and the effects of overburden on woodchip properties. The objectives of this study were to quantify and determine the relationships between Ksat, porosity, particle size, and bulk density of 21 woodchip types from the United States Midwest region to improve bioreactor design specifications. Saturated hydraulic conductivity was estimated using constant head permeameters and Darcy’s Law assumptions. Drainable porosity was assessed both by packing 1 L beakers (“jar method”) and in the permeameters. Particle size analysis was performed using a sieve shaker, as well as by manually measuring the longest, middle, and shortest axis of individual woodchip particles with a caliper. High compaction methods limited the range and magnitude of Ksat for 20 typical woodchip types to 0.10 to 2.05 cm s-1. Reduced compaction increased Ksat and drainable porosity for a subset of woodchips to values closer to current practice standards (2.07 to 7.44 cm s-1 and 41 to 55%, respectively). Drainable porosity (permeameter method) and hand-measured woodchip median width were the only significant predictors of Ksat in a multiple linear regression model (Ksat = 0.081*DPperm + 0.048*Wmed; R2 = 0.48), however the model was limited by the small range in Ksat values resulting from high compaction. These results can inform bioreactor design specifications but better guidance can be provided by contextualizing these results with in situ bulk density measurements which are suggested as future research.
denitrifying bioreactor design, saturated hydraulic conductivity, porosity
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign