Denitrifying Bioreactor In Situ Woodchip Bulk Density

Abstract

Highlights The bulk density of woodchips in denitrifying bioreactors in the field is unknown. In situ bulk density estimation methods were developed for use during construction or excavation. Dry bulk densities of aged woodchips at bioreactor bottoms were lower than previous literature values. Moisture and particle size and density explained some, but not all, of the variation in in situ bulk densities. Abstract. Woodchip bulk density in a denitrifying bioreactor governs system hydraulics, but this prime physical attribute has never been estimated in situ. The objectives were twofold: (1) to establish estimates of in situ woodchip bulk density at bioreactors in the field, and (2) evaluate causal factors for and resulting impacts of these estimates. Proof-of-concept bulk density methods were developed at a pilot-scale bioreactor using three ways to estimate volume: surveying the excavated area, pumping the excavation full through a flow meter, and using iPhone Light Detection and Ranging (LiDAR). These methods were then further tested at two new and three old full-size bioreactors. Additional ex situ (off-site) testing with the associated woodchips included analysis of bulk density along a moisture gradient and particle size, particle density, wood composition, and hydraulic property testing. In situ dry bulk densities based on the entire volume of the new bioreactors (206-224 kg/m3) were similar to values from previous lab-scale studies. In situ estimates for woodchips at the bottom of aged bioreactors (22-mo. to 6-y) were unexpectedly low (120-166 kg/m3), given that these woodchips would presumably be the most compacted. These low moisture-content corrected dry bulk densities were influenced by high moisture contents in situ (>70% wet basis). The impacts of particle size and particle density on bulk density were somewhat mixed across the dataset, but in general, smaller woodchips had higher dry bulk densities than larger, and several woodchips sourced from the bottom of bioreactors had low particle densities. Although dry bulk densities in the zone of flow in bioreactors in the field were shown to be relatively low, the resulting permeability coefficients under those packing conditions did not differ from those of the original woodchips. The LiDAR-based volume estimation method was the most practical for large-scale, full-size evaluations and allowed high precision with small features (e.g., vertical reactor edges, drainage fittings). Keywords: Compaction, Cone penetrometer, Drainable porosity, LiDAR, Moisture content, Survey.

Greening America's Rivers: The Potential of Climate Financing for Nature-Based Water Quality Improvement

“…Mean nutrient removal percentages and treatment costs came from the 2016 Illinois Nutrient Loss Reduction Strategy report [34]. All values used within this analysis fall within the range of values reported in the literature [33,35,36,37,38,39,40,41,42,43,44,45,46].…”

“…The descriptions in the following sections are meant to be used in unison with the supplemental spreadsheet with LCA calculations. For all LCA estimates, calculations were performed for a 50 acre square farm with mean annual nutrient loss of 9.5 kg N/acre and 0.65 kg P/acre [37,63]. Costs and emissions for green nutrient treatment technologies were assumed to scale linearly based on the number of acres treated, so the 50 acre farm was used to calculate per acre treatment emissions of all treated farmland.…”

“…Assumptions used for the LCA of a woodchip bioreactor were gathered from Christianson et al [37]. It was assumed that a 10 yard long, 5 yard wide, and 3 yard deep bioreactor would be required to treat 50 acres of farmland.…”