The advent of industrial, fertilizer-intensive agriculture during the 20th century has promoted export of anthropogenic nutrients, spurring degradation of ecosystem biodiversity and water quality. Exported nitrogen and phosphorus are recognized drivers of this deterioration, and require management. In the mid-1990s, denitrifying bioreactors (DNBRs), a subsurface, edge-of-field best management practice (BMP) that intercepts and treats agricultural drainage by supporting nitrate-attenuating denitrification with a saturated, carbon-filled substrate, were developed. Since then, their utility has expanded, and recent studies have unearthed biochar's capability to stimulate simultaneous nitrate (NO3--N) and phosphate (PO43--P) removal in DNBRs. This study investigated biochar's potential as an amendment to the traditional woodchip media by conducting nine, five-day trials on twelve laboratory-scale, horizontal flow-through DNBR columns. Three media types were tested: woodchips (W), 90% woodchips and 10% biochar (B10), and 70% woodchips and 30% biochar (B30). Simulated agricultural drainage with four unique concentration combinations of 16.1 and 4.5 mg L-1 NO3--N and 1.9 and 0.6 mg L-1 PO43--P was delivered at hydraulic retention times (HRTs) of 3, 6, and 12 h. Mean NO3--N removal efficiencies ranged from 16.9%-93.7%, and media type was insignificant at low influent NO3--N concentrations, but B30 was the most effective at high influent NO3--N concentrations. Mean PO43--P removal efficiencies ranged from -122.0%-74.9%, with B10 and B30 significantly worse than W at removing PO43--P. These findings corroborate previous work indicating boosted NO3--N removal with biochar, but contradict studies upholding PO43--P-removing capabilities. / Master of Science / Nitrogen and phosphorus-containing nutrients are applied to agricultural fields for supporting higher crop yields, and once these nutrients are exported they can negatively impact ecosystem biodiversity and water quality. These nutrients therefore require management. Denitrifying bioreactors (DNBRs) are subsurface engineered structures that intercept and treat agricultural drainage by supporting nitrate-removing denitrification with a carbon substrate. Recent studies have unearthed the potential of biochar, which is a type of charcoal typically used for soil amendment, as a substrate for promoting simultaneous removal of nitrogen and phosphorus.
This study investigated biochar’s potential as an amendment to the traditional DNBR woodchip media using laboratory-scale DNBRs that were subjected to different hydraulic retention times and influent nutrient concentrations.
Results revealed that the biochar did not significantly enhance nitrate removal under low influent nitrate concentrations, but did significantly improve nitrate removal at high influent nitrate concentrations. The biochar-amended treatments were significantly worse than the woodchip treatments at supporting phosphate removal.
These findings suggest that biochar may indeed boost nitrate removal, but may not improve phosphate removal.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/81880 |
| Date | 19 January 2018 |
| Creators | Coleman, Brady S. |
| Contributors | Biological Systems Engineering, Easton, Zachary M., Sample, David J., Stephenson, Stephen Kurt |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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