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Improving denitrification bioreactor efficacy on the microbial, property, and regional scales
AdvisorSchmidt, Casey A.
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The Santa Fe River watershed in North Central Florida has a significant nitrogencontamination problem that is causing eutrophication in both the river and the manysprings in the area. The watershed is dominated by agriculture, which has been identifiedas the main source of the eutrophication. One solution is to build a denitrificationbioreactor or denitrification wall that removes nitrogen in situ. The objective of this studywas to install a 320-meter denitrification wall to remove property-scale nitrogen loadscoming off of a commercial nursery. This study analyzed efficacy of this reactor on threedifferent scales: on the microbial level to understand of community composition and todevelop optimization strategies; on the well transect level to understand the reactor’simpact on water quality, and regionally using GIS to identify suitable locations wherethese walls could be placed. Based on water quality analysis from 6 well transects,nitrate-nitrogen levels decreased, on average, from 7.1±3.2 mg/L to 1.3±0.6 mg/L, whichis a nitrate load reduction of 3,000 kg-N/yr. The reactor is also cost effective with a totalinstallation cost of $50,000, which is $1.73/kg-N over an estimated 20 year lifespan. Thiswall had lower overall removal efficiency rates around 70-75% compared to previousreactors that had removal efficiencies of 90% and above, which was likely due to lowerhydraulic conductivity in this wall. The installation of the wall caused a 6% increase inmicrobial diversity and was largely dominated by anaerobic genera, including knowndenitrifiers. Additionally much of the variability was explained by environmental factorslike total organic carbon, nitrate concentrations, and conductivity. The spatial assessmenttool identified close to 40 square kilometers across the Santa Fe River watershed assuitable locations.