NITRATE AND PHOSPHORUS REMOVAL IN BIOCHAR-AMENDED DENITRIFYING BIOREACTOR

Denitrifying bioreactors are an effective means to combat eutrophication, as microbes within the chamber, supported by the inner carbon source, stimulate denitrification. Woodchips have been regarded as the most effective carbon source, primarily due to their cheap cost, low decay rate, and ability to remove significant nitrate. However, this substrate facilitates substantial greenhouse gas emission. Recent work has called for the assessment of biochar as a substrate additive to support complete denitrification, minimize greenhouse gas emission, and provide the additional benefit of phosphate reduction. However, these studies were conducted in a laboratory setting and did not test biochar in a field-scale bioreactor. This study compared two ~8.6 m³ bioreactors, one of which contains 100% woodchips and the other of which contains 90% woodchips and 10% biochar. Water from a nearby irrigation pond was pumped into both denitrifying bioreactors during 11 artificial events. Concurrent gradual dissolved Ca(NO₃)₂ addition was performed in an attempt to mirror a natural event in which the bioreactors were flooded with a substantial volume of uniformly mixed, nitrate-rich agricultural effluent. Samples were taken from bioreactor wells every 0.5 to 3 hours after each event, and sampling frequency decreased as time elapsed. After field filtering the samples through 0.45 µm nylon filters, HDPE bottles were used for storage. Any unfiltered bottles remained submerged in ice until filtering was possible. Once filtered, all samples were stored in a freezer at -4ºC until _­NO₃^--N, PO₄^3--P, and NH₄⁺-N concentrations were determined via flow injection analysis (Lachat QuikChem 8500 series 2). We expect enhanced nitrate and phosphate reduction within the biochar-amended bioreactor in comparison to the woodchips bioreactor.