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In-situ aquifer denitrification using a daisy well system

Imtiyaz Ahmed Khan, University of Nebraska - Lincoln

Abstract

A daisy well system was designed to induce denitrification in a shallow sand and gravel aquifer that is contaminated with 40 mg NO3-N L −1. The system contains a 6-inch diameter centrally located production well surrounded by eight 4-inch diameter outer injection wells and eight 2-inch diameter inner injection wells. The outer and inner injection wells were located 40 and 20 ft from the production well, respectively. The wells were screened 38 to 48 ft below the ground surface. The production well was operated continuously at a rate of 40 GPM, and the rate of injection was 10 GPM. ^ Experiments were conducted using continuous and pulse injection of organic carbon (ethanol or acetate). In both cases, the nitrate concentration was reduced to below the detection limit (<0.1 mg NO3-N L−1) in the impacted zones. Under continuous injection, accumulation of bacterial exudates in the vicinity of the injection well resulted in injection well clogging within 10 days. Using a dipole tool, periodic cleaning of the injection well by circulating a cleaning solution (5% H2O2 and 0.1% NaOH) proved unsuccessful in sustaining the denitrification process. Experiments with pulse injection successfully alleviated the proliferation of bacterial exudates near the field of injection without adversely affecting the performance of the denitrification process. ^ In comparison to acetate, ethanol favors the enhanced growth of bacteria and associated slimy secretions which increase the risk of biofouling. During ethanol injections, residual DOC concentration in the DNZ should be monitored closely and injectate carbon concentrations adjusted to prevent undesirable sulfur reduction. ^ About 45% of the nitrate was reduced before it was intercepted by the production well during a three month pulse injection. In municipalities where nitrate contamination is <15 mg>NO3-N L−1, this reduction would be sufficient to bring nitrate levels to compliance. Periodic injections of hydrogen peroxide in the inner wells greatly improved the quality of the extracted denitrified water. However, it is recommended that the denitrified water should be filtered and disinfected before discharging in the potable mains. ^

Subject Area

Agriculture, Agronomy|Agriculture, Soil Science|Engineering, Environmental

Recommended Citation

Khan, Imtiyaz Ahmed, "In-situ aquifer denitrification using a daisy well system" (2000). ETD collection for University of Nebraska - Lincoln. AAI9967380.
http://digitalcommons.unl.edu/dissertations/AAI9967380

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