Constructed Wetlands as Remediation Tools for Shallow Groundwater Contaminated by Swine Lagoon Seepage

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Title: Constructed Wetlands as Remediation Tools for Shallow Groundwater Contaminated by Swine Lagoon Seepage
Author: Hathaway, Jon Michael
Advisors: Robert O. Evans, Committee Chair
Michael R. Burchell II, Committee Member
Stephen W. Broome, Committee Member
Abstract: Swine waste is typically flushed from beneath confinement houses into anaerobic lagoons for temporary storage and partial treatment. When improperly constructed, studies have shown that there is potential for the high strength wastewater to leak from the lagoon into the surrounding groundwater. Constructed wetlands have been implemented as treatment systems for wastewater. Biogeochemical reactions in wetlands make them viable options for wastewater treatment. Wetlands may remove pollutants such as nutrients through adsorption, nitrification, denitrification, and plant uptake. Studies have shown that constructed wetlands are able to attenuate substantial amounts of nitrogen and phosphorous from wastewater. Denitrification is the primary mechanism by which nitrogen is removed from wastewater in constructed wetlands. Research has shown that nitrification of ammonium nitrogen to nitrate may indirectly limit denitrification. One practice that may increase the nitrogen assimilation in a constructed wetland is the use of a nitrification pretreatment system such as a trickling filter. A trickling filter contains media on which nitrifying bacteria can attach, and provides an aerobic environment in which the nitrification process can take place. This study evaluated a site where a swine lagoon had leaked into the surrounding groundwater. The swine lagoon was eventually closed-out and a plan to pump out the contaminated groundwater was initiated. The goal was to pump at a rate that would change the subsurface gradient causing the contaminated water to stop flowing towards a nearby stream. The water was pumped into a constructed wetland where nutrients could be removed. After three years of pumping the contaminated groundwater, a trickling filter was implemented to nitrify the wastewater before it was discharged into the wetland. Over the course of the study, the average NH4-N concentration in wells located down gradient of the former lagoon decreased by more than 60%, and the hydraulic gradient between the former lagoon and the nearby stream was reduced by greater than 65%. The constructed wetland assimilated greater than 76% of the total nitrogen and more than 22% of the total phosphorous that it received, resulting in the assimilation greater than 915 kg of total nitrogen and more than 145 kg of total phosphorous. The nitrification pretreatment system converted 20% of the NH4-N it received to NO3-N on a mass basis. In the samples taken from the trickling filter, the arithmetic average amount of NH4-N that was converted to NO3-N was 37%. Although the nitrification pretreatment system was functional, there was no identified increase in total nitrogen assimilation within the constructed wetland. This may have been due to influent ammonium nitrogen concentrations becoming too low for the trickling filter to function at maximum efficiency by the time it was incorporated into the system.
Date: 2005-02-04
Degree: MS
Discipline: Biological and Agricultural Engineering
URI: http://www.lib.ncsu.edu/resolver/1840.16/1350


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