THE LIVING FILTER: MONITORING NITRATE ACCUMULATION AFTER 50 YEARS OF WASTEWATER IRRIGATION

Open Access
Author:
Hagedorn, Jacob Gerrit
Graduate Program:
Geosciences
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
December 04, 2015
Committee Members:
  • Demian Saffer, Thesis Advisor
  • Michael Allan Arthur, Committee Member
  • Susan Louise Brantley, Committee Member
Keywords:
  • Living Filter
  • Nitrogen
Abstract:
As global freshwater sources decline due to environmental contamination and a growing population, there is an increasing need for sustainable wastewater renovation techniques to ensure fresh water for future generations. Wastewater re-use is one way to simultaneously reduce freshwater use and recycle valuable nutrients into ecosystems. The Living Filter, located on the campus of The Pennsylvania State University, is an example of a wastewater renovation system. For fifty years, Penn State has sprayed treated wastewater onto agricultural fields and forest ecosystems, leaving natural processes to further filter the wastewater. The localized water recycling process is considered sustainable because the wastewater filters through the soil, providing nutrients to agricultural crops and forests, until it eventually reaches the groundwater system where it is extracted for university drinking water again. Previous studies at the Living Filter have examined soil physical property changes, surface runoff water quality, and phosphorous accumulation. However, most of these studies have only examined these issues in the first 120 cm of the soil profile. Few investigations into deeper subsurface profile phenomena have been conducted. Given that spray irrigation has occurred for 50 years, the concern for excess nitrogen in the subsurface, and that deeper soil profile studies have not been conducted, the purpose of this project was to analyze the potential for nitrate saturation and more broadly the fate and budget of nitrogen in the system. This study examines the cycling and accumulation of nitrate, and investigates the factors that control nitrate accumulation. Using a combination of soil core and monitoring tools, ecosystem indicators including soil nutrient capacities, moisture levels, and soil characteristics were measured. Comparing data from the time of initial system installation to present illuminates how the system has changed. Results reveal a systematic difference between irrigated and non-irrigated soil nitrate concentrations, regardless of land use. Spray field soil nitrate concentrations were elevated compared to non-irrigated sites; however, it is difficult to determine if that is caused by just spray irrigation or by fertilizer input. Although elevated, groundwater concentrations are below the EPA drinking water threshold. Soil analysis including particle size distribution, soil elemental composition, and texture did not distinctively illuminate factors that control nitrate accumulation, whereas it is generally understood that porosity, soil moisture, and soil texture all impact nitrate presence. The results of soil analysis did match previous studies in that only weak relationships were found between specific soil characteristics and soil nitrate accumulation in the field area. The nitrogen budget analysis revealed that the soil incorporation in the Living Filter serves as an important N sink, but there is unaccounted nitrogen that could be incorporated by soil processes besides adsorption accumulation. These findings suggest that spray irrigation at the Living Filter under the current rates of application has not caused the ultimate stage of nitrogen saturation to occur in the spray irrigation site, although there is evidence of nitrate bypass at the site because groundwater concentrations beneath the Living Filter are continually above background levels. Because groundwater nitrate concentrations are below regulated thresholds, and soil nitrate concentrations are less than sprayed nitrate concentration inputs, the system can be interpreted to not have reached capacity nitrogen saturation, and the ecosystem continues to use nitrogen and transform it. Analysis of effects of variation in land use illuminates possible causes of differences in soil nitrate concentrations. From the viewpoint of nitrate accumulation and potential for environmental contamination, the Living Filter continues to serve as a viable mechanism for absorbing nutrient discharge and serving as the final stage of wastewater treatment after fifty years, although should be continually monitored.