The 600 acres of crop and forest land in close proximity to the Penn State University campus is interlaced with irrigation pipes carrying and discharging over 500 million gallons per year of primarily treated wastewater. This “living filter” system was developed and constructed in the 1960s and provides a unique opportunity for university scientists to study the long-term effects of irrigation with wastewater; is biomagnification of pollutants occurring within this system? Or are plants uptaking nutrients and soil microbes filtering compounds before they can reach groundwater?
The Tres Rios constructed wetland system provides tertiary treatment to wastewater from a plant in southwestern Phoenix, AZ prior to discharge into the Salt River.
Emily Woodward is leading a current project investigating solute modeling and transport of compounds in the living filter system with a team of collaborating researchers. Their results were recently published in the Journal of Environmental Quality in the November-December 2014 volume. Woodward’s team sampled soils from the layer that separates the water table from the soil surface, termed the vadose zone. They evaluated these samples for accumulation of chemical compounds known to be in wastewater, if their presence was confirmed, it could be assumed the vadose layer was protecting groundwater from impact.
This research team is specifically concerned with those compounds defined as Endocrine Disrupting Compounds, or EDCs. There are 3 main compounds of interest in this study: 17β-estradiol and estrone are naturally produced in animals, and 17α-ethynylestradiol which is a synthetic hormone found in birth control medications which is thought to enter the water system by being flushed down toilets or in the sink drain. In the U.S. water flushed down toilets and drains is carried to wastewater treatment plants and then usually it is discharged into streams and rivers. While treatment in plants takes care of nutrients and pollutants, EDCs may not be eliminated through this process. Outcomes in the environment have not been directly determined, but EDCs have been shown to severely affect aquatic life and are thought to affect the function of human hormonal systems.
The soil samples collected and analyzed by the Penn State research team contained estrone and 17β-estradiol in higher concentrations than those found in sites not irrigated with wastewater. However, concentrations of 17α-ethynylestradiol, the synthetic hormone, were very similar between the two types of sites. The land use type seemed to greatly affect concentration levels; forested sites had higher EDC accumulation that land being used for agriculture. This difference may be attributed to amounts of organic carbon present in the soil, carbon bonds compounds and slow their transport through the soil. Soils in the forested area had approximately 3 times the amount of carbon as soils in croplands.
The next step in Woodward’s research process is evaluating levels of EDCs present in wells near the living filter site. These results could definitively indicate soil’s ability to filter out EDCs and prevent groundwater contamination. This research has exciting indications for the advantages of wastewater reuse which can help conserve water, improve groundwater quality and increase habitat value.
