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News Article

Emerging contaminants

Soil filters out chemicals before reaching groundwater

Emerging contaminants are defined as chemicals that are not currently regulated but are important because the risk they pose to both human health and the environment is not yet fully understood.  While there remains some uncertainty regarding the impact of these contaminants on groundwater resources and aquatic ecosystems, a recent study by researchers at Pennsylvania State University has shed some light on the transport of these chemicals.

The research took place at the University’s wastewater treatment plant and Living Filter.  It involved analysing the fate of seven emerging contaminants, including acetaminophen, ampicillin, naproxen, ofloxacin, sulfamethoxazole and trimethoprim.   The aim of the study was to track the compounds all the way through the wastewater treatment plant, to the wells at the Living Filter to assess the contaminant removal efficiency of the plant and the ability of the Living Filter’s soil profile to provide further treatment of the compounds that were present in the effluent.

Once a week, from October 2016 to March 2017, after each treatment process was completed, 24-hour composite samples were collected.  Water samples were collected every month from 14 groundwater wells at the Living Filter. While not conclusive, the research findings were found to be useful and thought provoking, according to Heather Gall, assistant professor of agricultural and biological engineering.

"The study was unique in that it provided a snapshot of soil acting as a biogeochemical filter to remove some emerging contaminants," said Gall, who presented the research findings at the annual meeting of the American Society of Agricultural and Biological Engineers.

"Penn State was the ideal place to look at the movement of pharmaceuticals from wastewater to groundwater because the University has spray-irrigated all of its treated wastewater onto nearly 600 acres of agricultural and forested land known as the Living Filter since the early 1980s," said Gall. "And nearby wells allow us to look at concentrations of the chemicals that reached the relatively deep groundwater across the site."

Gall explains that overall, the study revealed that the wastewater treatment plant had effectively removed the acetaminophen and caffeine contaminants while showing some seasonal variability in the removal efficiency of the other compounds.  The activated sludge element of the treatment plant was the most effective phase for reducing the concentration of the contaminants.  They found that concentrations were at least one order of magnitude lower in the groundwater than in the effluent from the treatment plant, which suggested that the soil was acting as an effective biogeochemical filter, except during snowmelt events.

The study took place in a variety of different weather conditions, which affected how the plant dealt with the compounds.  For example, during winter conditions, microbes which break down and remove the contaminants were not as efficient.  However, these same conditions did not affect the ability of the soil to filter out the chemicals, although heavy precipitation and snowmelt events reduced the rate of removal, which meant that higher concentrations were found in the wells following these events.

"What was interesting about this project was that these samples primarily were taken in the cold months, and we don't often see field studies done during the winter. But that happened because the research project was part of the student's honours thesis, and done during the spring semester," said Gall. "So we saw the influence of cold conditions, freeze-thaw cycles, and heavy, prolonged rains."

These chemicals are considered to be water pollutants, but are as yet unregulated by any standards.  Advances in technology and analytical chemistry in recent years has improved the detection of these contaminants at very low concentrations in surface water, groundwater, wastewater and even drinking water; however their effects on non-target species are mostly unknown.

Article details

  • Author(s)
  • Stephanie Cole
  • Date
  • 02 August 2017
  • Source
  • Pennsylvania State University
  • Subject(s)
  • Pollution