Scientists Study Wastewater's Impact on Water Quality

A recent study from Penn State highlights critical issues in wastewater management in the Florida Keys, particularly how nutrients can foster harmful algal blooms and pollution in coastal waters. Researchers tracked the migration of these nutrients from disposal sites, revealing significant findings that have already influenced local wastewater practices.

Published in the journal ACS ES&T Water, the study summarizes two years of data collected from wastewater and groundwater monitoring. Many treatment facilities in the region perform biological and chemical treatments before injecting wastewater into shallow wells, typically less than 100 feet deep. The intention is for remaining nutrients, such as inorganic phosphate, to adhere to the porous limestone bedrock as the wastewater moves underground.

However, researchers detected signs of potential wastewater contamination in groundwater and nearshore areas, suggesting that current treatment and disposal methods may be inadequate. This prompted an environmental lawsuit against the city of Marathon, Florida, in 2022, resulting in a commitment to discontinue the use of shallow wells.

In 2021, scientists installed monitoring wells around Marathon's wastewater treatment facility and collected data on nutrients and synthetic compounds, including sucralose. While the shallow injection process effectively removed over 90% of soluble reactive phosphorus (SRP), both SRP and sucralose were still present in nearshore waters, indicating incomplete removal.

Miquela Ingalls, assistant professor of geosciences, stressed the need to reassess the use of shallow injection for treated wastewater. She pointed out that understanding whether wastewater injection is equivalent to direct contaminant discharge is complex, particularly in light of the Clean Water Act, which prohibits direct discharge into freshwater.

The study also revealed that the unique geology of the Florida Keys complicates matters. The porous carbonate bedrock is expected to bind phosphate, but the high salinity of the groundwater causes less dense wastewater to rise quickly, leading to rapid surface contamination.

The research team continues to analyze data from shallow injection wells, now focusing on levels of nitrogen, another critical pollutant. Ingalls explained that while phosphorus binds to bedrock, nitrogen's behavior is influenced by microbial communities in the subsurface. Both nutrients can contribute to eutrophication, resulting in increased algae growth and low-oxygen conditions detrimental to fragile marine ecosystems.