Imperfect underground processes help filter wastewater in Florida Keys

For seaside communities reducing their pollution, nitrogen is a main target. Often found in agricultural runoff and human waste, nitrogen and nitrate molecule containing nitrogen can enter coastal waters as a critical nutrient for algae. Its abundance leads to an excess of algae proliferations, overwhelming delicate balances of vegetable and marine life.

Many communities in southern Florida have treated wastewater – which contains nitrate and more – by injecting it underly in the ground under the table of groundwater. Microbes living in groundwater in the rocky porous limestone substratum convert and consume nitrate derived from gas gas or ammonium. But underground microbes are an imperfect antidote – if not useful – for the nitrogen of wastewater in Florida Keys, an observation which, according to researchers from Penn State, could help other coastal areas with their cleaning strategies. Scientists have reported their potential results and applications in The filing fileA newspaper in sedimentology.

The Penn State team had previously evaluated phosphate – a nutrient involved in many biological processes and applied in industry products, such as fertilizer – and its withdrawal of shallow injected wastewater near a treatment establishment in marathon, Florida.

Also in the background for the study of nitrogen, the treatment plant releases effluents to 60 to 90 feet under the ground in the porous foundation of the rhythm substratum near the coast. Samples from a range of underground water wells positioned between the effluent injection well and the coasts of Florida bay and the port of Key, which both lead to the Atlantic Ocean, between 2021 and 2023, the researchers constantly found appreciable nitrogen and phosphorus had migrated to shore. This indicates that if the underground microbes have converted and consumed part of the nitrate and phosphate, they failed to capture all the nutrients.

“Nitrate and phosphate are considerably reduced between injection and the time when the effluent reaches sharing waters,” said the main author Miquela Ingalls, assistant professor of geosciences at the Penn State land and mineral sciences. “However, the levels of contaminants have largely moved over time. The quantity of nitrate and phosphate had already been removed from the water, or has remained, varied by orders of size.”

Variability is probably linked to seasonal differences in the volume of wastewater and phosphate interactions with the rocky porous carbonate substratum, said Ingalls, explaining additional research would be necessary to confirm.

Funded by the Environmental Protection Agency, phosphate and nitrogen studies focused a sampling of contaminants in the National Marine Sanctuary of Florida Keys. Officials are concerned about the dangers for ecosystems already in danger, the researchers said.

The team also wanted to establish whether the shallow injections serve as a functional equivalent of the direct untreated wastewater discharge. The term – “functional equivalent” – is at the heart of a decision of the United States Supreme Court in 2020, when the judges decided that permits are necessary for direct discharges – or their equivalent – in navigable waters. Shallow injections under the groundwater table also require permits under standard environmental regulations.

The researchers have found that injections are not equal to the direct discharges of the ocean, explaining that biogeochemical cycles occurring in the route that waste brought back to surface water considerably filter its content compared to a direct discharge.

However, Ingalls said that nitrogen results point out that effluents may need more journey time from the injection point to coastal waters to better filter contaminants and avoid the harmful effects of the ecosystem.

“The shallow injection is not 100%effective,” said Ingalls. “So you always inject a certain quantity of these contaminants in the ecosystem surrounding the keys.”

One solution may be to modify the chemical composition of the effluent for greater salinity and density, she said. This approach could prevent the buoy discharge so quickly on the surface, which gives it more filtration time, said Ingalls.

The municipal council of Marathon agreed in 2023 to move away from the shallow injection. An environmental group had continued the city during the practice, partially citing certain preliminary data of the study of anterior phosphate.

“After the decision of the Supreme Court, the state tried to move away from the practice of shallow injections,” she said. “But it’s a financial burden.”

Additional research will plunge the process called adsorption more, when phosphate binds to the foundation of carbonate, made of ancient coral reefs. In a follow -up project, the researchers explore how long phosphate remains attached and the ease with which it can dissolve in the water.

Lee Kump, John Leone Dean at the College of Earth and Mineral Sciences and professor of geosciences; Kate Meyers, who obtained her mastery of Penn State in 2023; And Emily Stoller, undergraduate research assistant, contributed to the recent study.