A recent study by researchers at Penn State University has provided new insights into the migration of nutrients from wastewater disposal sites in the Florida Keys. The study, published in the journal ACS ES&T Water, tracked the movement of nutrients from shallow disposal wells in the region, with the aim of understanding the impact of wastewater on nearshore waters. The data collected over two years highlighted potential contamination of groundwater and coastal waters, prompting a reevaluation of current wastewater treatment practices.
Many treatment facilities in the Florida Keys use shallow injection wells to dispose of treated wastewater, assuming that nutrients like inorganic phosphate would adsorb to porous limestone bedrock as the plume travels underground. However, initial findings from the study suggest that this method may not be as effective as previously thought. This led an environmental group to file a lawsuit against the city of Marathon for alleged pollution from shallow wells, eventually resulting in the city transitioning away from their use.
Monitoring wells were installed around a wastewater treatment facility in Marathon, and data on nutrients, dissolved ions, and human-produced compounds were collected over a two-year period. While the shallow injection process removed over 90% of soluble reactive phosphorus (SRP), traces of SRP and other contaminants were still detected in nearshore waters. This raised concerns about the incomplete removal of nutrients from wastewater, highlighting the need for further evaluation of disposal methods.
The research team, led by Assistant Professor Miquela Ingalls, emphasized the importance of reevaluating wastewater disposal mechanisms at facilities with large discharge capacities. Analytical and quantitative approaches used in the study can help determine whether wastewater injection should be considered equivalent to a point-source contaminant discharge, based on factors such as the effectiveness of nutrient removal and potential environmental impacts.
The study also explored the efficiency of phosphate adsorption onto carbonate bedrock in the Florida Keys and traced the movement of wastewater plumes using fluorescent dye. The high salinity of groundwater in the region, combined with the buoyancy of injected wastewater, raised concerns about the direct transport of contaminants to nearshore waters. This highlighted the complex interplay between geology, hydrology, and environmental impact in the Florida Keys.
Ongoing research by the team is now focusing on the levels of nitrogen in wastewater, as both phosphorus and nitrogen can contribute to eutrophication and harmful algal blooms in marine ecosystems. By studying the chemical processes and microbial communities involved in nutrient cycling, the researchers aim to further understand the potential impacts of wastewater on water quality and ecosystem health. The study was supported by funding from the U.S. Environmental Protection Agency.
Overall, the findings from this study shed light on the complex pathways through which nutrients from wastewater can reach coastal waters, posing risks to marine ecosystems. By reevaluating current wastewater treatment and disposal practices, researchers hope to minimize the impact of nutrient pollution on sensitive marine environments. Continued monitoring and analysis will be essential to address these challenges and ensure the long-term sustainability of water resources in the Florida Keys and beyond.
