Project Team

Student(s)

Natalie Neptune
Civil & Environmental Engineering
Penn State Harrisburg

Mentor(s)

Project Video

Project Abstract

In Pennsylvania, climate change is anticipated to increase the number of dry days between precipitation. These dry days will increase the time stormwater sits in stormwater retention systems. As a result, processes such as resuspension, sedimentation, chemical reactions, and coagulation are occurring and potentially cycling, which affect the settleability, tolerability, and bioavailability of the discharged water. This research seeks to improve the understanding of metal complexes with ligands (such as nitrate and phosphate in stormwater and chlorides found in snowmelt runoff) that are common in stormwater, especially during times of extended detention. Complexation is anticipated to happen more due to climate change as the time increases that this water sits in detention systems. The creation of complexes negatively affects the treatment systems, because the systems were designed to remove the ionic forms of the metals. Metals complexes in stormwater have not been studied, whether at equilibrium or the kinetics of the system until equilibrium has been reached. Changes in certain factors, such as pH, dissolved organic matter (DOM), temperature, and chloride and their impacts on metal complexes have not been well studied in detention systems. In this research project, the equilibrium model Visual Minteq calculated the different complex concentrations using the data from the National Stormwater Quality Database for the ligand and metal quantities. A review of the data showed that most of the ions had a charge of –1 or +1, not the +2 charge of the uncomplexed metal ion. Using a factorial analysis of these 4 factors, Minitab was used to find which factors were significant in predicting the percentage of complexes in each of the two charge groups. Chloride and DOM were the two factors that affected the percentage of copper and zinc complexes in each of the two charge categories. Since chloride is a salt, this indicates the high possibility that road salt contributes heavily to the increase of metal complexes forming, which then could affect its treatability. DOM from the decomposition of organic materials such as plants and living organisms also has a large impact on metal complexation. This impact would be year-round, as opposed to the winter impacts of chloride. These results address a part of the gap in research to understand what affects the ability of treatment systems to clean up the pollutants from stormwater. This also will help increase understanding of the interactions of metals and ligands, especially when quiescent time is available for these systems to go to chemical equilibrium

Project Poster

https://sites.psu.edu/climatedrawdown2020/files/formidable/6/MC-REU.pdf