Environmental Science & Engineering Magazine | June 2018

Page 34


Developing new stormwater treatment designs for trapping contaminants of concern By Devrim Kaya, Allen P. Davis and Birthe V. Kjellerup


or more than 50 years, environmental scientists, natural resource managers and regulatory agencies have recognized urban stormwater runoff as an important source of contaminants of concern in waterways. Polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and heavy metals bind to stormwater particulate matter and settle into aquatic sediments, where they persist for decades, impact the health and behaviour of aquatic life, and accumulate up the food chain. In one three-year project, researchers from the University of Maryland will design a modular stormwater treatment system ready for field testing, based on data collected at three test sites. The final design could be applicable at industry sites and in communities anywhere. In the first phase of the project, the team will develop various inexpensive geomedia capable of capturing the contaminants. PCBs and PAHs adsorb strongly to particulate matter and media with high organic content, and dissolved copper forms pH-dependent surface

complexes with organic and inorganic material. In fact, preliminary results from ongoing studies of PCBs in deposited stormwater sediment at the University of Maryland suggest that a large fraction of contaminants of concern could be removed by simply trapping particulate matter. Possible sources for the geomedia, based on the findings of previous studies, include locally-sourced “standard” bioretention media and amendments such as yard waste, wood chips, activated carbon, biochar, aluminum, and/ or iron oxide. The team will select media based on its high sorption capacity, rate of uptake, leaching potential, and ability to promote biodegradation of PCBs and PAHs and/or to immobilize copper. The team will then develop a stormwater best management practice (BMP) that layers these geomedia in a “treatment train.” This approach will allow site managers to leverage multiple types of chemical interactions, including partitioning, filtration and adsorption, to capture a larger concentration of contaminants, without

The idea of clean water is easy to grasp.

causing clogs that would require more frequent maintenance. With help from a passive sampling strategy that monitors reduction levels, site managers will be able to mix and match the layers to create the optimal system for a location’s contaminants and climate and to know when to replace modules as their effectiveness begins to wane. The project will address several key research questions. Firstly, what are the fundamental processes that determine the concentrations and mass loadings of PCBs, PAHs and copper, distributed among different size fractions and organic content of the stormwater particulate matter? How will PCB congeners distribute among different stormwater particulate matter fractions? How can this be exploited for designing treatment systems? The project will look at which types of geomedia will be able to most effectively remove PCBs, PAHs and copper from the stormwater to comply with varying discharge criteria, and at how these types of geomedia influence the Stormwater Quality Services include: Ministry of the Environment Compliance Inspections Oil/Grit Separator Unit Tracking Stormwater Flood Response Lab Analysis Stormwater Ponds Small Spills Removal Jellyfish® Filter Consulting

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Simply put . . . all life depends on it. 34  |  June 2018

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