Date of Award

2014

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Environmental Sciences

First Advisor

Thomas Boving

Abstract

Nonpoint source (NPS) pollution is one of the major sources of environmental contamination in the United States. Depending on the contaminant and its origin, NPS pollution can be introduced through atmospheric deposition or in the aqueous phase, for example through stormwater runoff. Here, both the atmospheric deposition of 16 EPA priority polycyclic aromatic hydrocarbons (PAHs) was measured at six different sites in Rhode Island as well as their removal, including other contaminants, from stormwater runoff. For the first part of this study seasonal and spatial variation in atmospheric PAH deposition rates were quantified along with investigating the source of the PAHs. The atmospheric deposition of PAHs followed an urban-to-rural gradient with deposition rates significantly higher in urban areas (up to 2261 μg m-2 yr-1 ΣPAH16) compared to rural areas (as low as 73.6 μg m-2 yr-1 ΣPAH16). In fall and winter, PAH deposition was up to 10 times higher compared to summer/spring. In part two of this study a stormwater best management practice (BMP) was evaluated for its contaminant treatment efficiency, with specific attention paid to PAH removal and microbial load reduction. Because many BMPs are not designed to treat bacteria specifically, a novel engineered material, amended red cedar wood chips with different loadings of two antimicrobial compounds: 3-(trihydroxysilyl)propyldimethyloctadecyl ammonium chloride (TPA) and silver nanoparticles (AgNP), was developed and tested in the laboratory to target microbial load reduction and removal of stormwater co-contaminants, including PAH. Laboratory tests showed that E. coli inactivation, at 25°C, can be achieved with log10 removal values (LRV) up to 3.71 ± 0.38 (mean ± standard error) for TPA-red cedar and 2.25 ± 1.00 for AgNP-red cedar, while unmodified red cedar only achieved 0.45 log10. Similarly, PAH removal from the aqueous phase was 68.9 times higher using TPA modified red cedar compared to the conventional shale used in the tree filter BMP. After the screening under laboratory conditions, bioactive TPA amended red cedar wood chips were tested in a pilot-scale field project using a tree filter BMP. The performance of the amended wood chips was compared to a commercially available tree filter BMP that contains a mixed sand/shale filtration matrix. Under pilot test conditions, the two filters performed similarly with regards to bacteria removal. But, the tree filter containing amended red cedar was significantly more effective at removing PAH. As demonstrated in the first part of this study, PAH influxes to stormwater are not limited to local sources, e.g. automobiles, but also have an atmospheric deposition component. Also, because PAH are just one of many contaminant classes present in stormwater runoff, it is therefore important that innovative BMP technologies have multi-contaminant treatment capabilities that can effectively prevent contaminants like PAHs, heavy metals, and/or bacteria from entering the environment. While this study has shown that tree filters can be modified to meet that expectation, more work is necessary to develop, improve and demonstrate a full-scale BMP device.

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